backfiring through carb

Thanks for replies. I got some garage time ahead of me.

Yeah, I will check everything I possibly can before I pull the front end the motor apart again...

If you can't find a couple of wires in the wrong spot, then I think BigBird nailed it. I did this once when I was in to much of a hurry and the engine acted exactly like you discribe. Ended up that I had lined up the timing mark on the cam sprocket with one of the dimples on the crank sproket, not the timing mark. I was very lucky not to bend any valves and after I fixed the problem the engine worked perfectly.

Jack

Ok, so I finally got back out the garage checked the firing order and everything was as it should be.

I ended up taking the front end apart and made sure the timing marks were lined, they were. But I pulled the timing chain off and re installed it just to make sure.

I got it all back together and fired it up and it runs a lot better now...but there is still a couple issues.

The first is the timing mark is jumping and it seems rythmic. The timing will be there then every second or two is dissappears and the comes back....

I took it for a spin around the block and if I accelerate normal everything seems fine, but if I put my foot into it backfires.

Is this my timing chain is toast? or a vacuum leak? I did throw my vacuum gauge on it and at idle in gear the vacuum gauge showed 15 and it pretty steady..... I threw in the towel late last night and am going to step away from it for a day or two, but any ideas would be great! thanks - Brian

As you may notice, I am not much on posting, and I have not been here in a while, but I am sure some of the seasoned gear heads can answer the question as to the resutls of a cam without proper valve spring pressure?

Rob (First post!) :-)

Where are you setting the base timing at? (degrees)

trying to set it at 15 intitial, but it was hard with it bouncing. It was at the end of a long day, so i just as i started getting frustrated, i decided it was a good time stop for the night.

IF i had a vacuum leak, wouldn't my vacuum gauge been all over the place? it was steady at 15....

Steady 15 sounds good especially if a non stock cam.

What are the specs on the cam? If it's not bumpy 15in of vacuum is late ign. timing and it would do what you say it's doing. Whats you total timing at?

A slight vac leak will still let it stay steady(usually just a bit lower of a reading) as there's no intermittent interruption in the intake tract(which would make the vac gauge jump around) only that the mixture air/fuel ratio in the intake tract is now off enough to cause driveability issues. but if it got lean enough to cause a lean misfire then that would cause the gauge to dive for a split second as that cyl didn't do it's job.

Are you still using points? sounds like a bad distributor to me. Do you have the vacuum advance hooked up?? It should be on ported vacuum and not manifold. manifold will make it backfire when letting off as it pulls the timing a way up.

if your carb goes lean it will backfire on you, and since it doesn't pop when you ease into it, I would look there

Well I seem to have fixed the issue. It ran a lot better after I pulled everything off and reinstalled the timing chain, but was still backfiring under hard acceleration.

I made the mistake of setting the initial timing with the vacuum advance hooked up. I realized this and as soon as I unhooked it, my timing dropped from 15 to 5 initial... I reset the timing to 15 and took it for a ride (with the vacuum advance still unhooked and capped off) and it ran great. I still haven't hooked it back up yet.

Thanks all for the help in what to look for! As always, it is appreciated. - Brian

Good for you.
I am glad it wasn't something to painful$.
Just goes to show you we all forget things from time to time. Hook that advance back up and go have some fun.