Mark :
The black plugs seem to indicate the front carb is going rich for some
reason. To be sure, check for black smoke when it starts running
crappy.
Since you mentioned it being extra dirty, I'd guess there is crud
getting stuck in the float valve, holding it open temporarily and
allowing the carb to flood. With the engine warm, try pulling off the
fuel line where it enters the front carb, redirecting it into a suitable
container (like a 1qt canning jar) and briefly starting the engine (it
will run for a few seconds on the gas in the bowl). Repeat until no
crud shows up in the jar. (You might also decide to replace the rubber
line again at this point.) Then disassemble the float valve and flush
between the valve and the inlet with carb cleaner.
Another possibility is a partially saturated float, that no longer holds
back the fuel pressure when it gets warm. I don't know of any good
diagnostic, except to substitute a 'known good' float (like the one from
the rear carb). Sometimes, you can cure this problem by coating the
float with "hot fuel proof dope", available at a hobby shop that caters
to model airplanes.
I've never tried Grose jets, but I've heard from several people that
reported problems somewhat similar to yours 'went away' after they
switched back to the stock float valves.
Randall
59 TR3A daily driver
"Evans, Mark" wrote:
>
> Oh great knowledge base...
>
> I'm having what I suspect are carburetor problems and wanted to bounce the
> symptoms off the list to see if my reasoning is correct and to hopefully get
> some ideas about what I may be missing. Sorry for the length of this post.
>
> I've static timed, set the point gap, replaced plugs , distributor, rotor,
>plug
> wires, low tension lead and added a Lucas Sport coil. Have disassembled and
> cleaned the carbs (SU HS6) - pretty routine tune-up stuff.
>
> None of this resolved the problem. The car responds well to tuning while at
>idle
> before and after the work described above. I drive down the road about 2 miles
> winding it through the gears and having fun. It runs absolutely fantastic then
> starts missing/sputtering until I have no power and must turn around and come
> home. Inspection of the spark plugs reveals cylinders 1 and 2 are fuel fouled
> (dry black) while 3 and 4 are medium tan. I been through five iterations of
>this
> - cleaning the plugs after each run and tuning again.
>
> I have adjusted the mixture many times and get the proper short rise in idle
> speed and settling down on both carbs when lifting the piston. I suspect the
> front carb float misbehaving but can't seem to verify this. I use the carb
> cleaner trick on the throttle shafts and can't conclusively determine if there
> is a vacuum leak though by hand the shafts can be wiggled slightly. Both front
> and rear carbs have a similar slight amount of play in the throttle shafts.
>
> This all occurred after the car sat for 9 months of shipwrights disease. There
> was only 1/2 gallon of gas in it and it was not treated/stabilized so I
> suspected I'd gummed the works. This gas should have been worked out by now
>and
> it has fresh premium in it. All fuel lines have been cleaned or replaced and a
> new fuel filter installed. When I cleaned the carbs they were quite dirty -
> especially the front float bowl. It ran fine 9 months ago. It has Grose jets
>for
> float valves.
>
> Any ideas?
>
> Thanks,
> Mark A. Evans
> 1966 TR4A IRS CTC63970 LO
> markaevans@mindspring.com
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