Jim:
My '67 B, which has SU HS6 carbs on an after-market manifold, had the
same problem at a couple of hundred RPM lower. It felt to me much the
same as it did at any other steady-state speed when the engine was
very cold and running with the choke off, so I attributed it to an overly
lean mixture at that particular RPM, even when the engine was fully
warmed up. I graphed all the diameter measurements listed in the
Haynes SU Carb Manual for the needles that were in the carbs as the
base line, then searched for needles with a similar profile at the
top and bottom but richer in the middle. It was a very quick & dirty
method, but the new needles eliminated my stutter. A more accurate
method would be to rent a little time on a dyno, pop a sniffer up the
tail pipe and swap a couple of dozen needles in and out until you
found the proper profile to maintain the correct air/fuel ratio
throughout the rev range. My method was much cheaper, though probably
not as effective.
Regards,
Jerry Causey
> While taking my standard lunch-hour country drive, I was reminded
> again of the one operational glitch in my 72 MGB engine . . . At about
> 3200 RPM, or 60 mph in 4th, the engine misses/flutters/stumbles a
> little. The kicker is, the car has a '67 manifold with '72 carbs.
|