# Cutting out on 2-3 shift



## BobG (Dec 20, 2006)

I posted a question very similar to this a while back (last year, or so) ... here's the situation ... 

On hard acceleration (WOT), the goat is fine through the 1-2 shift, but before the 2-3 shift, it seems to cut out. 1-2 shift happens at about 4700-4800 RPM. 2-3 shift happens at about 4900-5000 RPM.

here's the technical details for those who need them to come up with a solution:

Motor: Pontiac 400 CI (6.6L), 5000 RPM redline, 10.5:1 CR, TH-400 Transmission , 3.90 rear end
Fuel system: Holley 650 CFM spreadbore, Vacuum secondaries, Secondaries jetted with #64 jets.
Ignition: points & condenser ... Dwell set at 25 degrees, Initial timing set at 16 degrees BTDC, total timing advance is 36 degrees at about 2800 RPM.

Earlier this week, I had a problem with sputtering and backfiring during WOT runs above about 4000 RPM. upon investigation, I found that the seal around the Secondary actuator diaphragm was leaking, and the secondaries were not picking up. I reseated the diaphragm and cap, and tightened all 4 screws, and had much better performance, but still with cutting out above about 4800 RPM in second

I re-jetted the secondaries with #66's and took it out ... It seems to pull harder, especially through and after the 1-2 shift, (I'm breaking the Drag radials loose on the shift ) but I'm still getting some cutting out up around 4900 RPM.

my questions are:

does this seem like a fuel delivery issue (leaning out) or is it a timing issue (not enough/too much advance, not enough/too much dwell, or point gap too close/too far), or some other issue?

Should I go up another size or two on the secondaries, or go up a couple of sizes on the primaries?

I don't have, nor do I have access to a wideband A/F meter, and even if I did, how would I read the value when the secondaries kick in?

For the record, I don't know what size the primaries are. As I am typing this, I am thinking that might be something good to know. If you need any more info to come up with an opinion, please ask...


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## Too Many Projects (Nov 15, 2008)

It sounds like the points may be floating or the coil is too weak to recover at that rpm. Make sure the points are the heavy duty ones with a screw to retain the wire and condenser. Also use a small amount of cam lube on them to prevent binding on the shaft, which can cause bounce too.


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## geeteeohguy (Feb 2, 2008)

In my opinion, your carburetor is too small. The stock carb for your engine is rated at 750CFM. To me, in light of your jetting changes/effects, I would go there first. I do agree with TMP on the ignition check, but I just feel you're undercarbureted/running too lean. Keep us posted!


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## BobG (Dec 20, 2006)

geeteeohguy said:


> In my opinion, your carburetor is too small. The stock carb for your engine is rated at 750CFM. To me, in light of your jetting changes/effects, I would go there first. I do agree with TMP on the ignition check, but I just feel you're undercarbureted/running too lean. Keep us posted!


I do agree that I am undercarbureted ... the Holley spreadbore, from what I have been able to determine, 1)robs some hp from the motor 2)has very few of the 'good' holley features and 3)has none of the good Q-jet features. That being said, my rebuilt Q-jet is still way out there on the project / expense list, so I need to make do with what I have.

Thanks for the suggestions ... I'll check out the points, and the primary jets. Lars always recommended an 8 spread between primary and secondary jetting. That means that my primaries should be 58, which I doubt they are.

I also have a set of #67's that I can toss into the secondaries, but I think I should check out the primaries and the points first ... 

I'll keep you guys posted, and thanks for the responses.


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## Too Many Projects (Nov 15, 2008)

I missed the "spreadbore" carb part.....put 62's in the front and 70's in the back.


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## BobG (Dec 20, 2006)

Too Many Projects said:


> I missed the "spreadbore" carb part.....put 62's in the front and 70's in the back.


Really? that big? I'll try it, as I'm willing to try anything at this point. 

given that I will get the 62's and 70's, how soon after that, mileage-wise, should I inspect my plugs to see how I'm running?


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## Too Many Projects (Nov 15, 2008)

BobG said:


> Really? that big? I'll try it, as I'm willing to try anything at this point.
> 
> given that I will get the 62's and 70's, how soon after that, mileage-wise, should I inspect my plugs to see how I'm running?


