Peter,
Carb backfires are almost always due to a lean mixture. I'd start by checking
the plugs. If you're sure you have the idle mixture set correctly you may have
a vacuum leak that happens under load (can't think of anything that would cause
that, but I suppose it's possible). Like another Lister said, check your
dashpot
oil ... a thicker oil might help (20W is recommended). You might also have a
sticking vacuum piston ... make sure it's clean with no burrs (but don't remove
any metal, it's a precise machine fit).
BTW, how do you know it's the rear carb? They sound the same to me ;)
bs
********************************************
Bob Spidell San Jose, CA bspidell@comcast.net
'67 Austin-Healey 3000 '56 Austin-Healey 100M
********************************************
> For a while now my BN1 - based car has been spitting back through the rear
> carb. This happens for rather longer than you would expect on a cold engine -
> it usually only needs choke to start, & seems to run OK at all speeds, but
> there is the occasional spit-back, through the rear carb only, until the motor
> is really up to temperature. This seems to be mostly on a light throttle. The
> carbs are pretty well set up I think (H6s) using carb balancer & lift pins.
> The plugs look OK and are consistent across the cylinders. The carb spindles
> are getting a bit worn but the front is worse than the rear in this respect.
> Timing is set with a strobe but I'm not 100% certain of the total advance.
>
> Any ideas?
>
> Peter Linn
> Brisbane Oz
> BN1 Ward Special coupe
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