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Old 02-03-2006, 06:45 PM
78transam 78transam is offline
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Off idle driveability problems

Hello. I have been trying to correct the drive-ability issues with my 1978 231 v6 firebird, all stock.

Ever since I had the car, It has been undriveable, it couldn't idle for more a few minutes, backfiring through the carb on WOT and stalling coming to a quick stop. Vacuum has always been low and inconsistent, the plugs fouled very quickly, with black smoke under load.

I just replaced the carb with a re-manufactured Rochester 2bbl, and noticed immediate improvement in the idle, with 15 in hg vacuum @ 900rpm.

My problem is this:
When I put the transmission in Drive the RPMs fall to 550 and vacuum drops to 5in hg, the engine wants to stall. If I SLOWLY increase the speed to 1000 RPM to keep it running vacuum goes to 0 in hg.

The engine doesn?t want to go much faster than 1000rpm in Drive/Reverse. If I get on it too quickly it cuts out. It hasn?t got enough power to drive up the driveway. Put it back in park, vacuum returns to 15in hg.

I have checked for vacuum leaks, and can?t find any. I cleaned the plugs when I changed the carb. The plugs are still going black and are gas fouled, but not as bad as they were. Choke is working properly. The plug wires are separated, and I have checked (with a timing light) for a spark on all cylinders.

I tried swapping the HEI coil for another, no difference. Also cleaned and checked rotor and distributer cap.

I tried advancing the timing (the vacuum gauge pointed to late ignition timing). Its base timing is now at 19? at 900 RPM. Slight improvement in idle quality but had no effect on my problem. I am running new 95 octane gas, with two fuel filters, both clean.

However I noticed, under the EGR blank off plate, the intake port was full of gas. I don?t know why.

Sorry to be so long winded but I have spent a few days working on this and can?t fix it. I just want to give you as much info as possible, so as not to waste your time.

Any help with this would be very appreciated. Thank you.
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