A conundrum 3X8 Gods from the files of "easy project turns PITA": Installed the dual pickup Pertronix Ignitor II MR-183 electronic ignition on my '76 GT4's rear distributor. Lined up the +6-degree PM1-4mark on the flywheel and lined up the rotor with the red slot on the dizzy housing. Car will only start with the timing light hooked to cyl 1 showing like +40 degrees!!! When it starts it backfires through the exhaust from the rear bank, BUT ONLY AT IDLE. One would think it's actually retarded too much, because when it's running off idle it doesn't backfire and actually sounds okay. Any more advance, though (which requires the dizzy to be moved a tooth) and it won't start. My buddy and I cannot resolve why we can't find a place where it will start, but won't backfire at idle...and where the timing seems to make sense! What the heck are we doing wrong??? And how could it possibly be showing such high advance when the symptom would usually indicate too much retard causing backfiring through exhaust (rather than through carbs.) And these are good wires, new coils, good plugs, extenders. Thanks, Sam (who is going out of his skull trying to factor in all the crazy variables.)
And you have the 1-4 pick-up positioned so that the 1-4 firing event occurs when the rotor is lined up with the red slot? You didn't mention it, but did you also confirm you used the correct occurrence of PM1-4 (i.e., end of compression stroke, not end of exhaust stroke)?
put it on the timing marks using the cams and tdc via measuring, not using the flywheel marks. Then redo your Pertronix units. They are out of synch - either bc the flywheel is mismarked, or you used the wrong notation, or something slipped, or or or. Save yourself a million hours of guessing and just start over. It'll be a lot easier.
I'll recheck the 1/4 pickup position, but we had a ton of discussion about if the position was that crucial, since it simply charged the coil -- and the rotor hitting the contact was the firing event. (But we talked ourselves into a rabbit hole, so we could be very wrong.) As for the correct occurrence -- we had it backwards and it wouldn't start at all.
A long time ago when I converted my GT4 to electronic ignition, I had Crane Cams system and I had to do static timing like this. Use the front pulley, set the engine to whatever position you want the car to fire and run at idle. Turn the dizzy to its most retarded position possible. I Think this is as far counter clockwise as possible. Turn the key on to energize the ignition, Slowly turn the dizzy the other way until it discharges a spark. Stop, lock down the dizzy. Fire up your engine, check timing. The Crane system allows it to fire a discharge even when the engine is not running. So this was possible. I cannot tell you if Pertronix is the same. Good luck.
No, the rotor hitting the contact does not initiate the firing event (it's just that the rotor needs to be overlapping the contact with the firing event occurs). Using the red slot to mount the distributor to the engine only works if the pick-up is positioned such that the rotor is pointing at the red slot when the pick-up (or points or whatever) creates the firing event.
I just stripped the dizzy back down and built it up again. I assume that the reluctor can be mounted either of the two possible directions over the lobes, as there are four pickups evenly spaced? (I think I have the MR-183 imprint away from the red mark.) Still backfiring.
The reluctor mounting has no effect -- as you noted, it has 4-poles and the dist cam has four flats so the relationship between the rotor and the reluctor poles is always the same. The condition you need to achieve is that when the rotor is pointing at the red slot, one of the reluctor poles is in the location that will cause the 1-4 pick-up to fire (by moving the 1-4 pick-up to that location).
Phrase of the day: "Distributor rotor phasing" This is what my pro Ferrari-tech friend (who I hate to beat up for free advice!) has brought up. Has anyone had an issue with this on the 3X8s and the Pertronix system?
OK, too many opinions/ideas/suggestions... If you can wait until I get home this evening I will go out and take a look at my records and my gt4 which is running a Pertronix setup and runs like a train. Installation was very easy and everything went together just as the instructions say.
Is the the kit from pertronix's that comes as a bolt in. I had my dizzy done by Don King out in Ca. This was before pertronix's had a kit . I just sent him the dizzy and he sent it back ready for installation. Just reinstalled it and it started right up. Put the timing light on it and set the timing and never touched it for 10 years. Still in the car untouched as far as I know when I sole it 2 years ago.
Yes -- it is that bolt-in kit. Followed the directions in the kit and in the owners manual for timing.
YES !! The good news is that when you got the sensor plate properly positioned so it triggers the spark when the rotor is actually pointing at the correct HT lead, to my experience the Pertronix system is reliable and will give you no more worries. Additional note: maybe worth a check to see if the sensors/pickup's are mounted exactly 135degrees apart on the mounting plate. You will see that as different values hooking up the strobe light on 1-4, then compare to 5-8. I've seen sensor's on new units up to 3deg off. Maybe nitpicking -but why not have it spot on ? H
