QuestionWhat would Cause my 1984 Chevy P30 Motorhome 350 V8 to spit, sputter %26 slightly backfire %26 pop ?
Answer It could be that the carburetor needs rebuilding, it's pretty old. Quadrajets had a peculiar throttle-plate design which frequently developed leaks in the bottom, allowing the vacuum to pull excess fuel into the manifold. When a rebuild kit is used they supply a special plastic foam plug to cover the area that leaks. Most good mechanics will belt-and-suspender this area by covering the leak with a layer of clear epoxy. Only epoxy will work here, not silicone or polyester resin.
It could also be caused by the evaporative emission control, commonly referred to as the charcoal canister. If they become soaked with liquid gasoline the charcoal breaks up and ends up in the float bowl.
A very common cause of these symptoms is a worn timing chain. Once the chain becomes stretched it cannot accurately control the cam or ignition timing. The best way to check this is to take the distributor cap off and rotate the engine forward and backward by hand. If the ignition rotor does not promptly follow the motion of the engine but, instead, moves only after an appreciable amount of rotation of the crankshaft, then the chain is loose and must be replaced.
But, and this is important, you must not undertake any diagnosis until you have given the engine a complete ignition tune-up. This means new wires, plugs, cap, module, pickup, and rotor (I would recommend a new coil, as well). GM HEI distributors also have another problem with the distributor. The centrifugal advance is built into the top of the shaft (under the rotor). The pins on which the weights turn become worn cause the advance to bounce around erratically. This is a very common problem with these distributors and most have already had GM's fix for it installed. Motorhomes tend to be low-mileage vehicles, however, and yours may still have the original advance weights and pivots in place.
