# New post on carburator hesitation



## Baaad65 (Aug 29, 2019)

Ok fire away PJ


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## BearGFR (Aug 25, 2008)

Is your ride having this problem? I know a little.....

Bear


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## PontiacJim (Dec 29, 2012)

OK, said this before, not a Holley guy, but........

You said "double pumper." Ok, I get that. 

Is it mechanical secondaries or vacuum?

What intake again? Single plane or dual plane?

Just trying to get a handle on some basics which could cause that stumble.


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## Baaad65 (Aug 29, 2019)

BearGFR said:


> Is your ride having this problem? I know a little.....
> 
> Bear


You can see the problem on YouTube under "461 carb hesitation " and yes it does it under load.


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## Baaad65 (Aug 29, 2019)

PontiacJim said:


> OK, said this before, not a Holley guy, but........
> 
> You said "double pumper." Ok, I get that.
> 
> ...


It's a Quick fuel QFT 850 mechanical secondarys, Edelbrock Performer Rpm w/ a 1/2" phelonic spacer. I posted the build sheet in the "another timing question " thread and all that's different is it now has #84 jets in the secondary vs. #82 and #75 jets in the front vs. #74 because that's what I had at the time.


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## PontiacJim (Dec 29, 2012)

Baaad65 said:


> It's a Quick fuel QFT 850 mechanical secondarys, Edelbrock Performer Rpm w/ a 1/2" phelonic spacer. I posted the build sheet in the "another timing question " thread and all that's different is it now has #84 jets in the secondary vs. #82 and #75 jets in the front vs. #74 because that's what I had at the time.


Yep,I recall you posted your info.

My opinion on it.

Not a fan of mechanical secondaries versus vacuum secondaries. Vacuum is more forgiving and better transition for a street engine.

Is the phenolic spacer a 4-hole spacer or open spacer?

You want to keep air velocity up, and the 4-hole spacer is what I would use. The open spacer could be causing problems. The manifold is a dual plane and with an open spacer, you are cancelling some of the function of the dual plane intake. This could affect air/fuel velocity and fuel distribution. 

I don't think the larger jets will have much bearing on the hesitation - just lean or richen up the fuel mixture in general - which you can see on the plugs.

Have you adjusted up the accelerator pump? The pump arm must move as soon as the accelerator pump cam moves.

Here is what I find in one of my Hot Rod books:

First, with mechanical secondaries, make sure they are fully open. You may have to bend the small linkage rod to achieve full opening. Once this has been done, then adjust the accelerator pump, then tune the secondary pump squirter and secondary pump cam.

Place plastic cam in its full stroke position.
Adjust the pump over ride spring - 30cc pump is 1/2"-5/8" visible end threads, 50cc pump is 1/8" visible end threads.
Change squirter size - decrease if too rich, increase if too lean.
Change cam position if if decreasing squirter size has no effect.
Change the cam out if the squirter size or cam position doesn't work.

Give the above a try, if you have not already. Several You Tube videos will also help with the above.

Then post your results.


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## armyadarkness (Dec 7, 2020)

I'm going to be the guy who tells you to get an Edelbrock carb. Not because you will, not because you should, just because someone has to give horribly, irrelevant advice in here, otherwise we cant qualify as the internet.

Hat's off to you Holley guys. Man those things are so much more difficult to tune than a Carter/ Edelbrock. Hard to believe they became so popular.

The good news is, carbs are almost as expensive as fuel injection, now.


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## Lemans guy (Oct 14, 2014)

A carb is an organized leak!…..up the squirter, check both “Umbrella valves” for the accelerator pumps,Matheus deform quickly and effect the squirt. I agree with PJ on the 4 hole spacer, that make a big difference as well.

shoot Gumout down all 8 air bleeds, just a quick shot….The rich of air when secondaries open is causing the lean hesitation, the 4 hole may help increase velocity as PJ said and therefore Venturi vacumn to suck the fuel from the secondary jets.

Either way a tad more fuel needed it appears. An AFR gauge would be super to tell if your hesitation is caused by a lean or rich condition. But most likely it is too lean


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## armyadarkness (Dec 7, 2020)

Lemans guy said:


> A carb is an organized leak!


lol


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## armyadarkness (Dec 7, 2020)

My issue is weird, when I stab the throttle at cruise, my AFR gauge instantly goes to 9, then milliseconds later normalizes and runs at my set jetting. On an Edelbrock carb, that likely means that my secondary air valve spring is too tight, but Im sure that's not going to apply to a Holley.


