# Gto trouble



## irelandGTO (Oct 24, 2015)

Hi, hope you guys can help me cos I'm tearing my hair out here, just got a 71 goat not even driven her yet. So she had a blown head gasket which I replaced and had the heads skimmed and valves ground, she has dual Edelbrock 1404 on a 65 intake manifold and a 270h comp cams camshaft 48 heads and ram air exhaust manifold that's the good stuff she runs rough at idle no more than 12" vac and rich as hell anybody got any ideas. I believe it always ran like this but it can't be right?


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## Rukee (Feb 8, 2007)

Is the choke opening all the way? Is there any fuel running down the inside of the carb when idling? Extra dirty air filter? Air mixture screws adjusted proper?


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## irelandGTO (Oct 24, 2015)

Carbs are fine just put a rebuild kit in both, no choke on either carbs.


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## PontiacJim (Dec 29, 2012)

irelandGTO said:


> Carbs are fine just put a rebuild kit in both, no choke on either carbs.


Who rebuilt the carbs?

Have you checked the Edelbrock website? It is my understanding that the performance series carbs are set to be rich assuming a healthy cam will be used. Edelbrock has a "Carb Owners Manual" that will help you calibrate the carb. They off a calibration kit that has all the items you need to do this. Here is the PDF for the Owners Manual http://www.edelbrock.com/automotive/misc/tech-center/install/1000/1404_manual.pdf

Have you tried to adjust your carb using the engines vacuum? A vacuum gauge can tell a lot. Neat YouTube Video to watch here: 




Next question, why did the head gasket blow? Is it possible that it blew out due to detonation? 

What is your compression ratio? 

Have you checked your timing? Nice article here: Distributor advance


These are just a few of the things you might check. It could be one of these, or it could be something else. Very hard to diagnose your problem over the internet, but we can give you ideas to look into. It basically boils down to a process of elimination. :thumbsup:


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## irelandGTO (Oct 24, 2015)

Thanks for the reply Jim. I did the carbs X2 myself the head gasket had a rusted through squash ring on number 6 cylinder it was a felpro gasket. It is my belief that it has been like this for a long time but I can't contact the US owner (Thomas Gormley, Ca.) to confirm. Engine was rebuilt in 2000 don't know who did it. Don't know compression ratio, cylinder compression is 170 psi all within 10%. I was thinking it might be they put the timing chain on a tooth out. The only other thing it does is the lifters are always tappety for a good 4-5 minutes on start up if left for a few hours.


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## TonysGoat (May 16, 2015)

PontiacJim - Thanks for sharing the video, very informative. I just ordered a vacuum gauge and a flexible shaft driver so I can make some tweaks.


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## PontiacJim (Dec 29, 2012)

irelandGTO said:


> Thanks for the reply Jim. I did the carbs X2 myself the head gasket had a rusted through squash ring on number 6 cylinder it was a felpro gasket. It is my belief that it has been like this for a long time but I can't contact the US owner (Thomas Gormley, Ca.) to confirm. Engine was rebuilt in 2000 don't know who did it. Don't know compression ratio, cylinder compression is 170 psi all within 10%. I was thinking it might be they put the timing chain on a tooth out. The only other thing it does is the lifters are always tappety for a good 4-5 minutes on start up if left for a few hours.


OK, got it. It is hard to diagnose any engine when you don't know what parts/brand were used or who assembled it. 

The 12" of vacuum may be about right with the cam you are using. A rough idle may also be part of the camshaft profile - Comp Cams states the cam has a "Fair Idle", so it is going to be a little rough. A performance cam also runs a little rich. So your engine may be running as it should. The Comp Cam is ground on a 110 LSA whereas a factory cam is typically wider at 114-116 which will give you more vacuum, smoother idle, better economy, and a broader power curve. 

The lifter tick could be a number of things, some of which is normal. You may have fast bleed lifters which can bleed down after they set and pump up after your engine starts. It could also be anything from bad lifters to an adjustment needed. Did it do this before pulling the heads? Assume you have good oil pressure? Do you have an oil pressure gauge you can watch when you have the ticking? Also check for an exhaust leak which can sometimes sound like a lifter tick until things get hot and expand.


