Big drop in idle when fans kick on???

[Pman1961]

Dana I have the common MSD 85805 I believe mechanical advance. I checked initial timing at 1100 rpm and was 18 degrees with 34 total advance. When fans kicked on or I lowered idle to around 800rpm the initial timing was 10 degrees. So it appears it is idling with initial advance and makes since when rpm drops the timing retards and continues to drop rpm. Called and talked with an employee with KCR. I did a test this evening as he suggested to see if the car idled better. I was asked to set the initial up to 26 degrees advance then lower idle, turn on fans and see what happens. I set initial at 26 degrees, lowered idle to 1100 rpm, turned on fans and the rpm dropped maybe 25 rpm and held. So I took the bushing out at the mechanical advance and it appears to have blue coloring and measured .340. I've sent him an email this evening of my findings to see what I should do next. Until tomorrow!

[Dana E.]

Perry,

it looks like the blue bushing is the standard one that comes with that distributor and is supposed to be good for 21 degrees mechanical advance. They make a black colored bushing (the largest one they list in the instructions) which is good for 18 degrees advance. Theoretically you should have 16 degrees initial and 34 total. 18-20 degrees initial timing would be better, but you can see what happens with 16 degrees. You may still end up having to make a bushing, or welding up the slot where the bushing rides.

It also sounds like someone installed the two lightest (silver) advance springs since the advance starts below 1000 rpm. You need to slow down the start of the advance curve-something like 1200 rpm. I would install the largest (black) advance bushing, replace one of the light silver springs with one blue one and see how that works. This should be the kit you need:MSD Ignition 8464 - MSD Advance Kits - Overview - SummitRacing.com

Dana

This scenerio is one reason why I like the Mallory Max Fire distributor: plug in the laptop (or remove the distributor cap), set the rev limiter, chose one of the factory preset curves, or design your own mechanical and vacuum advance curves, and you're done. Best of all: no MSD box to leave you stranded....knock on wood.

[Pman1961]

Dana...I just found a website called 4secondsflat.com that sells 10 and 14 degree bushings for the MSD distributor. My car likes a lot of initial timing at idle with my cam. Currently I'm 16 initial and 34 total. Been considering locking the distributor and using the msd starter saver but am going to try the 10 degree bushing first.

[Dana E.]

How big is the cam in your motor (duration at .050")? 20-22 degrees initial timing should be enough to make it idle good. Don't waste your money trying to lock out the distributor and using that starter saver.