Lately my car has been backfiring on deceleration, it backfires when it gets revved high and then shifted, however, if i don't bring the revs up and shift at a low rpm it won't backfire, or at least im not hearing it. I went to adjust points, again, this has been probably the 3rd time in a month i have had to adjust them...when i went to adjust them and get it into the right dwell angle the screw that holds the points down stripped out the hole, went to retap the hole and that didn't help.

So my problem was the backfiring and not knowing what was causing that, now my problem is i had to buy a new distributor....

i don't think i will ever get my car painted at this rate, everytime things go right, something breaks a day later...

Anyone know why my car backfires on decel, it only backfires once, maybe twice...but never backfires on acceleration. I did a tune up a month ago on the ignition and set timing, etc....whats going on?

Should i just get an electronic ignition and be done with points, i seem to have to adjust them more often then they should be adjusted!!!!!!

you didn't indicate a flat spot on acceleration which could point to a lean misfire. sounds like it's getting a (rich) misfire at high r.p.m.'s, but it also could be loading up from your ignition issues... maybe point float. or an exhaust leak can cause your backfire on decel. maybe alittle of all. check for worn dist. shaft bushings. i'd definately go with an electronic ignition since you know there are issues with your points. they're cheap and easy to install (pertronics type anyway). sure is nice not having to deal with points... not one of man's better ideas. check for exhaust leaks too.

mike

Stock FI or Carbs?

I suspect a exhaust leak ...
Andy

I'll go with exhaust leak as well.

Why did you "have to buy a distributor"? And when you bought one, what did you buy? The Cap'n

The car is dual carbed, 40 idf, i replaced the exhuast gaskets a little over 3 months ago, maybe they are already bad. How does exhaust leaks lead to a backfire, i don't totally understand how that works, please explain.

The reason why i bought a new distributor is because ive been having problems with the one in the car, im pretty sure its the stock distributor, 37 years old, a new one can't hurt...009 is the new one ill be getting, wanted a mallory but definitely don't have the green for that....ive read the things about the 009, but my buddy has one is his 72 1.7L teener and he's never had a problem, so ill give it a shot

I'll vote exhaust leak also. Under deceleration, especially w/ carbs, there is a fuel rich environment in the muffler. An exhaust leak can let outside air, read oxygen, into the exhaust steam. Hot exhaust, fuel, oxygen = backfire.

How many exhaust gaskets are there?

One per port, unless I am not understanding the question.

I know removing the exhaust is something you shouldn't do that often, are there gaskets between the motor and exhaust port? I know of three flange gaskets, two i have replaced and the other is a triangular gasket, that could probably use replacing.

Ok, I think I might be able to help here but I am assuming a few things;
1. If your car is 70-74, it has the following for exhaust gaskets.
- 4 copper oblong ring gaskets that fit in the exhaust ports that the exhaust (heat exchanger) crushes slightly when tightened to the head.
- 2 two hole gaskets that go between the end of the heat exchanger and the muffler.

2. If your car is 75-76 is has the following;
- 4 copper oblong ring gaskets that fit in the exhaust ports that the exhaust (Y)pipe crushes slightly when tightened to the head.
- 2 triangular (3 bolt) gaskets that mount the stub (Y) pipe to the heat exchanger.
- 2 Triangular (3 bolt) gaskets that mount the heat exchanger to the muffler
- 2 Triangular (3 bolt) gaskets on either side of the catalytic converter of through pipe.

I hope that makes things clear. Yes, you should have a copper gasket in each exhaust port in the heads.

I have replaced the exhaust flange gaskets that i knew needed to be replaced, im a little leery to pull the entire exhaust system off the car to replace the exhaust port gaskets. However, today i got my car running again with the stock distributor and it was still backfiring on deceleration. I set my dwell and timed the motor, but the timing was off because dwell had changed and i couldn't seem to time the thing correctly without it dying. at one point, the car completely shut off because the screw that holds the points down slips and moves the points too far away thus making no spark. this is one reason why i bought electronic ignition.

Out of interest i decided to pull one of the spark plugs, and the one i pulled was black from carbon deposits. I think that my carbs are jetted wrong by a little bit making for really rich conditions in the cylinder, since the plugs are so carbon'd up the spark is weak and doesn't ignite all the fuel, that unburnt fuel plus oxygen from possible exhaust leaks makes its way into the exhaust and kaboom, backfiring....The only thing i don't understand is why in the world does it only backfire once , im assuming all my plugs look like the one i pulled so there would be unburnt fuel in the exhaust from all four cylinders, does it only backfire once because there isn't enough fuel to backfire again?

Am i on the right track on tracking down my backfiring problem? Im still waiting on my Pertronix Ignitor II and 009 distributor, hopefully i can get the motor timed and running right with the new dis. and ignition system. Then i can hopefully track down the backfire by re-jetting the carbeurators and getting my rich fuel conditions down to the right conditions.

the motor is a 1.7L dual carbed, any suggestions on where i should start with jetting?

Thanks everyone.

Make sure the intakes and carbs are tight also, 14 ft lbs I think. I had a decel backfire with a loose intake manifold.

Just tightened all the nuts down yesterday and new gaskets as well, gotta wait on my new dis and pertronix, before i can make anymore progress

fix all known issues first. it sounds like you have a few your sure of. what size carb, what jets? alot of carb guys here will know if you're close.

fix/check "maybe" things after you get the "for sure" stuff done 100%.



you know the definition for the word ass-u-me?

I was amazed, I assumed right , all the plugs were black, cylinder number 1 was the worst. I changed all the plugs, and got the new distributor in. After locating TDC on the compression cycle the car fired and then we timed it. runs great and no backfires. The old dizzy would not spin outside of the car smoothly at all, you could hear a grinding whenever you spun the thing, the new one spins nice and smooth. I would imagine that would play into my problems...New plugs definitely helped, car revs smooth right through the entire rpm range, it was never this smooth.

Pertronix is going to arrive on saturday, and ill install it on sunday before work.