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## irelandGTO (Oct 24, 2015)

Thanks for your continued help and patience, I didn't run the engine before I pulled the heads and haven't asked the previous owner about the lifters which is why I want to contact the original US owner. Oil pressure is good 50 psi measured from a gauge not the sender unit and fascia panel but it stays at 50 from idle to 2000 rpm.I took her for a run yesterday and she goes like shit of a shovel but very bad manners, not good in traffic at all hard to start when hot very jerky in 1at and hesitant when you floor it. I will pull the timing cover and check the timing marks so I can rule it out as a possible cause but after that I'm out of ideas. Thanks again for the replies.


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## PontiacJim (Dec 29, 2012)

irelandGTO said:


> Thanks for your continued help and patience, I didn't run the engine before I pulled the heads and haven't asked the previous owner about the lifters which is why I want to contact the original US owner. Oil pressure is good 50 psi measured from a gauge not the sender unit and fascia panel but it stays at 50 from idle to 2000 rpm.I took her for a run yesterday and she goes like shit of a shovel but very bad manners, not good in traffic at all hard to start when hot very jerky in 1at and hesitant when you floor it. I will pull the timing cover and check the timing marks so I can rule it out as a possible cause but after that I'm out of ideas. Thanks again for the replies.


Here is my OPINION, I'm no expert, but sounds like it could be the cam that was chosen for the car. When the heads were off, did you notice if the tops of the pistons were either dished or just had the "eyebrows" for the valve reliefs?

If you have the factory style piston tops which have the 4 eyebrows for valve reliefs, plus the 1969 #48 heads with 72cc chambers, your compression on the 400 is up around 10.5 to 1. The car will need a premium gas or race gas with lots of octane. The Comp Cam with the 110 LSA would not be my choice for an engine with 10.5 compression if I were running it on the street. These cams do produce a lot of explosive power in the mid-range, but power will peak quickly and fall off - so the cam really needs a target RPM that it operates at and then a matching torque converter (if automatic), trans gearing & rear axle gearing. The car may hesitate when you stomp it because intake velocity has not been built up at the lower RPM's - this is why you run a 3.73, 3.90, or 4.11 gear in the rear axle or a higher stall converter (if automatic) - this also makes it more streetable and seemingly less jerky on the street. You my be able to compensate for some of the hesitation by adjusting your carb to give you a longer shot of gas from the accelerator pump.

Hard starting when hot can be due to incorrect distributor timing or a gas leak within the carb that seeps down into the intake to create a "rich" start problem. You can drop the distributor timing back a few degrees to see if this helps the hot start problem. Keep in mind that if you have the original factory harmonic balancer that the outer ring can slip on the inner rubber ring and give you a false distributor timing as the balancer timing marks will move if the ring slips.

I can't tell you what to do, but I would call or email Comp Cams and give them your engine build specs and the 270H cam your engine came with and the problems you are experiencing. They may recommend a different cam profile other than the one you have. The cam timing could be off and Comp Cams may even recommend advancing or retarding the cam you have, so I would call them first for their recommendations before you go into the timing cover.


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## irelandGTO (Oct 24, 2015)

It has the factory type pistons forged 0.030 over, I put a new balancer on recently because the old one snapped it's shaft. It has the ram air heads and exhaust manifold 4 speed muncie and 12 bolt posi don't know what the gearing is.
I'll send an email to compcams tonight it sounds like the right thing to do.
It also has a full msd system which I am not familiar with, digital 6a box, msd billet distributor and msd coil no vacuum on the distributor.
Could be the dual quads causing the bad idle/ rich condition, I've heard it said they look better than they perform. Thanks again for the advice.


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## PontiacJim (Dec 29, 2012)

irelandGTO said:


> It has the factory type pistons forged 0.030 over, I put a new balancer on recently because the old one snapped it's shaft. It has the ram air heads and exhaust manifold 4 speed muncie and 12 bolt posi don't know what the gearing is.
> I'll send an email to compcams tonight it sounds like the right thing to do.
> It also has a full msd system which I am not familiar with, digital 6a box, msd billet distributor and msd coil no vacuum on the distributor.
> Could be the dual quads causing the bad idle/ rich condition, I've heard it said they look better than they perform. Thanks again for the advice.


