Just put my '79 C30 service truck on the road recently. After a long 6 months of building it in the driveway, I was pretty darn excited to start working with it... until I discovered a really bad misfire/shudder over 2000RPM when under load. Which brings me here!
Everything has been serviced/gone through on the engine... plug wires, plugs, cap, rotor, distributor all rebuilt with new parts, carburetor rebuilt, vacuum lines all replaced, PCV valve replaced, etc.
-Has a Rochester Quadrajet carb
-Timing is currently set at 10deg (with dist vacuum like unplugged)
-AC R45TS plugs gapped at .045
-Dist power wire is good and getting full current from the fuse block
-Truck grounds are good and I added extra cables frame to engine
-While running, touched each plug boot with a screwdriver going to ground and nothing arced
-Previous owner installed an RV cam (whether it makes a difference...)
Took it on a service call this AM and had to turn back. At highway cursing speed (55-60) it was awful. Goosing it will cause the misfire will go away briefly, then come back once you let off. Climbing a big hill, mat the pedal and it goes away for about 20-30sec, then gets really really bad... stumbling all over, won't catch up with itself. The fuel pump did come to mind, but even if the truck is sitting there at an idle and you take off hard, it will still stumble once over 2000rpm or so. Any rpm under that and it's fine.
Any thoughts? Have some work scheduled in the next week+/- so would like to remedy this soon.
