timing advanceing at higher RPM

markyb

markyb

Senior Member
Any thoughts on this? Not that I see it as a problem, just surprised that with a stock distributor and modern points plates that it would advance like this. I can't get my mind around how this happens other than at higher RPMs a stronger spark is jumping to the distributor cap contacts slightly sooner?

http://www.youtube.com/watch?v=eNmTQPS1Y6A
 

Likely not the dizzy at all.

Propagation delay in your combo digital timing/strobe device? Fancy does not equal accurate.

Increased oil pump load shifting the cam (via the helical drive gear)? The cam shaft is walking.
 
I can see the cam walking making this happen, especially since the amount of advance peaks after a certain level of RPM.

Propagation delay should be constant, therefore, any delay of the strobe shouldn't increase with rising frequency of the strobe?
 
The short answer is:
Model A Fords and timing lights are allergic to one another..;)

My guess is cam walk...but I really have no clue.
 
Mitch//pa said:
In your video 3 ATC is advanced not retarded
Click to expand...

yes, although at idle it is about 3 degrees after TDC, then as I raise the RPMs it advances to about 3 degrees BTDC with the spark lever fully retarded. My most recent timing is set with Marco's method, I like that since it can be done anywhere with just a few tools and the hand crank. I have not put the timing light on it yet to see how that setting registers at idle, but the engine runs good now.
 
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