1971 Volkswagen Beetle emissions

Hi there,

My guess is that the charcoal canister has never been changed in it's life. By passing it will no affect you problem, if anything a faulty canister will cause your engine to run a bit richer, back fire is usually a lean mixture or ignition timing problem. Is it back firing in the exhaust or carby? Exhaust i would be looking at a valve, or a timing issue. carby mixture to lean, cross firing leads, faulty distributor cap (carbon tracking) Vacuum leak, timing issue, faulty distributor. You would be best served to have the engine run on an oscilloscope and an exhaust gas analyzer, this will bee the best way to pick up many of these faults.

Mark (mhpautos)

you won't find btdc on the dizzy...
it will be on the crank pulley...
you'll have a notch for tdc, and on one side or the other i ferget which, there will be like an indentation, or dimple if you will. as long as it's the original pulley you should be in good shape there.
make sure the plug wires are in the proper order.
if you take off the dist. cap, on the rim of the dist. is a little notch. the rotor should be pointing at this notch at the same time the notch on the pulley is lined up with the split in the case...
for a better explanation...get the book.

john muir
how to keep your vw alive forever....

also, the valves must be properly adjusted.
too much advance will kill that motor in no time.
bypassing the canister won't affect anything.