Help me timing or carb issue - Pontiac GTO Forum
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post #1 of 20 (permalink) Old 09-16-2012, 09:18 AM Thread Starter
 
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Help me timing or carb issue

67 GTO original 400 complete carb to pan rebuilt and the TH 400 rebuilt with mild shift kit and installed in June this year. Just over 750 miles on it now.
Had it built with KB pistons dished.
Compression as measured by machinist at 9.3:1.
Comp cam 262
After rebuild had removed original Qjet and had another qjet rebuilt with electric choke.
30 over. New water pump, balancer, fuel pump.
new springs, cam. Heads 670 3 angle valve job, hardened valve seats.
crank reground with new bearings rods, etc.
engine was lined honed, balanced, torque plate used, turned out great.
New torque converter stock, new flex plate.
New plugs plug wires, petronix igniter II, new coil. new battery.

Originally car runs great when warm but would bog down when you get on it. Mechanic suggested a new carb rebuild, (everything else has been rebuilt) that is why I chose the electric choke qjet that could be bolted on the original intake with no modifications or adapters.

With both carbs car would start then stall after I would put it in gear this would happen about 2,3 or 4 times so I would just sit and let it warm up for about 3 to 5 minutes. I would drive to the nearest stop sign and it would stall. It is rough at idle and stall. Mechanic monkeyed around with idle and mixture setting. I would need to keep reving up in nuetral to keep it going. We ended up setting the idle high so it wouldn't just stall out. Once the car is warm it runs fine has good acceleration. Still is mildy rough at idle sitting at stop lights, although idles a little high.
My mechanic said bring it back to carb shop and have em fine tune it. But now a new problem is developing. It wants to increase idle on its own. At the stop sign the engine started to rev up a little and I didn't even need to put my foot on the gas and I was cruising up to 30 mph. Also, the initial timing is 10 Degrees and 36 final degrees. Carb shop said you may have vapor lock. Fuel line sits right on top of intake manifold. So, somebody thinks its vapor lock, one thinks it is timing and one thinks it could be a vacum problem, one thinks its the carb. Can Anybody help. Thanks Greg
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post #2 of 20 (permalink) Old 09-16-2012, 09:43 AM
 
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did you replace all the old rubber gas lines (including section in back near the tank?), they will get small cracks in them and suck in air bubbles. Troubleshooting 101 start with the simple things. Gas filters changed out? Sock in your fuel pickup cleaned or replaced. 10 degrees is a a little low on initial timing. Sure some of the carb guys will have some hints on that but first make sure everything leading to the carb is good to go.

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post #3 of 20 (permalink) Old 09-16-2012, 02:11 PM
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6 degrees is the spec for initial timing on a '67. But that's not the problem, IMO. Neither is it vapor lock. Vapor lock will cause a stall out and it won't re-start until it cools off, usually after some time. I think you have a vacuum leak....at the intake runners or at the carb base. Since the problem occurs with both carbs, this suggests a non-carb related problem. Check for vacuum leaks. The rough running, hesitation, and stall out suggests an over lean condition. I would also go back to the original, thermally operated choke set up. A competent mechanic should be able to do a power balance and vacuum check to determine the source of your drivabiltiy issue. Good luck.
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post #4 of 20 (permalink) Old 09-16-2012, 03:42 PM Thread Starter
 
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Today I took it out for a drive. Pumped it 2x and started right up. Let it warm up a few minutes and drove away feeling fine. Went to hardware store with no problems and even got on it a little. Came out after 10 15 minutes and it was very hard to start, I pumped it 1x and seemed to flood, I held the pedal to the floor and it sputtered and started up after cranking a few turns. Then as I drove away it seemed to idle up on its own again. When I got home and turned it off. It labored to shut down. Now, here I am asking for more advise.
Thanks, Greg
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post #5 of 20 (permalink) Old 09-16-2012, 03:44 PM
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Quote:
Originally Posted by Instg8ter View Post
did you replace all the old rubber gas lines (including section in back near the tank?), they will get small cracks in them and suck in air bubbles. Troubleshooting 101 start with the simple things. Gas filters changed out? Sock in your fuel pickup cleaned or replaced. 10 degrees is a a little low on initial timing. Sure some of the carb guys will have some hints on that but first make sure everything leading to the carb is good to go.


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Originally Posted by geeteeohguy View Post
6 degrees is the spec for initial timing on a '67. But that's not the problem, IMO. Neither is it vapor lock. Vapor lock will cause a stall out and it won't re-start until it cools off, usually after some time. I think you have a vacuum leak....at the intake runners or at the carb base. Since the problem occurs with both carbs, this suggests a non-carb related problem. Check for vacuum leaks. The rough running, hesitation, and stall out suggests an over lean condition. I would also go back to the original, thermally operated choke set up. A competent mechanic should be able to do a power balance and vacuum check to determine the source of your drivabiltiy issue. Good luck.


Here is a thread started by Lars, he states 90% of carb problems are actually timing problems, Good luck

https://www.gtoforum.com/f50/gto-tuni...up-tips-13052/

Randy


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post #6 of 20 (permalink) Old 09-16-2012, 04:12 PM
 
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Metering rods

Sounds like you have idle circuit in carb problem timing is usually an issue but if it's an on off issue carb is first place I would ck after you eliminated all other areas if it were timing it would be a constant issue did you rebuild the carb that's on it now take it back to whoever built it and get them to fix it ck the intake runners for vacuum leaks what happens when you run the mixture screws in does it affect the car ? run one side in and then back out until eng runs smooth as you can get it then do the otherside general rule of thumb run them in back out 2 1/2 turns than fine tune it just my 2 cents hope it helps used to build q jets for a living ..
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post #7 of 20 (permalink) Old 09-16-2012, 04:39 PM Thread Starter
 
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So is it 6 degrees or 10 degrees as mentioned in the above posts? Thanks
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post #8 of 20 (permalink) Old 09-17-2012, 11:19 AM
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So is it 6 degrees or 10 degrees as mentioned in the above posts? Thanks
With the vacuum advance line unplugged and the port capped it is 6 degrees BTDC. CA (A.I.R.) manual transmission car is 4 degrees ATDC

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post #9 of 20 (permalink) Old 09-17-2012, 06:39 PM
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Also, timing CAN be intermittent. I had it happen on my '65: I was getting fast idle and hard cranking every now and then.....turns out the mechanical weights on the distributor were staying in the advanced position due to a gummed up distributor shaft. Removed and cleaned up the distributor, and all is well. The devil is in the details...
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post #10 of 20 (permalink) Old 09-17-2012, 07:35 PM
 
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distributor

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Originally Posted by geeteeohguy View Post
Also, timing CAN be intermittent. I had it happen on my '65: I was getting fast idle and hard cranking every now and then.....turns out the mechanical weights on the distributor were staying in the advanced position due to a gummed up distributor shaft. Removed and cleaned up the distributor, and all is well. The devil is in the details...
If you got 36 deg of total timing at a fast idle you got a dist. problem. I've got a 455 550 horse and my total timing is 25 deg. Any more and it want's to keep running when you shut it off.
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