Distributor curving.

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tekslk

tekslk

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Did my friends 340 tonight we have 37 total with 16 initial. This really woke his motor up, when he left of the gas on test drive it backfires, could we have a loose wire to dizzy or possibly bad rotor witch didnt fit quite right when it can off and went back on? no problems before we started, just lazy.
 
Which distributor? MP?

Check the air gap on reluctor/pickup.

Check all the wiring, firing order, the normal stuff. Look over the rotor, make sure center tang isn't cracked/broken. Cap got any cracks.

If the only thing you did was remove and mess with the distributor, I'd guess the issue is isolated there.

Is the accelerator pump adjusted properly and providing enough squirt when it's needed?
 
I would put a new rotor in and while I was at it,I would make sure your weights are returning. sounds like they are hung up or flopping around.
 
accelerator pump good, plastic slot inside rotor was half missing, I didnt check the gap on recluctor rushed a little, cap was new 2 months ago its probably a easy fix just have to narrow it down. it is a stock reman mopar dizzy I curved it and just threw it together so he could get it home. He said it ran great just back fires when he leaves off gas.
Thanks crackedback,and everyone else. When I put new springs on weights seamed good.
 
Might just be to much timing.
Bring it back a couple of degrees and see how it acts.
 
After you changed timing, did you readjust the carb, both idle speed and mixture screws? Get those set to the idle speed you want then the best leanest idle and see where you end up.

Is it backfiring when he steps on the gas? Could just be very lean at idle and then worse at tip in if so.
 
Backfires when you let off gas. carb readjusted, runs great just the backfire when you leave off gas.
 
We have no more timing than before we curved it, just a smoother transition. yes vacume was pluged. I can take some off vacume do you go counter clockwise to do this? Im thinking more toward relucter gap or lose wire since everything was perfect before. will also try a diffrent rotor.
 
Backfire through exhaust is late ignition timing. Make sure you put the reluctor back on correctly- assuming it's electronic ignition. If points, check your dwell. Make sure all your electrical connections & primary ignition wires are good too. I'm also assuming that you didn't change anything else while you were in there? No changes to carb etc? Plug the vacuum advance back in too & see if that changes anything.
 
Yeah, knowing if it's backfiring out the carb or exhaust is important. I assumed it was out the carb on tip in.
 
Exshaust only when you let off gas. I will check relucter tonight i have a feeling that might be it since i forgot to ck gap last night.
 
Gap on reluctor was at 4 thousands, regaped it to 8 idles good did not road check yet roads too wet but I think we have it.
 
I doubt a problem with too little reluctor gap, as long as the magnet doesn't hit the teeth.

Popping thru the exhaust when decelerating is common. Many motorcycle carbs have a bolt on part (forgot name) that adds fuel under high manifold vacuum (decel) so it doesn't pop, which suggests it is from "too lean" misfire, putting unburned mixture into the exhaust. Many remove them, to save fuel or because they like that popping sound. I suspect if you don't totally let off the throttle in a low gear, it won't happen.
 
Its a.loud bang pop bit will hopefully be.able to drive.ot tonight.
 
Road check bad. Un plugged vacume advance it works great, would it be a bad advance or something else? Dont tell me to tell him to run without he wont want that.
 
What do you have the vacuum advance plugged into? Manifold or ported vacuum?

Also, my suggestion about the reluctor wasn't just about gap, but if it's upside down or not. Many of the reluctors are not keyed the same position if they are upside down & the teeth on the reluctor would be in different positions relative to the distributor shaft & that would throw your timing off. Just trying to clarify my earlier comment. I hope I made sense.
 
Vacume plugged into the right upper forward side of carb, holley 770, reclucter is keyed, popping went away, when we on hooked vacume advance up is when it pops.
 
do you have a header/exhaust leak. Oxygen & unburnt fuel will cause this problem on deceleration. Fix the exhaust, fix the problem...JMO
 
No leaks only doing it with vacume hooked up, timing is 16 initial 35 total with advance pluged. Im sorry the poping starts with the vacume advance hooked up.
 
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