RPM rate returning to idle

[kent olsen]

This one I don't understand.

First this is a 2.7L with "E"Cams, webers, pertronics and MSD.

If I'm running along at say 3000 RPM, put the clutch in and take my foot off the gas the RPM drops down to about 1800 RPM and then slowly (about 10 secs) returns to an idle of about 1100 RPM, which is where I have it set.

The return springs are ok. What causes the engine to not drop all the way down to 1100 RPM?

[Steve@Rennsport]

Kent,

I'd be looking at a sticky throttle linkage (bushings at bellcranks) as well as thinking about sticking advance weights.

[304065]

What Steve said. I had a hanging idle at 2K, sent the Diz to Barry Hershon, he said both springs were rusted and the phenolic insulator plate had "cracked in a million pieces."

[kent olsen]

I'll have a look at the advance weights, althought the distributor was rebuilt about three years ago.

[Eagledriver]

I had a set of carbs that would do this. The idle circuit was very poor so the car would suck extra gas through the idle circuit on overrun then gradually idle down when the gas was burned away. I sold the carbs to someone else and bought PMO's.

-Andy

[Steve@Rennsport]

Originally Posted by kent olsen

I'll have a look at the advance weights, althought the distributor was rebuilt about three years ago.

They still need maintenance and that means removing the rotor to drip some motor down the center of the shaft a few times a year.

That lubricates the weights to help keep them from sticking.

[304065]

See Warren's famous distributor lube thread for more on this.

To REALLY do the job right you must remove the tiny circlip on top of the distributor shaft so the advance mechanism can be removed. Once inside, you will find the weights pivot on a phenolic plastic plate which wears over time due to the sliding action of the weights. This can be replaced by a piece of teflon to make the weights slide easier. Likewise the advance mechanism rusts and will hang up.

There is SOME information on this website about the proper order of the many small washers, insulators and whatnot contained in the distributor, but to really do it right requires the services of a professional who can knock the pin out without destroying the gear, remove the distributor shaft, replace any required washers, shims and spacers, clean the advance weights, replace the rubbing plate, change the springs if necessary (old springs lose their tension, causing the distributor to advance too far and too soon), bead-blast the housing and assemble everything. THEN put the distributor on a machine (not common these days) to verify the advance settings.

It's a lot of work for the amateur.

[kent olsen]

Thanks all

Looks like I'll try some lube for the weights and also lube all the bellcranks and connections along the throttle linkage.