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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: mjolinar on September 29, 2006, 01:06:00 am
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Hi all,
I am having trouble with my ignition timing I think, but it could be carburation. It backfires at high RPM when the secondarys open up and it kicks down for drive to L2.
Is the timing to retarded? That is my first guess. Second would be that the carb might be to lean in the primarys. I took it to someone to get it to pass emissions and he changed the timing to about 7 degrees btdc, and jetted it down....ALOT!
I have bumped the timing up to 10 degrees, but it still does it. Should I just time it for highest idle and back it off a few degrees.
Engine is a 350 rebuilt out of a 92' that has been heavily modified, but I have no clue what is inside or if the cam has been degreed.
Carburator is a Holley Truck Avenger 670.
Ignition is standard '78 HEI
Trans is TH350
Any clues as to what is causing this?
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Is your distributor vacuum advance? Check your base timing and your total advance at 3,000 RPM. Keep your total advance around 36° and see what happens.
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It was the mechanical advance...the counter weight stud had actually sheared off, and the weight was loose under the rotor, and had jammed into the mechanical advance holding it open. It had also frozen in place, so I put in a new distributor this weekend, and it seems to have cured most of my problems. I still have a vacuum leak that I am having no luck finding.
Edited by: mjolinar at: 10/4/06 10:37 pm
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Vacuum leak,get a can of WD-40 and with the engine running spray around the carb the intake manifold and anywhere you think could be a leak,if your RPM start to climb you found the leak.
Steve