leroycjr

I hadn't done a tune up for a loooong time so I took this month doing all fixins (oil change, coolent flush, plugs, cap, rotor). Initially once all that was completed I was getting a misfire upon lower rpms during acceleration. Next I said hell with it and put in a new module on distributor. That stopped the lower rpm misfire but now while at higher speeds on acceleration I get the misfire. Today I got my 10mm wire set and figured that was the last piece of the puzzle. One for one I replaced each wire and then start it up fine.

Was running as normal and then I rev'd the gas lightly to idle it down a bit and POP & flame came from the carb and the engine immediately went to high rpms and stayed there. I turned it off, checked the wires and tried to restart. Goes right into very high rpms.

No idea what to do next. Only thing I though I'd try is retiming the engine since its technically been a few years since a full tune up but not sure that is needed.

Thoughts? The misfires and todays recent carb pop is concerning me as it's never happen in the 10 years I've had it post rebuild.

Any help appreciated

oldcutlass

Before chasing the misfire, check your carb linkage to make sure it's coming back to idle all the way.

olds 307 and 403

Are they ready made wires or did you crimp them? I alway check resistance. Make sure everything is clipped on tight. Check the voltage to the HEI as well. What brand plugs and gap? You may have a vacuum leak or you are running lean.

leroycjr

1. I'll definitely check the linkage
2. Ready made wires, Delco .30 gap plugs

The carb does look like it's got a nice amount of carbon on the float.​​

Cutlass Fan

"The carb does look like it's got a nice amount of carbon on the float"
Not sure what you mean by this as there is no way carbon can get inside the float bowl. Also if you have HEI ignition shouldn't your plugs be gapped more than .030?

leroycjr

I was reading here that with HEI you didn't have to run wide gapped plugs so .30 was my go to. Im running a Flame Thrower HEI distributor so I'm open to suggestions if I should bump them out to .35 or .40

olds 307 and 403

I usually run .045", it might help. I have seen what worn spark plugs with a .080" factory specified gap do, they don't start! Take an ohm meter to the wires, make sure they are right. I had ignition and carb issues on my 70S. The well worn motor started knocking. Double check everything and go through the carb. My ignition issues were proper voltage supply and the pick up lost it's air gap in the Mallory Breakerless distributor. My carb was working fine, took it off and put it back on, starting flooding at half throttle and above. I fixed the voltage supply issue, swapped to one of my HEI's and rebuilt the carb. It is a proper starting point for the new motor.

oddball

HEI *can* support wider gap (up to 45), but that won't help this problem.

The high rev is definitely a carb problem. Possibly linkage, possibly internal leak from old gaskets.

The backfire is probably also a carb problem. Lean spikes cause backfire. Also sounds like the carb might be leaking gas.

Do a basic clean and rebuild of the carb and check your ignition timing.

leroycjr

Didn't want to leave this thread in limbo and appreciate all the help. I finally got around to regappping all the plugs .045 and checking all the wires. Car starts right up and idles fine now guess that helped. I took it for a spin and it accelerated well at consistent speeds.

The issue now is...if I'm driving say 30mph and start accelerating to highers speeds, the engine/speed picks up, mph rise and then all of a sudden I hear like a loud "psssss" like air pressure quicky escaped from somewhere. The car buckles, the acceleration of course stops but then the car picks up again but I can pick up where I left off on the acceleration but then again "psssss".

​​​It literally happen whens I'm trying to open it up or do any passing acceleration. I'm stumped now its. Bad gasket somewhere? Vacuum issue some where? This has never happened before this tune up and new parts.

New parts:Pentronix Flamethrower cap, rotor, moduleAftermarket 10.5mm wires (pre made)
AC Delco 45 plugs

Cutlass Fan

Have you checked your carb? How long since it was rebuilt? I just rebuilt mine and adjusted the floats and secondary air valve. Solved the bog my car had.