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## Lemans guy (Oct 14, 2014)

On his Quick Fuel Tech carb, which is just like a Holley but way more adjustable on each circuit, the stab of the pedal requires an adequate squirt from the Accelerator pump of which he has 2. That covers the transition and rush of air …….


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## Baaad65 (Aug 29, 2019)

armyadarkness said:


> I'm going to be the guy who tells you to get an Edelbrock carb. Not because you will, not because you should, just because someone has to give horribly, irrelevant advice in here, otherwise we cant qualify as the internet.
> 
> Hat's off to you Holley guys. Man those things are so much more difficult to tune than a Carter/ Edelbrock. Hard to believe they became so popular.
> 
> The good news is, carbs are almost as expensive as fuel injection, now.


I know I hear that all over but I have 600.00 into this one and I like my fuel rail setup so I'm going to make it work come hell or high water, other than this wot hesitation it runs like a beast 👍


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## armyadarkness (Dec 7, 2020)

Baaad65 said:


> I know I hear that all over but I have 600.00 into this one and I like my fuel rail setup so I'm going to make it work come hell or high water, other than this wot hesitation it runs like a beast 👍


Aside from their atrocious customer service, Holley has nothing to prove with me... If I had access to a dyno, I'd love to take a Quickfuel or Proform and tune it! I'm really only breaking stones about the Eddy carbs, but they do get an undeserved bad rap. If my car runs, Im happy either way.


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## Baaad65 (Aug 29, 2019)

Lemans guy said:


> A carb is an organized leak!…..up the squirter, check both “Umbrella valves” for the accelerator pumps,Matheus deform quickly and effect the squirt. I agree with PJ on the 4 hole spacer, that make a big difference as well.
> 
> shoot Gumout down all 8 air bleeds, just a quick shot….The rich of air when secondaries open is causing the lean hesitation, the 4 hole may help increase velocity as PJ said and therefore Venturi vacumn to suck the fuel from the secondary jets.
> 
> Either way a tad more fuel needed it appears. An AFR gauge would be super to tell if your hesitation is caused by a lean or rich condition. But most likely it is too lean


Parts are on the way and I picked up a cam kit yesterday so I'm going to try maybe the blue cam first for a bigger initial shot...I know one thing at a time starting with the easiest...the gumout shot first.


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## Baaad65 (Aug 29, 2019)

PontiacJim said:


> Yep,I recall you posted your info.
> 
> My opinion on it.
> 
> ...


So I had a 770 street avenger vac secondary but it just seemed like it should have more power and I didn't think the vacuum secondary played well with a manual transmission. The pump linkage is all good with fuel showing soon as I crack the throttle. I guess my thinking on the spacer was first keep the heat away from the carb which it's doing well and second I was thinking it makes the manifold kind of a hybrid of a single plane and dual plane and giving equal amounts to each cylinder in case one was robbing another idk maybe that's a dumb idea, and when I got the FBO tuning book it said just what you're saying to use a four whole instead so know I screwed that up, guess I'll be changing that out.


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## Baaad65 (Aug 29, 2019)

PontiacJim said:


> Yep,I recall you posted your info.
> 
> My opinion on it.
> 
> ...


Forgot to mention previously I got the idea of the open spacer from reading some stories about people milling down the divider in the Performer rpm for more even distribution, maybe that is a fallacy but mine is only a 1/2".


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## armyadarkness (Dec 7, 2020)

Baaad65 said:


> Parts are on the way and I picked up a cam kit yesterday so I'm going to try maybe the blue cam first for a bigger initial shot...I know one thing at a time starting with the easiest...the gumout shot first.


Thats what Id try


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## armyadarkness (Dec 7, 2020)

Baaad65 said:


> Forgot to mention previously I got the idea of the open spacer from reading some stories about people milling down the divider in the Performer rpm for more even distribution, maybe that is a fallacy but mine is only a 1/2".


Seems to me that opening a dual plane would be a waste. Open planes are already perfected and from what Ive heard, opening a dual plane will screw with the needed vacuum signal for the carb


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## BearGFR (Aug 25, 2008)

Ok, since we're dealing with a "Brand H" carb, and I'm going to assume that you have reasons to want to keep what you have and make it work instead of giving up and swapping it for something else....

Primary and/or secondary jet size has zero, zilch, nada to do with hesitation from an idle, either in neutral or under load. The whole and only purpose of the accelerator pump is to provide a momentary supply of fuel to the engine whenever the throttle plates are opened quickly, so as to "carry it through" that interval of time when you've just dumped a bunch of air into engine _but the jets haven't started passing fuel yet. _ So it doesn't matter how large or small the main jets are. They aren't doing anything during this period of time.

