Thread: New topend rebuild but can't get rid of the backfire

Tweet

As Lynn said the cap looks ok, but hair line cracks are hard to detect at times and is the rotor made of thin plastic? If I were going to change the dizzy I would pick the best one I could afford within my budget and IMHO stay away from anything from Accell. As I said earlier I would look toward Mallory or MSD as both make a quality street unit that won't break the bank.

I dont think its that interesting rerouting design. I have wired normally

Now that i think of it i believe it is made of a thin plastic. Whats the major brand rotors made out of?

Originally Posted by mikesaik

Now that i think of it i believe it is made of a thin plastic. Whats the major brand rotors made out of?

Used to be made of phoenlic, I'm not sure about what they are made of today, the thin plastic ones will heat up and warp over time and the blade will become loose in it's mount.

i did some searching today for a new distributor on summitracing.com and I did't realize how much of a selection there really is. I saved two that i posted on here to get some opinions on which would be better. Also for instance if i choose a Mallory Dist. should i also go with Mallory wires to match instead of mix and matching name brands?

http://www.summitracing.com/parts/ma...make/chevrolet

http://www.summitracing.com/parts/ms...make/chevrolet

Either one would be a good selection IMO and as far as wires go I'm running Taylor Spiral Core on the Vette and I've used them on everything I've had in the past few years. I think they are excellent wires for the price. I forgot, I'm running Moroso wires on the Mustang with an old Mallory dual point converted to Petronix.

Up on magnifying the pic--in the second cap photo the terminal on the right appears to be eroded away with quite a bit of splatter around it----------usually when something like this happens, it is a result of something external to the cap that causes it---look for crossed wires, a short or burntout section---------

Originally Posted by jerry clayton

Up on magnifying the pic--in the second cap photo the terminal on the right appears to be eroded away with quite a bit of splatter around it----------usually when something like this happens, it is a result of something external to the cap that causes it---look for crossed wires, a short or burntout section---------

Great eye Jerry. I'll take a close look at the cap and wires tomorrow and see what i find.

Originally Posted by jerry clayton

---------usually when something like this happens, it is a result of something external to the cap that causes it---look for crossed wires, a short or burntout section---------

See if that terminal corresponds to the wire that you said had short melted section that you had taped. Could be your problem....

Originally Posted by rspears

See if that terminal corresponds to the wire that you said had short melted section that you had taped. Could be your problem....

Later on today i'm going to trace that terminal and see if in fact that it the problem. If i was to just go with a gm replacement cap, i still need a new rotor though to replace the thin plastic one right?

Originally Posted by mikesaik

Later on today i'm going to trace that terminal and see if in fact that it the problem. If i was to just go with a gm replacement cap, i still need a new rotor though to replace the thin plastic one right?

Yes, it's very possible it's what caused the problem. O'reillys used to carry Standard brand, I'm not sure now, and their more expensive units weren't too bad.

That looks like a GM E/I if so get a GM cap and rotor. It won't be red, but Black. The cheaper caps cause all kinds of problems. If your plugs are black your to rich If white you could be lean you want like gray I'd guess as a color. you could have a sticky valve too. not closing as quick as it should. Me sitting here all I can do is guess. Good luck

Before you spend money on a new distributor, get a GM replacement cap. Much less expensive than a new distributor!

sometimes melted wires are because of lean conditions causing super heated exhaust headers/manifolds---
then plug misfires from ignition but unburnt mixture is lit off from exhaust on cam overlap causing backfire thru the intake-----this can contribute to supercharger space launch on 6:71 ---------

Originally Posted by jerry clayton

sometimes melted wires are because of lean conditions causing super heated exhaust headers/manifolds---
then plug misfires from ignition but unburnt mixture is lit off from exhaust on cam overlap causing backfire thru the intake-----this can contribute to supercharger space launch on 6:71 ---------

Say this is the reason its backfiring through the carb, why would small revs, idle and cruising all be fine? More gas at high rpm and such a weak spark can't ignite it?