Look at them now for a base color. They are most likely pure white. As Jeff said, the carb is too small to begin with and jetting it up may compensate a little. If the plugs get too dark after the change, start bringing them down.


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## BobG (Dec 20, 2006)

OK, I re-jetted to 62/70. I still cut out at about 4900 RPM. So I started looking at the ignition settings .... according to Lars, most carburetor problems are actually ignition problems. I decided that my mechanical advance was a bit sluggish. so I oiled all pivot points and bearings, worked the oil in, and wiped off all excess oil...

now ... it seems like I have less power / torque .... I did not check the dwell after I oiled things ... but ... does this pretty much confirm that my problem is an ignition problem, or is it inconclusive


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## geeteeohguy (Feb 2, 2008)

We know that the carb is too small for the engine. When repairing cars, eliminate the known problem(s) first.


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## BobG (Dec 20, 2006)

geeteeohguy said:


> We know that the carb is too small for the engine. When repairing cars, eliminate the known problem(s) first.


Okay ... I'm trying to get that scheduled for the weekend after next ... I might be able to trade this holley for a Qjet, and get an old chevelle SS guy to assist me in tuning the old goat ...


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## Eric Animal (Oct 28, 2007)

I had a similar problem a few years back....carb was too small, and not enough fuel delivery (pressure)......basically the engine was starving out at high RPMs under heavy load. Eric


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## auburnconsulting (Nov 3, 2008)

on our 65 the points were bouncing at higher rpms doing the same thing. put new distributor in . our 67 had a weak feul pump spring and would not supply enough feul at high rpm. new pump fixed that. the feul pump problem felt differnt , like it would nose over, fall flat on its face. like a bog. the points felt like a miss. both were similar but felt very different. had a blazer do the same, we had to add 2 ground straps frame to body , engine to frame. stopped missing at high rpm above 5000-6500


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## 1AMike (May 11, 2009)

This one is from experience so as stupid as it sounds it is an easy one to test.

Are you running with the air cleaner on? If the answer is "I've tried it without the air cleaner," then read no further,

The air cleaner can cause a fuel problem the other way.

If your car does not detonate (ping) before it cuts out this may indicate a too rich situation and too rich can be easily caused by an air cleaner.

My experience in detail. My '66 had the original style pancake air filter on it. On the street it cut out at 4000. First I replaced the fuel pump: no change. Then I looked at the pancake filter with it's sets of 3 slots and said, "that thing has to be a problem. I put a '67 style HO air cleaner on it and that seemed to cure it on the street. I went to the track and it cut out at 5000 rpm. Took off the air cleaner removed the hood insulation (just so the engine would not suck it in) and VIOLA! no more cut out. I changed NOTHING else. 

I kicked myself because I had thought there was some bigger problem for 4 years before I swapped and then ran without the air cleaner.


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## 70gto (Mar 19, 2008)

I run the spread bore holley stock out of the box for 8 years now, 650. I was under the impression that Holley carbs are slightly bigger than they state compared to a Quadrajet. Been running this carb set up since 1983. But this last one was new . I dont race it , it has a ram air 4 cam, #12 heads with rollers, 1.5, stainless valves, trw pistons, 3.55 rear, auto trans, 2100 stall, headers, stock manifold. I have recurved points distributor in a box waiting to put in... So am i undercarbed? I used the formula a few years back and I thought it comes in around 630 to 670 cfm. for a 70 400 engine.


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## geeteeohguy (Feb 2, 2008)

Hard to say. If it runs well, probably not. You could bolt on a 750 or a 780 Holley and see if it runs harder with your combo. You're running #12 heads........Do you have dished pistons? I could never get my #12's to run without pinging in my '67 400....


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## 70gto (Mar 19, 2008)

They are trw forged replacement pistons, not dished. I use 104 octane boost, the heads are not shaved at all, I had a set of#16 milled and could not control ping. We can get 93 octane in Delaware. that might help. It might pull harder with a bigger carb....then I would just start breaking stuff lol.


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