Hesitations like the _very slight one_ in the video in neutral (so slight that if it were me I'd ignore it as long as it didn't happen under load in gear), and the more irritating/problematic ones that happen when you hit the loud pedal in gear and want something serious to happen are caused by one thing and one thing only: incorrect fuel mixture. The engine is not getting the "correct" amount of fuel it needs to "go with" the amount of air it's being fed. It's more common for the problem to be caused by not enough fuel (lean) but it can also be caused by too much fuel (rich) and it can be difficult to tell which it is. This is one problem that an air/fuel meter can't help you solve because it can't react fast enough to register whether the problem was too lean or too rich.

Like most everything else on our cars, more is not always better. Sometimes folks will just assume the problem is "not enough" pump shot to a carb that's already too fat, adding more and more, then get frustrated when the problem gets worse and not better. Tiny and undetected manifold vacuum leaks can also play havoc with your tuning efforts.

Another mistake that can be made is getting tunnel vision and working ONLY with the accelerator pump when it's not the cause. This isn't very likely on a Holley but it sure can be with a QJet. I know because I fought one of those myself on my car for a few months several years ago.

But, we're dealing with a mechanical secondary Holley on this thread so I won't take that detour here.

The first thing you should condition yourself to understand and accept is that your engine's fuel demand is going to be different in gear/under load than it will be sitting in neutral and it may not be possible to completely eliminate the hesitation in both situations. The reason is how quickly the engine can build RPM, which affects the amount of time it takes for it to "suck" hard enough to get air flowing through the carburetor and for that air flow to bring the main jets "online" and feeding fuel. Sitting in neutral with no load, RPM and therefore air flow both build pretty quickly (usually) so the main jets activate pretty fast. In gear and pulling hard, it takes a lot longer for that to happen. If you're following along to this point, you should be able to guess that under loaded conditions it's going to need "more" of a pump shot to carry it through this transition period.

Ok - mechanical secondaries. All this really means is that the secondary opening rate is not in any way related to engine load or air flow through the carb. If you hit the pedal, they're going to open and start dumping air into the engine - period. This is the real reason that mechanical secondary Holley's are also always "double pumpers". You need an accelerator pump circuit to deal with that "air dump" on the secondary side just like you do on the primary side. This also makes them harder to tune because now you've got TWO pump shots you have to get right instead of just one. Harder, but not impossible. Tuning the pump on the secondary side can be more of a challenge because of the how the throttle linkage works. They secondaries don't open at the same time or rate as the primaries. They open slightly later than the primaries, and they also open more quickly so that "both ends" of the carb get to wide open at the same time. So the secondaries then don't start to open (and dump air) until the primaries have already opened "some" - and air flow through the primary side has already (hopefully) begun to ramp up and the primary pump has already delivered at least some of its pump shot. When the secondaries start to open, that process starts over on the secondary side AND it has to be balanced with what's already been happening on the primary side. This makes it harder to get right. Harder, but not impossible.

The BEST thing about Holley carbs is that all the circuits on them are almost infinitely adjustable.

The WORST thing about Holley carbs is that all the circuits on them are almost infinitely adjustable.

This means you have a multitude of opportunities to get things wrong with enough leeway to REALLY screw things up, but a combination of a lot of different things that you have to get right - all at the same time.

Ok - finally - what to do and how to do it.

If you do a web search, and you probably have, you'll find volumes of information about tuning Holley accelerator pumps with all kinds of recommendations and "cookbook" "trick of the month club" posts about WHAT to tweak, but very little information about the associated WHY behind those passionate assertions.

Now you know what you're trying to do: tune both accelerator pumps so that they deliver the RIGHT amount of fuel in terms of fuel volume, delivery timing, and delivery duration to carry your engine through the transition period between throttle opening and the main circuits starting to feed fuel.

You've got these adjustment "knobs" available to you.
Pump linkage/lever adjustment
Pump cam size and shape
Pump "squirter" nozzles
Two different pump capacities in the form of two different pumps (30cc or 50cc)
(plus a related adjustment on mechanical secondary that folks tend to not think about - secondary throttle plate linkage)

First thing, do your best to figure out if your hesitation problem is because of too much or too little fuel. I strongly recommend tuning to get rid of any "under load/in gear/I want all that Pontiac torque NOW" hesitation problem you have and then just "accepting" any "sitting in the Sonic parking lot trying to impress your buddies" hesitation you still have (because you probably won't be able to get rid of both), but that's your choice.

