Helping a friend with a 427/425 that we put a MSD dist and spark box in. The problem is according to the MSD graph, the mech. advance starts at 0 rpm and is about 4 degrees at 1,000rpm. So when setting the timing at 850, there's apparently already a little mech. advance in.OK now when you blip the throttle, you get more mech. advance which in turn wants to cause the engine speed to increase which won't let the mech. go back to where it was. Therefore the idle is now up around 1100 and will slowly (~30-40 seconds) come back to 850. All of the MSD springs show this same amount of advance at 1,000 rpm. Any ideas??? [sm=dontgetit.gif]

 

Iwould try putting stiffer springs or lighter weights in. If you cant get it right, try bringing it to a speed shop with a distributor machine, they will be able to set it up so it comes in exactly where it should

-Rich

 

Tried that but all of the MSD spring graphs show mech advance starting a zerorpm and reaching about 4 degrees at 1,000 rpm. Since with the cam we've got, we are idling at about 900 rpm, can't see how once the engine goes above idle, it will ever return since the advance has kicked in.

While it will slowly (~20 seconds) return to the idle setting when in the driveway, when we take it out and drive it, it wants to idle at about 1,100 rpm.

 

what about the weights? could you possibly put a lighter weight on or grind down the weights that came with it?

-Rich

 

Hi 73shark, if your using a Rochester carb, is the power valve working properly or hanging up? PG

 

Running an original Holley. We finally bit the bullet and put a stronger spring in so the advance doesn't start at idle and all's well now. Finally convinced him that on the last dyno run a couple of years ago, it didn't appear that the secondaries were fully opening. Put the next lighter spring in and it goes like the proverbial raped ape now.

Thanks for the tips.