Robert,
Quick drainage of oil, from the carb dampers, point toward a worn O-ring
on the mixure aduster, down in the carb piston. Lack of oil in the damper
can cause acceleration problems on ZS carbs. The oil offers resistance to
piston rise during acceleration, temporarily increasing fuel ratio
portion of the A/F stream.
With your engine mods, you may also need a little thinner taper on the
needle height that corresponds to the 1500 rpm range. Once you vary from
stock, you may need an overall slightly thinner needle profile to keep up
with engine demands.
Best way to determine if this is the problem is with a CO meter, watching
the A/F ratios and CO readings as you go up through the rpm range. You
may be suprised to find at 1500 rpm or maybe 3500 rpm, an A/F ration of
only 18 or 19 to 1.
With modern fuels, and no cat converter, a little black soot in the tail
pipe is fairly normal. If you can see black smoke in your rear view
mirror, that's not normal.
By the way, how are you adjusting the carbs? With the tool in the damper
chamber, or the fine CO adjustment on the side of the carb?
Charlie B.
>
> I have a problem with rough running of my TR6, and I am hoping the wisdom
> of the list may be able to help. A little background I have a 74 with a
> little bit of a built engine, shaved head, mild cam, stock carbs, electronic
> ignition (Piranha). The car runs great with fresh plugs but after 200-300
> miles it developes a miss at around 1500 rpm. It pulls strong after that all
> the way to redline. When I replace the plugs they look fine. Adjusting the
> carbs seems to make no difference. I do seem to use quite a bit of oil in
> the carbs need to be filled about every 50 to 100 miles. Also there is
> usually a fair amount of black soot around the tailpipes which leads me to
> belive a rich mixture, but again the plugs look ok when I replace them. The
> car does not burn any oil, just drips it.
> Thanks in advance for any suggestions.
> Robert Rudolphi 74 TR6
> Baltimore Md
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