A 'too lean' hesitation is USUALLY indicated by the fact that the engine falls on its behind the very instant you hit the go pedal. A 'too rich' hesitation is USUALLY indicated by the briefest instant where it seems like it wants to go, but then changes its mind. USUALLY, not always --- this is one of the reasons this job can be challenging.

Here's what the knobs do, why you care, and which way to turn them to make a change.

*Pump linkage/lever adjustment*
This controls WHEN the pump shot starts in relation to throttle opening. See that spring on the pump actuator? It's there to provide more than just an adjustment. When it starts to move the pump and shoot fuel, that fuel can only be forced out of the pump chamber as fast as the pump nozzles will allow it to be shot - remember that liquids are essentially not compressible. If that spring wasn't there, then every time you stomped on the pedal you'd rupture the pump diaphragm. That spring is there so that the pump can dump fuel as fast as the nozzles will allow, but no faster. You'll find all kinds of recommendations about using a feeler gauge to set the distance between the plunger and the actuating lever to a specific setting. Within reason, ignore those. GENERALLY (you'll find that word used a lot) you want the pump to start shooting fuel at the very instant those throttle plates move - otherwise it means the engine will be getting air but no pump shot to go with it at first. This means setting the clearance between the plunger and the pump lever at zero. The reason there's a clearance spec for that adjustment is to avoid trying to push the pump diaphragm past its maximum travel limit - which will rupture the diaphragm and potentially start dumping fuel out the bottom of the pump housing and all over your hot engine. Not good. Also realize that changing the idle speed adjustment on either end of the carb (mechanical secondary Holleys have an adjustment for this on the secondary end too) will change the orientation of the pump linkage and thus the clearance between the pump lever and the pump actuating spring plunger. So, if you get everything "perfect" and then change your idle speed setting, you'll have to do this again. Fun.

*Pump Cam*
The cam controls how MUCH *fuel volume* the pump will deliver at a specific throttle opening, determined by the shape and slope of the cam lobe. There are lots of charts out on the internet that show how the various pump cams behave. Just remember that the cam controls delivery volume, not (necessarily) delivery rate.

*Pump Nozzles*
Pump nozzles are the primary control for pump fuel *delivery rate. *The smaller the nozzle, the longer it's going to take for a given volume of fuel to pass through it at a given pressure. Pump nozzle size also therefore influences how long the pump shot will last. The smaller the nozzle, the longer it will take for the shot to be delivered.

*Pump*
Holley makes two different pumps. One that delivers a maximum of 30 cc's of fuel and one that delivers a maximum of 50 cc's of fuel. They each use different actuating linkages and cams. There are only two cams available for the 50 cc pump.

I just talked about what all the components do as if they're all isolated, but they aren't really. Changing one will always affect the other and it's important to know that.

For example, The pump diaphragm can only exert so much pressure without rupturing, and that pressure comes from the combination of the spring tension on the pump actuating plunger and the throttle opening rate. At max pump operating pressure (limited only by plunger spring tension in the case where you just stomped on the pedal) the delivery rate of the shot and its duration is controlled by the pump nozzles - maybe. If you have a really mild pump cam that doesn't move the pump through its full travel, then you won't get the maximum pump volume (30 cc or 50 cc)
Also, you probably don't always stop the pedal. If you slowly roll into it, and/or don't always go to WOT, that affects both the pump delivery rate and volume.
If you don't have the pump linkage set so that it delivers fuel instantly with throttle movement, that affects the timing and also, if it's so loose that it doesn't create full travel of the diaphragm, you don't get "all" of the shot.

Nozzle size, cam, and even the spring tension on the pump plunger are all interrelated too. A "lighter" spring tension (or a "loose" spring adjustment) will lower the amount of pressure exerted on the diaphragm and thus lower the maximum pump pressure, which will slow down delivery even without changing the nozzle size. Remember how springs work. The more they're compressed, the more pressure they exert - which also affects pump pressure and delivery rate.

The point I'm trying to make here is that you should always keep your brain engaged. Don't allow yourself to become so focused on just one aspect of tuning the pump, like changing nozzle sizes for instance, that you forget to consider how those changes affect the other aspects and variables of how the pump works. Everything influences everything else. If you get it all "perfect" and then decide a month later and for completely other reasons to decrease your idle RPM, guess what? You just introduced some clearance into the pump linkage which will then delay the pump shot, and you may find your bog has returned and start pulling out your hair trying to figure out what happened because after all it was perfect just yesterday.

