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Discussion Starter · #1 ·
Hi guys it's been a while since i posted but I've got a problem that just wont seem to go away. Got a 305 with a few mild mods (headers, carb, intake ignition) that has been running weird lately. It pops from the exhaust and idles roughly. Car is a 3rd gen Monte Carlo with an hei dizzy using a pertronix flame thrower coil.

The popping is not very loud, like a bang from improperly wired plugs but usually very quiet, the strange part is it comes and goes all by itself. I found the distributor rotor was loose so I tightened it back down, rough running ceased for a couple days and the car ran normal. Tonight however it began again, I've found the rotor to be slightly loose and re tightened it. But the problem still persists. :confused:

Help would be much appreciated.

Things I've tried are:

Verified the timing
Tuned idles mixtures
Checked for vacuum leaks
Verified firing order
Checked the distributor cap and rotor for anything strange.
Tested the coil (tested fine)
 

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An hei with pertonix coil, eh!
How does that work.
Never saw one like that.
And how did you tighten the coil?

Pics would help.

Plus check your rockers for proper movement. Could be a flattened cam.
 

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Discussion Starter · #3 ·
An hei with pertonix coil, eh!
How does that work.
Never saw one like that.
And how did you tighten the coil?

Pics would help.

Plus check your rockers for proper movement. Could be a flattened cam.
Looks just the one in this picture, fits into the top of the dizzy like any other hei.

http://image.superchevy.com/f/8945763+w640+h426+q80+re0+cr1+ar0+st0/p137772_image_large.jpg

Wouldn't a bad cam cause the motor to run poorly all the time?? I guess it doesn't hurt to look, I'll pull the valve covers and have a look.
 

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Discussion Starter · #7 ·
Did you limit the vac advance too?
Are you plugged into ported or manifold vac for the pot?
I rebuilt the distributor last year and replaced everything on top with Pertronix parts, including the vacuum advance canister. Never tried doing anything with it before, as the car ran very well after installation was complete.


I have the vac advance hooked into ported vacuum.
 

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I thought you said you tightened the coil, but it was the rotor instead.
How does the rotor get loose?
Is it clean inside the cap?
Maybe you’ve got a little spark scatter inside.
Have you tried running it without vac advance?
 

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Discussion Starter · #9 ·
I thought you said you tightened the coil, but it was the rotor instead.
How does the rotor get loose?
Is it clean inside the cap?
Maybe you’ve got a little spark scatter inside.
Have you tried running it without vac advance?
I tested the resistance of the coil with an ohm meter, looking to see if was the problem. It ended up testing just fine.


The rotor was part of the Pertronix hei tune up kit I bought, I removed it last September to replace the 4 pin ignition module that ended up blowing after 2 months. When re installing the rotor I must not have tightened it right.


Inside the cap appears to be fairly clean, I didn't see any evidence of spark scatter myself, though I suppose it is possible.


I've noticed my fuel mileage has dropped to almost half of what it used to be. I'm suspecting the module might be bad again or possibly the magnetic pickup.
 

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Might not hurt to swap in another hei if you got one.
I always had a spare kicking around.

On another thought, what carb?
 

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Discussion Starter · #12 ·
small update.

Had some time before work today to pop off the valve covers and watch the rockers with the motor running, all valves appear to be opening and closing normally. No loose rockers or anything of the sort. Won't have time until the weekend to start looking more into the dizzy itself. For those more familiar with hei distributors, anything else to check besides coil, magnetic pickup and module as far as getting good spark goes??
 

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Your module can be tested at any parts store but my hunch is its not your 'distributor itself.' No ones mentioned it but you say you have this popping problem, i was just thinking have you checked you muffler to exhaust manifold connection? Also thought about a bad exhaust manifold gasket. both will give you the popping sound in addition to the other things you mentioned but you've said you've checked those other things so reckon they can be ruled out..
 

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Discussion Starter · #14 ·
Your module can be tested at any parts store but my hunch is its not your 'distributor itself.' No ones mentioned it but you say you have this popping problem, i was just thinking have you checked you muffler to exhaust manifold connection? Also thought about a bad exhaust manifold gasket. both will give you the popping sound in addition to the other things you mentioned but you've said you've checked those other things so reckon they can be ruled out..
I suppose it's possible, I've heard of loose exhaust connections letting fresh air in that can cause popping. Would fresh air in the exhaust make the engine stumble too?
 

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Discussion Starter · #15 ·
More weirdness happening, now the idle seems to be adjusting itself if that makes any sense. I have the car set to idle at 800 rpm in park - about 550-600 rpm in gear. When I started it up after work to drive home, I found it idling at 500 rpm in park. A quick adjustment of the idle screw on the carb took the idle back to 800. However after arriving home, I shifted from drive to park I found the car suddenly idling at nearly 1200 rpm. ????

What gives? Only two ways I know of to adjust the idle like that are the screw on the carb and moving the dizzy to adjust the timing. I thought maybe the dizzy was loose so I tried tightening it back down, but couldn't get the bolt holding it in place to budge. Could the shaft be worn causing the idle to wander?
 

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The weights in the hei can change your idle like that if they’re sticking.
Or a light a set of springs won’t pull them back all the way.
 

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Checked your plugs? Fouled plugs will give those symptoms...

Russ
 

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Discussion Starter · #18 ·
The weights in the hei can change your idle like that if they’re sticking.
Or a light a set of springs won’t pull them back all the way.
I do have lighter springs in the dizzy to make it advance earlier, i'll try a little wd40 on the weights to see if that helps.


Checked your plugs? Fouled plugs will give those symptoms...

Russ
I just changed the plugs only a couple of weeks ago, with a fresh set of NGK platinum tips. I'll pull them this weekend and have a look.
 

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Huge Guns N Roses Fan
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another caveat to that are the springs themselves. Examine them to make sure they are not bent/stretched..
 

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I suppose it's possible, I've heard of loose exhaust connections letting fresh air in that can cause popping. Would fresh air in the exhaust make the engine stumble too?
muffler to exhaust manifold/header is a long shot, but thought i'd mention it considering all the other ideas that'd been thrown your way. Did not know you had a stumble problem...that being said, a loose muffler connection to flange should not give you a stumble in motor problem. sorry just now responding, been off for a few days.
 
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