I just got through fixing a friend's Chevey PU -'85 4X4 350.
It had a couple rocker studs pull out and bend push rods.
After getting it running, it has a very fast, light backfire through the carb, starting at about 2500 RPM.
The engine has only 6K on it since a complete rebuild, balance, line bore, etc.
The carb is an Eddlebrock replacement Quadrajet on an Eddlebrock performer manifold.
The valve springs are all new.
When I had it apart, I noticed the dielectric grease under the module had turned to white dust. I cleaned the module and plate and put in new grease.
No mechanical noises, starts and idles great.
No real miss, just a rapid pop, like the throttle blades are fluttering - gets worse as RPMs climb.
Where should I look?
Carb power piston?
Ignition module or pick-up?
EGR?
Something more expensive?

 

Sound like the cam is going flat.

How tight did you set the valves??

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

GO #3

 

Set all to 1/2 turn past 0 lash.
Set cold - intake open, then closed - then checked running.
Cam break-in 20 minutes >2,000, varying rpm.
No single cylinder miss, just rapid pop.

 

if you pulled out two studs and bent pushrods, you definitely have a problem. elementary, but make sure you have hydraulic lifters and not solids. I have seen that before. also, make sure you are not coil binding the valvesprings. Kyle

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Kyle Osterholt
Okarche, Oklahoma
ASE Master Certified
86 T/A 383 TPI
89 TTA #1002 T-top/Leather
89 TTA #1358 Hardtop/Leather
80 T/A Pace Car
73 Opel GT