So.. make small changes and change only one thing at a time. To simply things, *completely disconnect the secondary linkage and block them shut so that you know they can't possibly open. *This way you can be certain that whatever results you're getting are coming from the primary side and only the primary side. Yeah, it's going to kill performance a little but you don't care about that yet. If you suspect that you have a "lean" stumble, the easiest thing to try is to go to larger pump nozzles and make sure you've 'zero clearanced' the linkage. See if that makes it better or worse. If it's better initially, as in when you hit it it starts to sound like a 'too rich' problem (it goes at first then stumbles) then maybe the problem really is "too rich" (you went too big on the nozzles) or the pump shot is being used up too soon (not enough volume) - try a more aggressive pump cam, slightly smaller nozzles (but still larger than what you started with). If you still can't "get there" then maybe you need to upgrade to the 50cc pump. It might take multiple tries, many adjustment attempts, and you might have to undo things just to try other things, but with perseverance, determination, and logic you eventually WILL be successful. It's not rocket surgery.

Once you get the primary side working right, it'll be time to reconnect the secondaries and start over - on the secondary pump. 
Apply the same logic and procedures.

It's pretty common for double pumpers to come out of the box with the 50cc pump on the secondary side. If you're really unlucky, you might find that the secondary side is "too rich/too big" no matter what you do, and you'll have to convert the secondary side "back to" a 30 cc pump with all the associated cams, linkages, nozzles, and adjustments.

Just remember it's all about delivering the right volume of fuel at the right time.

Bear


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## armyadarkness (Dec 7, 2020)

That was very informative. I never understood Holley's. Then back in the 90's I started racing and working on sport bikes, and the carbs were so basic that the made sense to me. Idle, cruis, and WOT circuits, each requiring a different tuning procedure.

Turn the clock ahead 20 years and when I bought the Edelbrock carb, I was overjoyed to see that it was the same as the motorcycle carbs. Ease of tuning aside, the one thing I enjoy about the Edelbrocks is that they taught me how a carb works, and gave me confidence in my abilities. Now I would buy a Holley in a minute. The quirks or complexities would no longer scare me off. In fact, if I ever get my engine performing well enough, Id love to do a dual quad setup.


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## Baaad65 (Aug 29, 2019)

Great information! And it has the same hesitation under load I just can't film that myself driving. Also stabbing the throttle up to when I can feel it up against the secondary there's no hesitation so I'm thinking it's all in the secondarys.


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## BearGFR (Aug 25, 2008)

Baaad65 said:


> Great information! And it has the same hesitation under load I just can't film that myself driving. Also stabbing the throttle up to when I can feel it up against the secondary there's no hesitation so I'm thinking it's all in the secondarys.


Very possible - however I'd still recommend going through the whole process of tuning "both ends", just to make sure it's right. Unless you put a 'calibrated block of wood' under the pedal so that you can be sure you hit the primaries hard but never touch the secondaries even a tiny bit, it'll be pretty hard to recreate maximum demand on the primary side.

I spent a very frustrating year - 12 full months - "fighting" with mine when I decided to switch to a Holley platform carb after convincing myself I needed more capacity than my much beloved and well tuned QJet could deliver.

I learned the hard way more about them than I ever really wanted to, and I bought every jet, every pump, every cam, every air bleed, every pump nozzle, every idle feed restrictor, every power valve in the Holley parts book and even bought brass blanks to drill and make my own orifices for the various internal passages in it when the sizes I wanted to try just didn't exist anywhere.

My problem was that for the life of me I just could not get the silly thing to quit being over-the-top-pig-battleship-floating rich at part throttle cruise even though it was "right" at idle, launch, and WOT. In my case, having a good full time air/fuel meter in the car was a life saver. Tuning that carb without it would have been impossible.

I just hope my thoughts about the QJet not being big enough were correct. If I was wrong about that, I never ever want to know. 

Bear


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## O52 (Jan 27, 2019)

Makes me love my QJ all the more


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## armyadarkness (Dec 7, 2020)

O52 said:


> Makes me love my QJ all the more


I love Qjets and Holleys! I actually don't like Carters... However, they work easily and were OEM on both my 67's. 

It was too hard to find a reputably rebuilt Qjet or a trusted core, so after a year, I finally just gave up. They were out there for $850, but that was out of my range.