OK, sounds like your good on the trans & rear end. 

The MSD parts are good, have run the 6A on a car in the past and purchased the 6AL (built in rev limiter - which I suggest you add-on if you don't already have an engine rev-limiter). You can adjust the advance curve in the distributor which can make a big difference on how the engine runs. Watch this excellent MSD video on timing your engine and adjusting the distributor curve. Click on this link: https://www.msdperformance.com/support/set_your_timing/ 

The carbs are 500CFM and should work fine as they have the vacuum secondaries. I ran a pair of 750CFM's that were originally for the Ford 460 CI engines (never re-jetted or modified, just rebuilt them and ran as is) on a warmed over 409 and they definitely ran rich cruising around town, but once I got past 2,500 RPM's, they came on strong and never stopped pulling. I turned in the idle screws on the second carb to close them off (I think this worked, but I can't be 100% sure). I used progressive linkage and that got me about 8 miles per gallon and once had them hooked together just to try it, and I watched my gas gauge needle sink to "E" right before my very eyes - went back to progressive linkage. 

Again, it is possible that you need to adjust the carb. With 12" of vacuum, there are enrichment springs - READ Page 5 & 6 of the Edelbrock carb manual link I sent you. With a low vacuum reading as you have, you probably want to change the step-up spring rate as a stock type spring for higher vacuum will not close off the step-up piston and your carb will be running in a rich fuel condition - and I would do this for both carbs. You will need a lighter spring to match your engine's vacuum of 12" at idle. 

I would still contact Comp Cams and inquire about your cam, then you will know for sure, they may have some recommendations for you.

Don't make too many changes all at once. Do one change at a time and see how that change effects your performance. Some fine tuning of an engine is always trial and error. :thumbsup:


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## irelandGTO (Oct 24, 2015)

Thanks again Jim, I'm still waiting to hear from comp cams I sent them an email on Sunday. I will let you know what happens.


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## PontiacJim (Dec 29, 2012)

irelandGTO said:


> Thanks again Jim, I'm still waiting to hear from comp cams I sent them an email on Sunday. I will let you know what happens.


OK, good. I am curious to see what they may say. :thumbsup:


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## irelandGTO (Oct 24, 2015)

Still no word from compcams, so I took the timing cover off and the marks are spot on, someone said the symptoms are similar to valve timing being retarded and I should advance it while the cover is off, what do you think. I know it's not running right even if the vacuum is all I can get something else is wrong for it to miss and surge.


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## PontiacJim (Dec 29, 2012)

irelandGTO said:


> Still no word from compcams, so I took the timing cover off and the marks are spot on, someone said the symptoms are similar to valve timing being retarded and I should advance it while the cover is off, what do you think. I know it's not running right even if the vacuum is all I can get something else is wrong for it to miss and surge.


Advancing or retarding the cam changes the valve to piston clearance. You don't want a valve to hit a piston. You really need to know what the valve to piston clearance is. 

Keep in mind that many cam manufacturers build in cam advance and CompCams is one of them depending on the cam selection, so you might want to check with them. It may take a couple days for a reply. If you don't get a reply, then email them again.

On the CompCam site they tell you how to adjust the valves. If the lifters have too much pre-load, vacuum can be down and the engine can idle rough. Check *Setting Hydraulic Lifter Pre-load 
* and adjusting rocker arms is also covered. Everything you need to know is here: http://www.compcams.com/technical/instructions/files/145.pdf

It could still be a carb/fuel system problem, ignition problem, or something else. Make sure your coil is getting 12 volts to it. When people change over from a points type distributor to an electronic distributor, the electronic distrib. needs 12 volts whereas the points distrib. get about 8 volts and uses a resistor wire to do this. I don't know if your car had points, but I would also make sure I had 12 volts to the coil or this can make it run poorly. Read the MSD installation notes here: http://www.g3ignition.com/images/MSD 6 Series Installation Instructions.pdf


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## BearGFR (Aug 25, 2008)

