Engine Run-on After Shut-off

[Tony H.]

What could be causing my 1970 454 to continue to run after shutting off the ignition? The engine reached normal operating temperature and took about 5-10 seconds to shut itself off after removing the key from the ignition. Also, while driving, the engine has little power and a lot of hesitation. When I shut it off a second time without the air filter lid on, a mini gyser of gas spewed up before the engine coughed and shut off. Please help!

Otherwise I'm ready to go to Pittsburgh in ten days.

Tony

[James F.]

Re: Engine Run-on After Shut-off

Tony, I know nothing about big blocks! Something inside the cylinder is hot ennough to allow the engine run-on, it's acting like a glow plug. Make sure the carb throttle plates are closing in the carb bore when the engine is shut off. Sounds like they are open slightly, enough to allow enough some air to be pulled in and gas along with it. Check your iginition timing (I would do this first). The backfire through the carb usually indicates a lean condition. Also check for vacuum leaks on any fittings that go into the manifold or the carb base. If this run-on continues to be a problem until you find the cause, you can shut off the engine with the transmission in gear and let the clutch out at the same time (if it's a manual). Hope some of this helps.

[James F.]

Re: Engine Run-on After Shut-off

Tony, I know nothing about big blocks! Something inside the cylinder is hot ennough to allow the engine run-on, it's acting like a glow plug. Make sure the carb throttle plates are closing in the carb bore when the engine is shut off. Sounds like they are open slightly, enough to allow enough some air to be pulled in and gas along with it. Check your iginition timing (I would do this first). The backfire through the carb usually indicates a lean condition. Also check for vacuum leaks on any fittings that go into the manifold or the carb base. If this run-on continues to be a problem until you find the cause, you can shut off the engine with the transmission in gear and let the clutch out at the same time (if it's a manual). Hope some of this helps.

[roger Coen]

Re: Engine Run-on After Shut-off

Gary,

Something is causing the engine to fire when the wrong valve is open, result-backfire. It could be anything from moisture in/on plug wires, distributer wet to bent valves. One things sure, get it fixed ASAP. Post before had some good possibilites too.

[roger Coen]

Re: Engine Run-on After Shut-off

Gary,

Something is causing the engine to fire when the wrong valve is open, result-backfire. It could be anything from moisture in/on plug wires, distributer wet to bent valves. One things sure, get it fixed ASAP. Post before had some good possibilites too.

[Tony H.]

Re: Water Injection Cleaning of Intake

I'm wondering whether water injection cleaning would improve the problem I am having with engine run-on after ignition shut-off. What is the procedure to properly carry out this cleaning method? I'll be checking the timing out this afternoon. I'll keep the board posted on findings.

[Tony H.]

Re: Water Injection Cleaning of Intake

I'm wondering whether water injection cleaning would improve the problem I am having with engine run-on after ignition shut-off. What is the procedure to properly carry out this cleaning method? I'll be checking the timing out this afternoon. I'll keep the board posted on findings.

[John]

Re: Water Injection Cleaning of Intake

Water injection would probably do a marginal job. Why not have it done professionally with a carbon vac machine. Not to expensive and you will get better results.

[John]

Re: Water Injection Cleaning of Intake

Water injection would probably do a marginal job. Why not have it done professionally with a carbon vac machine. Not to expensive and you will get better results.

[Tony H.]

[Tony H.]

[Joe L.]

Re: Engine Timing for 1970 BB?

Tony----

The proper setting for your engine is 6 degrees BTDC. Hot idle RPM is 600 with TurboHydramatic and 700 RPM with 4 speed. I'd set the timing and carburetor adjustments according to the procedure specified on the emissions label. For your car, the proper label is GM #3980210 coded "DQ". If you don't have the correct label, you can get one from many of the Corvette vendors. They have not been available from GM for years.

[Joe L.]

Re: Engine Timing for 1970 BB?

Tony----

The proper setting for your engine is 6 degrees BTDC. Hot idle RPM is 600 with TurboHydramatic and 700 RPM with 4 speed. I'd set the timing and carburetor adjustments according to the procedure specified on the emissions label. For your car, the proper label is GM #3980210 coded "DQ". If you don't have the correct label, you can get one from many of the Corvette vendors. They have not been available from GM for years.

[Joe L.]

Re: Water Injection Cleaning of Intake

Tony----

I don't know that I'd try "water injection cleaning". However, you might try GM Top Engine Cleaner. This GM #1050002(16 oz can) or GM #12345089(13 oz aerosol). Use them according to the instructions on the container. I have had success with these products in removing combustion chamber deposits.

[Joe L.]

Re: Water Injection Cleaning of Intake

Tony----

I don't know that I'd try "water injection cleaning". However, you might try GM Top Engine Cleaner. This GM #1050002(16 oz can) or GM #12345089(13 oz aerosol). Use them according to the instructions on the container. I have had success with these products in removing combustion chamber deposits.