scorpion18z

I have just completed a "dizzy" rebuild to include pick-up coil, ICM, coil, rotor, and cap. I have been working with the timing set up with no total success. I can get initial timing set (10-12 degree before TDC), but as I throttle up (3000-3500 RPM) I get sputtering and backfire. She idles fine, but it does not want to run.

The initial symptoms was while cruising along at 75 mph just as smooth as a satin all of a sudden a few backfires and the car dies. I coasted to the side and had AAA pick her up and deliver her to my garage. Preliminary test showed no spark to the plugs, but 12v to the coil. This is why I rebuilt the dizzy and didn't look anywhere else. The spark returned with the rebuild, but I have the problem stated above.

Any suggestions from the forum would be appreciated. Note: The vacuum advance that I replaced was non-operational. But when I would connect the hose to the new one, it would run worse then if I left the hose off and plugged up. Maybe the HEI is computer controlled advanced. I am searching here.

DUB

So you are messing with advance weights and springs???? Is this area able to be rotated manually by hand and come back on its own?????

You did apply the special grease under the Ignition Control Module?????

IF you replaced it.....Did you replace the vacuum advance pod with the EXACT same type??? You are aware they can be different.

What year is your Corvette????

Guessing here...due to not knowing the year....And are you still using a the thermo-vacuum switch (TVS) to supply control vacuum to the distributor advance pod?????

Lastly...and I have written about this numerous times. If you are using a timing light to set your timing....are you 100% POSITIVE that the notch on the balancer is CORRECT. You are aware that the outer ring of the balancer can spin...thus throwing this notch off of its CORRECT location...and thus not allowing the timing to be correct...even though it will crank and run...it can be off. This may not have anything to do with your advance issue...but when I get problem ignition scenarios...I NEVER take anything for granted. You would be surprise don how many balancer I have found were off...quite a bit.

DUB

scorpion18z

I am not messing with the advance weights and springs.
Yes, they can be rotated by hand and come back on their own.
I did apply the special grease under the ICM.
I was not aware of the vacuum advance pods being different, so I do not know if I replaced the vacuum advance pod with the EXACT same type. I did replace with what was available for my vehicle.
My vehicle is a 1986 el Camino with a 307 c.i. I have had a RV cam upgrade and 600 cfm Edelbrock 4 bbl. These additions eliminated the computer controlled fuel/air mixture. Don't know how or if ignition timing is involved with these changes.
Don't know what a TVS is.

Thank you for your help. I am carting it off to a certified mechanic's garage tomorrow because I am stressed out trying to figure why, all of a sudden, I have this problem.