Charles D. Sorkin had this to say:
>>>I'm beginning to wonder if the manifold is cracked somewhere. When I back
>>>off the accelerator, say going down a hill, I get a decent crack or two from
>>>the exhaust.
>
>Max said:
>
>>This is normal, as far as I know, for twin SU MGs. At least mine has
>>always done it.
>
>Mine did it until I fixed a manifold/exhaust pipe leak. Doesn't it also
>happen when a gulp valve goes faulty? That valve tries to lean out the
>mixture when backing off of the throttle, but if it does not do so, and
>instead keeps the mix more rich and irregular than normal, won't that extra
>fuel ignite when it touches something hot, like the manifold?
>
Hmmm, my B doesn't have a gulp valve. Haven't noticed any leaks since I
replaced the manifold gasket last year for an intake leak (made no
difference to the backfire). The carb pistons, etc, may be a little worn,
though, but I have rebushed the shafts. Who knows?
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the red one with the silver bootlid.
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