This damn backfiring

How have you set the ignition timing? One cause of backfiring is leaks in the exhaust manifold eg. if the manifold is loose on the heads.

I beleive the ignition is set to the correct settings, i adjusted it so that at max advance the reading is 32 degrees BTDC.

On Tue, 6 Apr 2004 13:42:01 +0300, "Olli Lammi" ran around screaming and yelling:

I'm with Olli again....when ever you have afterfire in a vw, most of the time it is an exhaust leak...start there then work backwards....(forwards? LOL) JT

Look for exhaust leaks, the "burns in the pipe" requires oxygen to be present. It can only get there through a leaking pipe joint somewhere.

What kind of exhaust system is it?

What carb venturi size? Valve sizes?

Jan

The exhaust is a single glass pack, im pretty sure the valves are stock but as for the venturi im affraid i dont know. Thanks for your help though it has given me another place too look. Would this contribute the backfire between gears as well or is that another problem?

Same problem.

Jan

Thats kind of a relief!

I will investigate and let you know, thanks to all for your help.

If you have no luck there, I know a harley will perform similar errhant behavior on an intake leak as well.

-Matt '75 hd fx '78 vw bus

Ok so after spending a moring underneath the car and tightnening up all the exhaust nuts and bolts i took it for a drive. On the first part of the journey i drove to my destination bringing the engine to its normal running temp, switched off the engine and joy no bang! However when i returned home it done it just as loud as it did before.

Could the leak just as easily be on the intake to the heads? Or could the problem be down to jetting?

With the engine cold, start her up and move your hand underneath and around the exhaust. Listen and feel for a leak. You'll know if it's there. How do your spark plugs look? To lean a jet will cause similar symptoms, and eventually melt your pistons.

I'd be sure it wasn't an exhaust leak if I where you, and then using the propane or carb cleaner/wd-40/starter fluid trick, discount an intake leak. If that fails, richen up your jets. If THAT fails, pull out the stops and try voodoo things like higher octane gas or colder spark plugs :-P You sure it's a backfire, and not a knock?

-Matt

ok so im getting closer to the problem, after playing over the weekend i have reduced it dramatically. First was the mixture (still dont think it is

100% right but im working on it) then i adjusted the idle speed, it was running rather fast at idle about 1500rpm so i knocked it down to 1000 and the backfire is almost gone just a very slight fluff now!

I had the exact same symptoms as you, and after much kicking of myself, I found #3 & #4 plug wires were switched on the cap. The car had enough power to go and would go pretty well, but had the tell tale backfire.

Greg