backfires thru carb (truck sits alot) ***?
Ok, this is a 78' chevy c10 pickup with a 350 small block. its sat around alot the past 10 years i've had it. I start it up weekly though and drive small amounts around town sometimes. The engine is low mileage, but around 12 yrs old. I first suspected a timing problem, I put the light on it, and I put it @ whatever it said on the sticker under the hood. ( i believe it was 9 deg.) Anyway, it was ok and the timing is advancing correctly also. I ended up trying a different carb I borrowed from a buddy. After doing so I found major vacuum leaks at the carb gaskets. (it has a holley carb adapter). Ended up putting fresh gaskets, and getting that resolved and now there are no vac. leaks anywhere. I sprayed the whole engine down with carb cleaner to check around the intake manifold (where I could get the spray nozzle to anyway). The plugs look sooty when I pulled them last time. the cap & rotor have been replaced along with plugs and plug wires very recently. My vac. gauge inside the cab shows 15hg when its idling and the needle is pretty steady. It will rev up to about 4k rpms not under load before the misfiring starts. under load it starts to misfire around 3k or so depending on hills etc.. The engine has a mild cam (lost specs on it) and has a 700 r4 tranmission. is it possible the coil could be cutting out or bad rings, etc? I haven't done a compression test yet. I have a digital temp gun and I thought about taking individual cylinder temps with it to see if anything showed up. another thing the engine has short valve covers and i'm wondering if a rocker arm is smacking the vc even?
Anybody out there care to jump in and speak anything I appreciate any input!