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post #1 of 21 (permalink) Old 04-06-2016, 11:34 AM Thread Starter
 
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Gto trouble

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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post #2 of 21 (permalink) Old 04-06-2016, 12:15 PM
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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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post #3 of 21 (permalink) Old 04-06-2016, 01:12 PM Thread Starter
 
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Carbs are fine just put a rebuild kit in both, no choke on either carbs.
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post #4 of 21 (permalink) Old 04-08-2016, 07:53 PM
 
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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/...404_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.
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post #5 of 21 (permalink) Old 04-09-2016, 02:27 AM Thread Starter
 
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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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post #6 of 21 (permalink) Old 04-09-2016, 05:38 PM
 
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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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post #7 of 21 (permalink) Old 04-09-2016, 10:26 PM
 
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Originally Posted by irelandGTO View Post
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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post #8 of 21 (permalink) Old 04-10-2016, 03:05 AM Thread Starter
 
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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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post #9 of 21 (permalink) Old 04-10-2016, 12:28 PM
 
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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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post #10 of 21 (permalink) Old 04-10-2016, 01:04 PM Thread Starter
 
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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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