Another exhaust backfire question

[Fred K-OR]

I know, there are a lot of posts on exhaust backfire problems which I checked. But I could not find one like mine.


First of all, a few weeks ago, I drove my huckster a number of miles with various driving conditions. Everything ran great-no backfire problems and no other problems.


Today, I take the rig out, and I shift down to second for a stop sign, and BANG. It almost blast me out of my seat! And the engine dies at the stop sign-have not had that happen before either. I made no changes to any settings before leaving, such as GAV, etc..


I put in some MMO in the gas for a hoped for quick fix, took it out again and still had same problems.


Any ideas???


I found comments on the site such as: Point gap closing up, condenser, vacuum leak, etc. which sound like these may be a problem. Will have to do some checking in the A.M. but if anyone has a good idea, please through it out!

 

[Jacksonlll]

You probably have an intermittent break, or short to ground, in the circuit from the passenger side of the coil, up to the ign switch, and down to the dist, and up to the movable point arm.
Loose connection at ignition switch. Common prob.
Little black wire in dist.
Armored cable screwed too far into dist.
If that circuit is broken, and then connected, it can cause a backfire.
It’s like turning the key off, then on. POW !!!
Good luck.

 

[Fred K-OR]

Eliminated a coupe of possibilities. Checked intake with starting fluid-no engine speed up. Checked point gap-looks good. Will check some other possibilities next.

When the rig runs at just up from an idle, it seems like a cylinder seems to miss fire every now and then. Also will not idle even with adjustments of carb.

Could this be a sticky valve(s)?

 

[steve s]

You probably have an intermittent break, or short to ground, in the circuit from the passenger side of the coil, up to the ign switch, and down to the dist, and up to the movable point arm.
Loose connection at ignition switch. Common prob.
Little black wire in dist.
Armored cable screwed too far into dist.
If that circuit is broken, and then connected, it can cause a backfire.
It’s like turning the key off, then on. POW !!!
Good luck.

Read this again.
It's probably an intermittant bad electrical connection, either open or shorting to ground.
jiggle every connection while its running (not high-voltage ones!). Install jumper cables around those that might be failing internally and out of sight (like ignition switch) and ammeter. Try a new condensor.

OR, if it runs at high speed but not at idle, idle jet is plugged. THis can be cleared by racing the engine manually with throttle, suddenly releasing throttle while simultaniously briefly clap palm of hand over carb intake. Engine vacuum will suck blockage on through. If this doesn't' work, quit messing with carb and fuel supply.

 

[Fred K-OR]

Just thought I would get back on again to let you all know how things are working.


Things I did based on your comments.
1. I did check out all the electrical connections around the dash and where the wires come out to the distributor. Then I started it up to see if the messing around with the wires would improve things. Still the same problems!
2. When I got back from a test run mentioned above, I noticed that the carb was leaking a lot of gas which it had not done before and had been in use for a number of miles.
3. So I changed the carb to another that I had rebuilt earlier. Started it up, and it started like it always use to, with one touch of the starter and a little choke. Went for a drive for 5 miles or so with various situations and every thing worked like it use to!!!!


So don't know for sure what it was but it looks like something may have been in the carb to cause the problems.
I took the carb apart(that I just took off) and did not find anything wrong. Float was where it should be, did not find a bunch of crud in it. The only thing I found when I took it off was that the gasket between the carb and intake manifold had some wet stuff on top, likely gas and the bolts holding it on were not real tight. So maybe the problem was a bad gasket that caused a vacuum leak at this spot.


Anyway rig is running great again thanks to you all giving me some ideas.

 

[Synchro909]

Thanks fro getting back. Many do not and we are all left wondering whether it was our suggestion or someone else's that did the trick, assuming it has been fixed at all.

 

[steve s]

Read this again.
It's probably an intermittant bad electrical connection, either open or shorting to ground.
jiggle every connection while its running (not high-voltage ones!). Install jumper cables around those that might be failing internally and out of sight (like ignition switch) and ammeter. Try a new condensor.

OR, if it runs at high speed but not at idle, idle jet is plugged. THis can be cleared by racing the engine manually with throttle, suddenly releasing throttle while simultaniously briefly clap palm of hand over carb intake. Engine vacuum will suck blockage on through. If this doesn't' work, quit messing with carb and fuel supply.

What do I know?!