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## Baaad65 (Aug 29, 2019)

Well hopefully I didn't take bad advice and go to big because all the charts say my motor should have between a 750 and 800 but the carb builder said the 750 has the same bore size as the 850 idk how, I did put 1.65 rockers so equivalent to a slightly bigger cam for more air then it should come down to head flow which Butler said mine should flow 220-240. I don't really think the hesitation is a to big of a carb it's tuning and I'll get it whipped...heck I read where Kaufman was sticking 950 -1000 cfm carbs on motors like mine.


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## PontiacJim (Dec 29, 2012)

Baaad65 said:


> Well hopefully I didn't take bad advice and go to big because all the charts say my motor should have between a 750 and 800 but the carb builder said the 750 has the same bore size as the 850 idk how, I did put 1.65 rockers so equivalent to a slightly bigger cam for more air then it should come down to head flow which Butler said mine should flow 220-240. I don't really think the hesitation is a to big of a carb it's tuning and I'll get it whipped...heck I read where Kaufman was sticking 950 -1000 cfm carbs on motors like mine.


Keep in mind that the 1.65 rockers will pop the valves open much quicker and you could lose some port velocity because it is not being built up in the same way the slower opening of the 1.5 rockers will do.

Just for fun you may want to go back to the 1.5's on the intakes only to see if that makes any difference.

When you add an open plenum spacer, or mill the divider on a dual plane intake, it is like making the carb bigger. The carb is no longer split where the engine pulls from one side or the other, instead the engine pulls from all bores of the carb. In essence, a cheap man's single plane manifold version of a dual plane manifold. So the 850 carb could be too large in this instance and again, losing mixture velocity.

An engine will only use the CFM's it wants and why a vacuum secondary type carb works well IF you go too big. With the mechanical secondaries, this is not an option if you go too big because you are forcing the engine to accept 850CFM's, BAM!, when it may not have the intake flow/velocity to make full use of all those CFM's.

Could all of the above be some of the problem, possibly, and more stuff/adjustments to think about.

Bear did a good job of explaining and singling out the various aspects that can be adjusted or checked. The double pumper, in my opinion, really needs gearing that will wind up the engine quickly. If the gearing causes the engine to pull hard rather than wind up fast, the hesitation could be when the secondaries snap open quickly gulping in air that the engine can't rev up fast enough to keep up. If Kauffman is putting 950-1000 CFM carbs on engines like yours, I am sure it has a high stall converter, 4.88 gears, and spins 7,000-7,500 RPM's. 

So work with the carb as Bear outlined getting the primaries working at peak performance. The tackle the secondaries as I have stated before that I think you will find the hesitation coming from some form of needed adjustment or tweaking - too little fuel or too much. I read that the smaller squirters will squirt less gas longer, and the larger squirters will pump more gas shorter. So this can played around with.

Just remember, keep a note book and anything/change you make write down the results. If the change/adjustment does nothing, don't move to the next change/adjustment. Put whatever it was that you did back to its original setting first, then make the next change/adjustment.


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## Baaad65 (Aug 29, 2019)

PontiacJim said:


> Keep in mind that the 1.65 rockers will pop the valves open much quicker and you could lose some port velocity because it is not being built up in the same way the slower opening of the 1.5 rockers will do.
> 
> Just for fun you may want to go back to the 1.5's on the intakes only to see if that makes any difference.
> 
> ...


Thanks for the education and I'm soaking it up, I do remember that about the 1.65 rockers on the intake but unfortunately I sold them as a set, FBO's tuning book is saying I'll lose low end torque and maybe idle to cruise response but gain high rpm power with an open spacer, so I'm not worried about low end on the motor when I got the motor it made 526 lbs and I hav a 2.99 first gear with a 3.42 rear gear also I had this hesitation before the spacer was installed so will get her tuned up...I hope 👍


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## BearGFR (Aug 25, 2008)

Baaad65 said:


> Thanks for the education and I'm soaking it up, I do remember that about the 1.65 rockers on the intake but unfortunately I sold them as a set, FBO's tuning book is saying I'll lose low end torque and maybe idle to cruise response but gain high rpm power with an open spacer, so I'm not worried about low end on the motor when I got the motor it made 526 lbs and I hav a 2.99 first gear with a 3.42 rear gear also I had this hesitation before the spacer was installed so will get her tuned up...I hope 👍


Don't fret too much about having a carb that's "too big". I watched an Engine Masters episode not too long ago where they pretty much proved that's almost a myth. You have to go "stupid big", like putting an 1100 Dominator on a slant 6 before that actually causes issues. There's a point where going bigger doesn't help performance any, sure, but you have to get really crazy before it actually hurts anything. Otherwise you're just "wasting" capacity that you can never really use. 

