> After a lot of help from all of you, my 80B passed emissions. Problem now
> is backfiring! Car has weber downdraft, new plugs, points, runs fine in
> neutral. Under load it's a real eye-opener. Timing was set correctly. Where
> should I start? Too rich, too lean?
David,
If it backfires when you take your foot off the gas and put the clutch in
to shift, the most likely cause is a faulty gulp valve. Under load, the
air pump is supposed to pump air into the exhaust manifold (via the ports in the
cylinder head. When you take your foot off the gas, the gulp valve is supposed
to divert that air pressure into the intake manifold. This will have two
effects.
First is leans out the mixture and second it cuts down on the amount of air
going into your exhaust manifold. As I understand it, it is this excess air
in the exhaust manifold which causes the backfire when shifting syndrome
on MGBs.
My solution to the problem was to buy the anti-backfire kit from VB. Installed
as per their instructions, it totally eliminated the problem.
Peter Schauss
ps4330@okc01.rb.jccbi.gov
schauss@worldnet.att.net
1963 Austin-Healey 3000 Mk II
1980 MGB
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