Re: [Chrysler300] timing and vacuum

["Laurence G. Johnson" <laurence_g_johnson@xxxx>]

John,
Ignition advance at idle has a dramatic effect on intake manifold vacuum. 
Most engines of this period need 8-12 degrees of static (initial) advance 
and should idle with 16-18 inches of mercury. Vacuum falls off to 6-10 
inches and the idle roughens as the timing is retarded. If the initial 
timing is too far advanced, the engine will appear to drag or even kick back 
on the starter while cranking.

I don't think that's your problem, however. Your post mentioned changing 
carburetors, installing the original WCFB's. These carbs had heat crossovers 
cast into the cast iron base plates in the vicinity of the front throttle 
bores. The original gaskets were asbestos-steel shim construction to 
withstand the heat and had cutouts to match the crossover passage. However, 
the cast passages had many different shapes and positions and the gasket has 
to match the specific carb. If the gasket and passage mismatch, or if you 
install them upside down, you will have a big vacuum leak and the engine 
will idle with low vacuum as a result.

Give that a look before changing the distributor.

Larry Johnson


> From: john_nowosacki@xxxx
> To: Chrysler300@xxxxxxxxxxxxxxx
> Subject: [Chrysler300] timing and vacuum
> Date: Mon, 4 Aug 2003 10:14:19 -0600
> Question for the mechanics in the group.
> Can ignition timing (distributor position) have an effect on measured 
> intake manifold vacuum?
> My 57 is running ragged after replacing the two silly Holley 2-barrels with 
> rebuilt original WCFB's.
> I know distributor may have been bumped over the winter, but I'm having 
> trouble locating either a mark on the balancer or markings on the metal tab 
> that used to have 0-5-10 (?) or 5-0-5 (?) labeling.
> I'm only measuring 10-12" of vacuum, and I think it should be closer to 
> 20".
> Car starts ok, runs at a fast idle, but seems to be running on less than 
> all 8 at low idle.
> Also, while I have your attention, exhaust gas from the passenger side is 
> significantly warmer (at tailpipe) than drivers side. (no crossover tube 
> in exhaust system, and same volume of air coming out each side).
> It was a long winter, so I changed (too) many things without being able to 
> restart after each to check progress. (pulled plugs to put new valve cover 
> gaskets on, pulled old Holleys to put on freshly rebuilt WCFB's, relocated 
> coil and wires to proper position to make room for air cleaners, etc.)
> Any help/suggestions appreciated.
> If timing is too far advanced, and cylinders fire perhaps a tiny fraction 
> before intake valves are closed all the way, I assume that would reduce 
> vacuum, or am I over complicating things and the WCFB's are the most likely 
> culprit?
> It should be simpler than this. It's just fuel and air in the right ratio 
> at the right time!
> John

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