Bear


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## Baaad65 (Aug 29, 2019)

Ok all so far sitting in the garage temp at 180° I'm encouraged with the throttle response to wot but will see tomorrow as I don't have time for a test flight today. Sprayed out the idle bleeds but didn't help, so I changed the secondary cam to blue in the #1 hole #1 linkage position, hesitation gone then changed out the #31 secondary nozzle to a #35 and no difference but still no hesitation so fingers crossed...the new videos are loading onto YouTube now under "461 hesitation after adjustments " see what you think. Also I have accelerator pump check valves and a 7.5 PV coming so I'm wondering if I should change those out or leave it alone?


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## Lemans guy (Oct 14, 2014)

If the hesitation is gone just hold steady. Keep the check valve they are thin rubber and you will need to replace them someday. The 7.5 PV you can hold just wait and see how it runs.


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## PontiacJim (Dec 29, 2012)

Baaad65 said:


> Ok all so far sitting in the garage temp at 180° I'm encouraged with the throttle response to wot but will see tomorrow as I don't have time for a test flight today. Sprayed out the idle bleeds but didn't help, so I changed the secondary cam to blue in the #1 hole #1 linkage position, hesitation gone then changed out the #31 secondary nozzle to a #35 and no difference but still no hesitation so fingers crossed...the new videos are loading onto YouTube now under "461 hesitation after adjustments " see what you think. Also I have accelerator pump check valves and a 7.5 PV coming so I'm wondering if I should change those out or leave it alone?



OK, so what did you learn from this exercise??????


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## Baaad65 (Aug 29, 2019)

More gas...and if this holds up I'm fortunate to have found people with more experience and knowledge here.


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## PontiacJim (Dec 29, 2012)

Baaad65 said:


> More gas...and if this holds up I'm fortunate to have found people with more experience and knowledge here.


Exactly.  Generally, if you know your ignition is good, fuel system is working as it should, then a hesitation when popping the carb open, whether the initial stab of the gas or the opening of the secondaries, typically means the engine is getting more air than gas - so the air/fuel mixture is off and needs to be adjusted.

Typically, a bigger/longer squirt of gas is needed to compensate for when the throttle blades initially open up and the engine vacuum goes to near zero and can't pull the fuel out of the venturi's within the carb bores. So that squirt of gas from the accelerator pump, that enters the carb through the squirters/fuel nozzels is what adds the gas to that big gulp of air when the throttle blades pop open and creates the required air/fuel mixture that causes the engine to "pick up" rather than hesitate or stumble. Once the engine "picks up" due to this rich squirt of gas, the port velocity is developed by the pistons pulling in the air/fuel mixture and then draws the air/fuel mixture from the venturis inside the carb's primary and/or secondary bores, and off you go. You just have to do some work on adjustments based on the carb type/model and work that hesitation/stumble out of it.

So one of the first things to do is with the engine turned off, fully open the choke flap, look down into the carb with a flashlight, then manually open the carb as you would with your foot going to the floor. You should see a good solid, steady, stream of gas squirting from each side of the gas nozzles and going into the carb primaries, or secondaries if a double pumper type carb. If you don't see this, then begin looking for the reason. Generally, it will be the accelerator pump has worn out or the seal had dried up/shrunk, or deteriorated from the ethanol laced gas if it has never been changed out with an ethanol friendly accelerator pump. Next would be blockage in the enrichment system due to a foreign piece of material, dirt, or corrosion. This may mean carb disassembly and go from there.

Going bigger/smaller on the jetting won't help unless you are getting a "surging" feeling while cruising along - and this can also be a sign of an ignition situation as well. Reading your plugs (which can be difficult at best with the ethanol gas) or using an Air/Fuel Meter as an indicator can also be of great help if you want to at least isolate the carb running rich/lean and then make adjustments to bring the A/F numbers closer to optimum for your build. Just more adjustments that can be looked into if a surging feeling is felt while cruising along.


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## Baaad65 (Aug 29, 2019)

Got it👍 so if I don't get the hesitation with the #35 nozzles I guess I can try putting the #31's back in and see, if it's don't need that big of a shot why use them, it was probably the cam change that helped. And Lemans guy you said you run a 7.5 PV so I have one coming, with 14 inches of vacuum is that a better choice?


