Engine Sputters when turn the car off

[minifridge1138]

Hey everyone,

I was driving today and noticed something new: when i turn the car off it sputters a bit and tries to keep running before it finally stops.

It doesn't do this all the time.

I thought it might be the ignition timing, so I re-set it to 8* btdc.

The only things I can think of are:
1) timing is still wrong
2) mixture is too lean.

Any suggestions would be appreciated.
Thanks!

 

[TJay]

It can be caused by a number of things, timing you have looked at and you are right about a lean mix.

Also things like low octane fuel, wrong tempeture plugs will also cause it. I don't know what region you are in, but winter gas in warmer weather is another cause. These are only a few that create run on or sputter.

Good Luck

 

[snr8715]

More than likely it is idled to high.

 

[gmjunkie]

More than likely it is idled to high.

That would be a good possibility!!!

 

[Kid_Again]

did you do anything to the car recently?

you brought the timing back to 8*..from what, 10*?

may just be the gas

 

[JohnZ]

Primary throttle blades are too far open at idle; disconnect the cable from the carb lever and see if it idles down and shuts off without dieseling. If it doesn't diesel any more, re-adjust the throttle cable so it doesn't hold the throttle open, and re-adjust the idle mixture screws for highest steady vacuum.

 

[wishuwerehere82]

Most likely it's related to the high idle problem you posted earlier this week.
Probably the throttle is sticking open when the run-on happens.

 

[minifridge1138]

I'm still trying to figure out why the throttle is sticking.
It doesn't seem to be anything with the linkage.

To be honest, carburetors are still relatively new to me.

Also, it doesn't diesel when i shut it off with the vacuum advance disconnected.

My base timing is set at about 8* and with the vacuum advance I get 30* at idle.

I have only done 2 things recently to the engine:
1) i switched the vacuum source for the advance from ported vacuum to manifold vacuum.
2) i accidentally filled the car with regular instead of premium.

 

[gmjunkie]

I'm still trying to figure out why the throttle is sticking.
It doesn't seem to be anything with the linkage.

To be honest, carburetors are still relatively new to me.

Also, it doesn't diesel when i shut it off with the vacuum advance disconnected.

My base timing is set at about 8* and with the vacuum advance I get 30* at idle.

I have only done 2 things recently to the engine:
1) i switched the vacuum source for the advance from ported vacuum to manifold vacuum.
2) i accidentally filled the car with regular instead of premium.

You have the vacuum advance on the wrong port!! There shouldn't be any vacuum on the advance at idle!!

 

[JohnZ]

As I indicated earlier, there are many advantages (driveability, cooling, stable idle, throttle response, fuel economy) to having full manifold vacuum on the vacuum advance - "ported" vacuum was an emissions "crutch". If you have 8* advance with it disconnected and 30* when you connect it, your unit is giving you 22* additional, which is excessive. You want a vacuum advance unit that supplies 15*-16* of advance when fully-deployed like the '63-'74 cars had.

The tank of regular probably didn't help any either, although if your '81 has stock compression, it shouldn't matter.

 

[minifridge1138]

I'll head to the auto parts store and get a different vacuum advance.

I also replaced the throttle return spring and that seems to have solved my excessive idle.

Thanks for your help!

 

[minifridge1138]

the new vacuum advance solved the problem.

Thanks for your help!

 

[Mr. Chuck]

After Running

Hey everyone,

I was driving today and noticed something new: when i turn the car off it sputters a bit and tries to keep running before it finally stops.

It doesn't do this all the time.

I thought it might be the ignition timing, so I re-set it to 8* btdc.

The only things I can think of are:
1) timing is still wrong
2) mixture is too lean.

Any suggestions would be appreciated.
Thanks!

My 81 was doing the same thing until I had the Carb rebuilt & adjusted to spec by local repair shop. Found that original throttle sensor and other components had seen better days (worn-out), replaced same, she now runs like or better than new. My problem became an issue when she failed to pass CA smog. Hope this helps!