I'm with Jim. Sounds like the rough idle may be normal for the cam. The other symptoms could be related as well, but with proper fuel (sounds like you've got pretty high compression for a pump gas engine, perhaps too high) - it shouldn't be exhibiting the hesitation and other drivability issues you're describing. I'd start with making sure the timing is correct - and by this I don't mean set it to the factory 6 degree BDTC spec, I mean setting the total mechanical timing at about 2500-3000 rpm. (I've posted on here several times how to do that, should turn up with a search). However, with that much compression the engine may not like what would otherwise be the optimum setting, so, after you get that done - take it out for a leisurely drive, find a nice steep hill and while going up it in high gear around 1500 rpm or so, gradually roll into the throttle. You don't want it to downshift (if an automatic), but you do want to get some significant pull/load on the engine while it's at relatively low rpm. Listen intently for any hint of knock/rattle. If you hear it - that's bad. It's detonation and will eventually destroy the motor. (You can also inspect your spark plugs with a magnifying glass, checking for any appearance of shiny metallic specs - which will be bits of piston material from the effects of detonation.) If, after setting your total advance to about 35 degrees, you find you've got "the D word" you've got two choices at that point: 1) reduce the amount of timing until it stops (which is going to hurt performance and may cause the other problems you have, but at least it won't kill the motor) or 2) rebuild the engine to reduce the compression ratio (probably means new pistons with enough dish area).... or I guess you could leave it alone, park it, and use it as a museum piece. :grin2: ... but that's probably not what you want to do I'm guessing.

Is there any way you could post a phone video of it running at idle?

Bear


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## 67GTO400 (Apr 16, 2016)

Duel Carbs and cam will cause rough idle and low vac. your actually lucky to have 12". My 400 with cam is at 10".. Others gave good advise about tuning with vac gauge, but I also recommend an adjustable Vacuum Distributor Advance that you can adjust to the low vacuum and that's a whole other tuning issue, but well worth it... Good luck !!


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## irelandGTO (Oct 24, 2015)

Not much help from compcams, they said the magnum cams aren't good for vacuum. So I checked the timing chain and all is good spot on with the marks, put her back together and no oil to valves but 50 psi at filter pulled the filter (fitted 2 months ago and zero miles) totally blocked .New filter on and rockers nice and quiet.
Took her for a spin and although she pulls like a demon the pinging is very noticeable under load, which could be detonation because of the high compression but it's been like that since 2000 surely she would have blown before now, when I took the heads off the pistons were perfect just black, there was some pitting on the exhaust valves. I've tried advancing and retarding the dissy but it makes no difference, very jerky at low revs slight misfire and awful rattle under hard acceleration.
I fitted a couple of carbs spacers at the weekend which seems to have helped with the hot cranking issue.
She also drives real nice other than the engine problems, nice suspension kit fitted holds the road well and feels tight and responsive.
I'll be ordering a disk back timing light this week so I'll see what I can do with the timing.
Could it be the wrong springs in the MSD distributor causing the wrong timing?


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## irelandGTO (Oct 24, 2015)

I think our gas is 95 octane.


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## PontiacJim (Dec 29, 2012)

irelandGTO said:


> I think our gas is 95 octane.


Detonation, or pinging under load, WILL destroy your engine -or blow another head gasket. The cam in the car, coupled with your already high stock 10.5 compression is too much for 95 octane. You will need racing gas, 100 octane or better. Adjusting your timing will not cure the problem. Its when your engine is detonating and you don't hear it that you should be concerned with.

Most performance street and street/performance motors, with a typical performance camshaft and a Static Compression Ratio of 10.0-12.0:1, will have a Dynamic Compression Ratio in the range of 8.0:1 to 8.5:1. Any higher may result in detonation problems with pump gas. Dynamic compression ratio should not to be confused with cylinder pressure. 

There is a difference between "static compression" and "dynamic compression." Static is what the actual "squeeze" is, or 10.5 in your case. Dynamic compression is the true compression as measured against the intake valve closing after bottom center.

When your dynamic compression hits near 8.0 compression, you are about as high as you want on a street engine. You cam specs using the Wallace calculator puts your dynamic compression at 8.75. Wallace Racing: Dynamic Compression Ratio Calculator


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## irelandGTO (Oct 24, 2015)

I've been researching the detonation issue further and I came across water injection system, have any if you guys any experience of this. It could be a relatively inexpensive solution.


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