On Tue, 18 Feb 97 Shane wrote:
snip
>Hypothesis 5): The popping on overrun to me means that unburnt fuel
> is leaving the cylinder and igniting on the hot exhaust
> manifold and/or pipe. Does this sound reasonable? I tried
> setting the mixture on the carbs leaner and richer trying to
> get rid of the popping, but no such luck. I guess I still
> have a leak sonewhere, perhaps in the idle circuit. 1974
> and later cars have a mechanism to shut down fuel flow when
> on overrun which is clearly not working in mine. Can anyone
> tell me what part of the carb I should look at next?
Shane,
Ever since my purchase of a '75 TR6 in August '93, I also experienced
the popping (backfiring) upon deceleration. I performed the complete
carb rebuild as you've done but to no avail. Then in the Winter of '95
edition of Moss Motoring, they had a tech article about backfiring.
One cause of backfiring is an overlean mixture and an overly lean
mixture can be caused if the engine is able to draw air from whence it's
not supposed to. I've since forgotten the author but his successful
solution was to take the input manifold off and have a machine shop mill
the head mounting surface flat. The shop, in his case, found the
surface to be warped a few mils. As the intake is aluminum an the
exhaust is cast iron, the author surmised that the manifold clamps and
previous removals, installations, and possibly overtorquing had caused
the intake to warp. In his case, a new gasket and he used new studs as
well, cured the problem.
After reading this article, I wasn't able to do much about resolving my
problem but I hardly drove my car too. However, I'm currently in middle
of an engine rebuild and I took my manifold to the shop for checking.
The shop pronounced that my manifold was warped too.
So, I can't give you confirmed recommendation but enough evidence to
satisfy me appeares to point to a similiar problem with your car.
Just my $.02 Good Luck!
Gary Klein
'75 TR6 Undergoing a Total Revamping!
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