henryk8398

I've been trying to chase down a dieseling issue for a long time. Finally, I discovered a place that some may have overlooked; the connector to the Thermal Vacuum Valve on the air cleaner. The holes on rubber connector had stretched too far, causing a small leak and forcing the ILC plunger out. This one drove me nuts! Anyway, I plugged the connector since the preheater doesn't do me any good in the desert. Everything is fine now, but I had to readjust the carb mixture. I ended up having to turn each idle mixture needle in (leaner) by 1.75 turns to get the dwell near 30. That's pretty significant. I'm willing to bet that will help my gas mileage, too! Just wanted to pass on a nugget of wisdom to anyone that's looking for vacuum leaks on their 307 beast!

rustyroger

Thanks for sharing that one, I guess that might well apply to many other cars as well.

MDchanic

The idle mixture screws shouldn't affect the dwell angle. You should only be able to change that by adjusting the points gap.

- Eric

rocketraider

83 Ninety Eight will be a CCCC system with electronic Q-Jet, so yes, it could affect it.

TripDeuces

Why would dwell change on this? Dwell in an HEI is electronically controlled by the ignition module. Just want to know why changing the mixture screws effects it?

Lady72nRob71

Yes, 83 uses the CCC and electronic Q-jet.
My guess is he used a dwell meter hooked to the mixture control solenoid and adjusted mixture until solenoid was running at around 50% duty cycle.
There is a lead laying on top of the engine for this purpose and this is actually the way the FSM instructs.
So this is not ignition dwell...

MDchanic

Ohhhhhh... Not the points dwell angle, which is an angular measurement of duty cycle, but the actual duty cycle of the mixture solenoid as measured by a points dwell meter.

I see. Never mind.

- Eric

Lady72nRob71

At least repair shops (and us DIYers) were able to find a new use for their aging dwell meters and not have to replace them with a new costly "CCC carb mixture control solenoid duty cycle" meter that did the same function...