hmmm?.. I'm not sure I've ever had such an issue like that and I always tune my ignition curves without them until I get it close.. and then I add the supplemental lead from the pot. and yep.. which is why I added that lttle bit to the end so you didn't think that I was simply trying to argue. Could be this.. could be that.. and it all needs to be checked before moving forward in the torubleshooting process. The first tests I would try is to just pull the hose off the manifold/carb and suck till your tongue hurts as you plug the hose with it(I know that sounds bad but we're all adults here.. I think) to make sure the diaphram holds vacuum. Then if it does?.. pull the hose off and plug the port to try and run without the vac pot and see what happens. Ideally we need a light on this motor over its rev range to see what's up though. That would forego all the old quick and dirty tricks straight away.
Ok been looking at it some today, I have it to where it's not hardly backfiring at all, it will do it once in a while, I double checked the timing and got it set to where it's better, I checked the vac. advance and it's functioning great also, I am kinda leaning towards ignition at this point and I'll tell ya why, I have a digital tach and at idle its fine I run at about 1000 RPMs and it's fairly steady, when I throttle up the tach will go up but flashes back to ZERO when the backfire happens, seems something ain't right for that to happen, may change out the coil first as I have an extra, I need new wires and those will also be replaced as I have no idea how old the ones I am using now are, I will do those things and see what happens from there, these are things I need or things I can do that are not going to cost me too much, and it's a fairly simple thing to check/replace, all of the suggestions are great and thanks to everyone for them, I am listening to ya!!! I am checking all things out, there is NO noise coming from the valvetrain at all, very quiet, no ticking, the carb as stated earlier has been gone through, junrai I am leaning towards you're thoughts on the coil.
what type of distributor are you running? ive seen the trigger wheels or the sensor mounting screws come loose and this causes what seems like an intermittent miss.
Vacuum advance has nothing to do with it. I had a blown vacuum advance about 25 years ago, and it simply caused a part-throttle hesitation. It really sounds to me like a carb issue. I know you said it was rebuilt, but that doesn't mean it was rebuilt correctly.
Yeah I hear ya but I think my guy's knew what they were doing on this one, seemed to know about Holley's pretty well, if all else fails I do have another carb.
No need to suck that hard If the diaphram is bad the breaker plate will not move. That one instance mine went bad was the one and only time it's happened to me and it had me stumped until I discovered it. I at first thought it was the carb acting up. No harm, no foul.
lol.. I pretty well figured that I left myself open for that one. To be clear though.. I've seen far more vacuum diaphrams with slow leaks than just outright cracked and blown diaphrams. Ideally a hand vac pump is all that needed.. but the old "vacuum suck and then plug the hose with the tongue trick" works too. If the thing slowly loses pressure and no longer sticks to the tongue?.. you have a slow leak. With no need for gauges or to even remove the cap to figure it out.
Ok put new coil on and new plug wires, still backfiring from the exhaust, I did find out it's only coming from the drivers side of the engine, will pull drivers side valve cover tomorrow and see what I can find, looking for really loose pushrods I guess, anything else I should look for?
bent push rod or sticking valve with the valve cover off and the coil disconnected you can turn the key over to see if each rocker lifts up all of the way if theres a problem where one isnt working completely it should be easily noticeable.
Shine a timing light on them. If they move different then you will see which one is moving wrong. If they look like they're sitting still then that's not the problem
'Took me about 5 years to figure out mine was bad. I never thought to check it, and I kept messing with carbs, manifolds, timing, and other stuff. Of course I was young back then...
