Help please...surging engine...

[007]

My AMC 304 all of a sudden idles poorly and surges from 400-1000 rpm while idling. It's decent in the road but as you slow and stop it dies unless you feather the throttle. You can almost hear it run on just a few cylinders when nearing a stop.

New plugs. New ECM. New fuel filter. New guts in tank.

I'm lost an so about to set this thing on fire...

But it probably wouldn't burn.

 

[mtnwhlr]

Sounds like the carb maybe time for a rebuild.

 

[Torxhead]

I would agree with Mtnwhlr with a possible carb issue. You say that you have a new ecm, would that be computer for a fuel injection or an ignition control module for the old prestolite ignition?

 

[jasonmark1993]

First thing I would do is play around with the mixture screws to see if that will even make a difference. Might need to adjust the idle screw up a bit so it will hold an even rpm while you do this.

Once its holding an rpm, even if its 1200 or something, do the carb cleaner test around the intake and base of carb. You may have good vacuum on a gauge but still be leaking.

Need to check the timing too.

I know the timing and mixture shouldn't be off if you didn't adjust them, but it helps with the diagnosis.

Take a look into the carb with it running, if fuel is dripping down in there due to high fuel pressure or high float or whatever, you can get surging.

 

[007]

I would agree with Mtnwhlr with a possible carb issue. You say that you have a new ecm, would that be computer for a fuel injection or an ignition control module for the old prestolite ignition?

For the Prestolite...

 

[007]

First thing I would do is play around with the mixture screws to see if that will even make a difference. Might need to adjust the idle screw up a bit so it will hold an even rpm while you do this.

Once its holding an rpm, even if its 1200 or something, do the carb cleaner test around the intake and base of carb. You may have good vacuum on a gauge but still be leaking.

Need to check the timing too.

I know the timing and mixture shouldn't be off if you didn't adjust them, but it helps with the diagnosis.

Take a look into the carb with it running, if fuel is dripping down in there due to high fuel pressure or high float or whatever, you can get surging.

Will do. Could this be a distributor / advance issue by any chance?

 

[jasonmark1993]

Its possible something came apart in there and its causing the timing to be far enough off that its surging.

You might just be running lean too. Id def. start at the carb to see if it responds to adjustments.