Fi distributor

[Clem Z.]

Re: Fi distributor

Not sure I know what to look for. Doesn't it have to be at the #1 terminal if I can get the timing light indication at idle and at speed? It has to be there right??

the rotor tip moves in relation to the cap terminal as the distributor advances. see where it is at at full advance. i know nothing about the petronix unit but but converting to a magnetic pickup with the MSD is what a lot of race distributors use.

[Clem Z.]

Re: Fi distributor

the rotor tip moves in relation to the cap terminal as the distributor advances. see where it is at at full advance. i know nothing about the petronix unit but but converting to a magnetic pickup with the MSD is what a lot of race distributors use.

i have used the GM corvette TI pickup distributor with MSD in lots of race engines. a lot of after market dist use the ford pickup with a MSD

[William C.]

Re: Fi distributor

No, as long as the rotor tip is pointing to the post that has the number 1 plug wire attached to it OK, that can be any post in the cap, although there is a "standard" configuration used at the factory. Have you checked the advance curve at the balancer with a timing light to see if the spark is advancing correctly, and that indeed you have a spark at the RPM at which your trouble is seen?


let's to thru what you have told us so far:
Timing is set at idle with a timing light and is ok
as rpm increases "popping" sound is heard in the exhaust, ASSUMED to be distributor related
Points have been replaced with a electronic gismo of unknown performance
Timing is ok on marks, I don't know how to interpret your last post as you don't reference a specific connection to the #1 plug wire, but if that is your reference then the "tooth off" becomes irrelevent, as mentioned, the major significance of that is to assure the vacuum advance has appropriate "swing" to set timing, not an issue with non-vacuum advance dist.

Based on the above information, if I'm understanding it correctly, I would replace the electronic gizmo with a set of points and condensor to see if the problem goes away or stays. If it weren't an FI car, I'd say just drop in another distributor, but less practical for a fuelie unless you have a spare FI distributor available...

[Clem Z.]

Re: Fi distributor

i would guess you could also replace the MSD box as something could be going haywire in there in the electronics. this should help you use up some of your spare time checking out all these things

[Jerry G.]

Re: Fi distributor

Checked all wires and they are good and solid. I have 21 degrees advance at 1600 RPM. I used two different timing lights one with dial back and one without to verify settings. As i move distributor to advance I get to a very definite and repeatable point where the motor just dies. is it possible to advance too much and the motor dies. i would have expected sputtering if it was advancing too far. The petronix has posts that go up through rotor cap to insure proper indexing. The rotor tip is indexed by the square and round pins in the footballs isn't it. Total advance appears to be approx. 32 degrees.

[Michael W.]

Re: Fi distributor

Checked all wires and they are good and solid. I have 21 degrees advance at 1600 RPM.

A V8 engine fires every 90 degrees of crank rotation which translates to 45 degrees of distributor rotation. My guess is that as you exceed 21 degrees of advance, the spark that you wish would go to #1 plug is now heading off to the next cylinder scheduled to fire, which is number 8.

[Jerry G.]

Re: Fi distributor

So does that mean that there is a maximum initial timing that you can have?

[William C.]

Re: Fi distributor

I think Michael has forgotten that 1 degree in the distributor=2 degrees at the crank, so, unless I misunderstand, it should not be a problem, The FI distributor adjusts initial advance by rotating the top section of the distributor, rather than the base There may be a limit to initial advance but generally at the point it is reached, the engine will be difficult to start to to the charge firing too far ahead of tdc causing a "kickback". Certainly initial timing in the 12degree area is not unusual in the era we are talking. If you have a spare points-type distributor, I'd sure give it a try. This is why I'm not generally in favor of Black-box "Magic improvements" in 50 year old cars. My two FI cars still run fine with points, and I can tune the advance curve to anything within reason that I want. Is the centrifugal advance locked out in this distributor and the electronic unit provide the advance, or does the electronics just replace the points?

[Jerry G.]

Re: Fi distributor

All advance is mechanical. With 5 degrees at 1500 and 22 at 6400. Initial advance is approx 16 for total of 38. The MSD box is dumb, just spark. I have to do track testing tomorrow. I have a spare distributor but it's an identical setup.

[Michael W.]

Re: Fi distributor

I think Michael has forgotten that 1 degree in the distributor=2 degrees at the crank, so, unless I misunderstand, it should not be a problem,

No, you're right Bill, my post drifted between the crank degrees and distributor degrees which just confused the subject. At this point I'd bypass the magic MSD box and see what happens.

[Joe C.]

Re: Fi distributor

Make sure the air gap between the magnetic ring and the pickup is set properly. Do you have a Pertronix II unit? If so, then the gap should be between .010 and .040. If there is too much end play in the distributor main shaft, then when the shaft travels upward while running, the gap will grow to unacceptable size and cause misfiring. If your distributor was set up with a large amount of end play, then the proper way to set the air gap is by lifting the rotor/autocam/springs and weights/mainshaft mechanism to its full extended position before setting the air gap. When I set up distributors, I like to set the shaft end play to .001 - .002. Spec calls for max .008. If this is done, then one can safely set the air gap at about .015.

If the engine dies when you rotate the distributor head past a certain point, then it's possible that there is too much play in the interface between the head and the housing, which is affecting the air gap when rotated past a certain point, or, that one of the 2 wires to the pickup is chafed and shorting somewhere. Intermittent/weak spark will cause incomplete combustion and afterfiring.

[Jerry G.]

Re: Fi distributor

Thanks Joe. I like the idea of the rotation causing too much gap and ignition dying. That fits what I'm seeing. Don Baker set up the distributor so I'm sure the end play is well within specs. it is a petronixII. I'll check air gap.

[William C.]

Re: Fi distributor

I'm with Joe, be interesting to see what you get if you swap in the spare distributor, sure sounds like something is getting out of whack as the plate moves.

[Clem Z.]

Re: Fi distributor

i would start with switching out the MSD as it would be the quickest and easiest to do

[Jerry G.]

Re: Fi distributor

OK, well after thinking through several of the ideas offered here and talking with experts this is where we ended up. My problem was with the distributor not being able to be turned enough to advance the car to where it needed to be without the motor dying was diagnosed to a loss of grounding for the Petronix module. The ground is supposed to be picked up through the distributor. The FI distributor is several components and chevy distributors apparently do have problems at times with grounding. The fix was to run a separate ground wire from the Petronix base plate directly to the engine ground. Simple. In the process I also found a very clever and handy way to statically time a motor given that you know accurately what the advance curve is for your distributor. Don provides a very complete advance curve so that was easy. If anyones interested in using this method it only works with the PetonixI which is what I have. So the motor fired right up and advance beautifully to full advance. it was a good day.