Dies when slowing down

rivcokid

rivcokid

Senior Member
Ugh! I'm stumped. The car runs and idles fine, except when i remove my foot from the throttle to slow down, or when just slowing down, it sputters and dies more than half the time. It will start right back up again. I can overcome this by keeping the throttle advanced, but then I'm grinding gears.

I replaced the gasket to the carb, which cured a problem on my other car of getting too much air. I've cleaned the carb out and the fuel line. When I try to adjust the idle screw, when I turn it out, the engine will sputter, but I can turn it all the way in and no dying like it should. In fact, there seems to be no difference in the idle from fully in to mostly out. I pulled the idle screw out to take a look at it and it appears to be just fine - no marks, no curves, no misalignments that I can see.

The car idles fine standing still, and runs fine too.

I should note that this is a 31 town sedan, stock, with a Zenith carb.

Thanks (again) for your help!
 
The way you describe the idle mixture screw adjustment, it sounds to me like it may be a little too lean. With the screw all the way in and the throttle closed, you are shutting off the air for the idle circuit.

By "keeping the throttle advanced", you are no longer on the idle circuit.

I would suggest checking the throttle shaft clearance. It could be sucking air in at the shaft even when the throttle plate is closed. This is an often overlooked source of a vacuum leak. I put a dab of EZ Turn Lube on my shafts when installing.

Oversize shafts and bushing are available.

Might also check the float level. may be too low.
 
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Another possibility is a vacuum leak - maybe intake manifold/block interface or windshield wiper line (if equipped with a vacuum motor). Please share the fix when known.
 
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My vacuum wipers did not work properly so I plugged the intake manifold port for the vacuum line and my engine settled down and ran smoother. Too lean at idle with wiper line attached.
 
Thanks all - after this next storm I'll go and see if I can find the leak. I will definitely post a solution if/when I find it! Thanks again
 
I had the same problem and i figured it out by letting the car coast to a stop without using the brakes. When I found that it did not die when I did that I thought maybe the fuel was sloshing to the front of the bowl starving the engine for fuel. Was I right? I can’t say I only know that when I raised the float level a bit the problem went away.
 
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