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Discussion Starter #1
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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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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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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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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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.
:agree

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.
:agree

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

http://www.gtoforum.com/f50/gto-tuning-setup-tips-13052/
 

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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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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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distributor

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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my67goat,

After you set the initial timing the car should be idling around 600 rpm, attach the vacuum advance and check the timing again for a small increase to verify the vacuum advance is working. Then run the car up to 2500-3000 RPM and verify the mechanical advance is working. You should be somewhere around 36 degrees.

The XE262H Comp Cam runs a 110 LSA which starves the engine of vacuum at idle,
 

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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.
Just curious Bullet, what is your compression and what octane fuel are you running? Too low of octane will defintely cause engine run-on, thus needing to retard your timing. I am not a performance expert, but could always run a lot more advance than 25 degrees in my pontiacs, mopars, and chevys.

Regarding the carb discussion for My67, I would ask your mechanic to spend a little time with Cliff's book, or the Carb Paper from LARS, and you will have a smooth running Qjet! It certainly seems that a high percentage of "off the shelf" Qjets have issues due to poor rebuilds.
 

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my57goat.... sounds like it's all over the place and it sounds to me like the mechanics you've talked to are really just guessing. It's time to go into "check one thing at a time" mode and start eliminating possibilities until the real cause presents itself.

1) Make sure you've got a good seal on the intake manifold gaskets. Get yourself a scan of that spray 'starting fluid'. Get yourself some kind of tach you can hook up and see while you're working under the hood. Remove the air cleaner so you can "get to" the intake manifold. Start it up and let it idle, then work around the edges of the intake where it meets the heads and spray a little starting fluid at the joint while watching the tach and listening. Does it speed up/smooth out when you spray? You've got an intake manifold gasket leak at that point. That's going to throw everything off on your fuel mixture - fix that before you go on to anything else.

2) Put a timing light on it and just watch the marks. Vary the throttle a little bit - take it up to around 3000 rpm - slowly. You should see the timing mark on the balancer move "away" from the TDC mark on the timing cover as rpm increases, and it should do so smoothly with rpm change. If it's "jumping around", you've got something loose in the advance mechanism or the distributor. It should also smoothly return to its original spot when you let it come back down to idle (slowly). If it's "sticking" you'll see it.

3) Get yourself one of those hand-held infrared probes (they're pretty cheap at places like Harbor Freight) and take a reading near the thermostat when it gets good and warmed up. Is it running hot? Normal?

4) Get yourself a vacuum gauge and see what it's telling you at idle. Most healthy street engines with mild cams are going to make well above 15" of vacuum - even above 20" or higher. Watch the needle - is it steady or is it fluttering? If it's below 15" and/or unsteady "without reason" (like a pretty rowdy cam in the motor) begin to suspect a valve train problem (bent pushrod, faulty lifter, improper valve adjustment, etc.). You can also use the vacuum gauge to get your idle mixture adjusted correctly.

5) Put a fuel pressure gauge on it to tell you how your fuel pump is making out. With a QJet you don't usually want more than 7psi at the inlet (sometimes a little less depending on which needle/seat/float you're running) but you don't want it to be low either (less than 3 or 4 psi). If your fuel delivery isn't consistent, suspect a problem with the pump or fuel line (clogged filter, tank sock, etc)

6) Pull the spark plugs and have a look at them. Lots of reference sites on the 'net to compare to for various problems. Start it up in an as dark as you can make it garage and have a look --- see any spark jumping around on wires in places where it's not supposed to be?

You can get there - something's causing it - maybe a combination of somethings. When you figure it out it'll all make sense.

Bear
 

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Look at the fuel pump or sock in tank
 

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Discussion Starter #17
Took the car out of storage yesterday. It was rainy and 39 degrees. Cold. Temperature gauge never got over 160 degrees. The car ran great. No problems what -so-ever! Idle was perfect, accelerated and shut down without over run and no dieseling either. So, I had the original carb with mechanical choke just rebuilt because I thought the electric choke carb was the source for all the problems. After my nice surprise yesterday, I'm beginning to think the problem was the hot, humid summer days here in Minnesota just cooking the gas in the bowl or causing vapor lock. Also, I only have one gasket between the manifold and carb base now (didn't know at the time of installation the 67 had a different set up) . Per Geeteeoh guys advise I'm planning on the metal shield sandwiched between the two gaskets for better heat insulation and dissipation. I really don't think I have vacuum or timing issues-I think all the problems were heat related. What do you think. And by the way, thanks guys for all your comments.
 

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I think absolutely your issues were heat related. I would do nothing more than install the heat shield between the base gaskets and go from there. My bet is that it'll be fine. "Don't fix it if it ain't broke!"
 

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Discussion Starter #19
Mr. Geeteeohguy, new problem today. Installed the rebuilt carb with mechanical choke and choke does not really want to open. My mechanic asked me if I want to put in a manual choke. Said NO! Also came up in discussion, will it help to change the intake exhaust port block off gasket. Currently it is blocked off and we could pull it off the intake and put in a new gasket not to block off the exhaust port. Then it should run a little hotter and open up choke. Right? So should the intake exhaust port be blocked of or not?
Thanks, Greg
 

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That's your problem. Especially where you are, up North. You need to run an unblocked intake for the factory choke to work. No gain on a street driven car with a blocked intake.....and a lot of poor cold/warm drivability problems, to boot.
 
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