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## Lemans guy (Oct 14, 2014)

I run an 8.5 Pv. The reason is I have a vacumn gauge and a dual AFR meter on the dash. To see what PV I wanted I started with the factory 6.5 PV. Now pulling a grade up a long hill your pedal is down, secondaries are not on and this is a sustained pull. Where power is needed. My vac was not low enough to get the extr fuel I wanted at that time, I wanted 12.2 AFR but was still on my main jets at 13.4.

so I tested it under many power conditions and wound up with for me an 8.5 PV, it gives me 122right when I want it. I would say 7.5 may be better than the 5.5 you have.

there should be times when the PV is used without the accel pump and without the secondaries and times when it is used with one or the other and times when all three are in play.


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## Baaad65 (Aug 29, 2019)

Ok but I have a 6.5 PV, went to a show about 30 miles away today and it ran pretty good except for getting stuck in second gear on the way home. It was 90° today so going home after the show I was getting stuck in traffic so my temps were running 200+ and I noticed once or twice a little hesitation off the line after sitting at a light and one time I thought it was surging in 3rd gear, I did bury the pedal a couple times at a stop light and it didn't seem to hesitate and tried to nail it a couple times under load and it seemed pretty good but the wife doesn't like me experimenting with her in the car so I'll have to go out alone. I think the engine temp was affecting things, I have #76 jets I can put in to replace the #75's if I have it apart to replace the PV and inspect the check valve if you think the 7.5 is a good idea.


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## Baaad65 (Aug 29, 2019)

Ok got my 7.5 PV today only to realize I didn't order the high flow one 🤦‍♂️ so idk if that will make a big difference, put it in anyway, changed the accelerator check valve which was in good condition but while I was in there did it. I pulled three plugs and they are a little darker than before maybe from the bigger cam and nozzle? And I put the #31 nozzle back in vs. the #35...will have to test drive it tomorrow and see how it feels. One thing I noticed that might or might not be a concern is when checking the idle vacuum again I can turn the passenger side front screw all the way in with no effect on the idle, I can't do that on the other three so I pulled it out and everything looks fine but I didn't blow any air in the hole and you can't see in there but there was no debris on the screw or gasket. Still sounds good in the garage with no hesitation going to wot from idle.


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## Lemans guy (Oct 14, 2014)

See how it runs after the test drive,…sounds like you beat the hesitation. If it idles fine leave the screws alone


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## Baaad65 (Aug 29, 2019)

Ok, is it worth 12.00 for a high flow PV ?


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## Lemans guy (Oct 14, 2014)

Yes, but remember that the “Power Valve Channel Restrictors” PVCR’s actually meter the fuel flow to the main wells…..


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## Baaad65 (Aug 29, 2019)

Ok, I couldn't see the numbers on those so when I replace the PV I'll take one out and check the size for my records.


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## pontiachristopher (Jun 28, 2020)

BearGFR said:


> Ok, since we're dealing with a "Brand H" carb, and I'm going to assume that you have reasons to want to keep what you have and make it work instead of giving up and swapping it for something else....
> 
> Primary and/or secondary jet size has zero, zilch, nada to do with hesitation from an idle, either in neutral or under load. The whole and only purpose of the accelerator pump is to provide a momentary supply of fuel to the engine whenever the throttle plates are opened quickly, so as to "carry it through" that interval of time when you've just dumped a bunch of air into engine _but the jets haven't started passing fuel yet. _ So it doesn't matter how large or small the main jets are. They aren't doing anything during this period of time.
> 
> ...


hey, was wondering if you could send me on that detour. the accelerator pump on the qjet, i was up on the flashlight thing and didnt notice any pre ignition fuel. it;ll start on its own, 3 cranking tries while pumping the pedal between. some hesitation at start off, its a 4 speed. but if i spray it with the starting fluid, it doesnt even have to crank,just turn the key. the carb, and motor are from a 68 bonneville 400, said 340 hp, 10.5:1. think they said 2 carbs, unsure of cfms? thank you


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## Baaad65 (Aug 29, 2019)

So got the car out after work to test my carb adjustments (blue cam, 7.5 high flow PV) and it ran good, didn't feel any hesitation even when I got back in the driveway stabbing it a couple times but it was cooler today than Sunday, mid '60's. I did smell the clutch a little so maybe it was my take off method but never smelled it before so hopefully it's not slipping. I checked my mechanical advance before I went out and with one blue spring and one light silver it was getting to 34° a little early like 2200-2300 rpms so I swapped out the silver one for another blue and it's getting there around 2500-2800 so that seems better. Also for fun I put the #35 nozzles back in to see if I notice any difference. I guess I won't feel the different PV unless surging is a sign and it did that once on Sunday but it was 90° out and I was running 200° so will see how it feels this weekend. Guess I'll need that AFR gauge to really see where I'm at but for now I'll read the plugs.


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