Andrew Mace writes:
>Subject: TR250: intermittent missing @ mid-range
>The problem: once warm, there seems to be an intermittent sputtering/
>misfire at mid-range under slight load, i.e., 2000-3000 rpm and about
>1/4 to 1/3 throttle will produce some sputtering. I've been through a
>minor tuneup, cleaning this, resetting that, checking this and that. The
>diaphragms are intact, and oil level in the dashpots is appropriate.
Hmmm. mid-range, low load - have you checked the vacuum advance? It
should be providing extra advance in that situation. If it isn't, the engine
may be a bit more retarded than it wants. You could try adding in a few more
degrees of static advance (say 4?) and check to make sure no ping shows up.
My '70 TR6 has an unconnected advance (wrong carbs - '71), and runs much
better at around 16 degrees advance than the stock 10 or 12. Note that the
vacuum-advance distributors have less mechanical advance than the later
no-vacuum-advance distributers (by around 10+ degrees at high rpm). Perhaps
the advance is stuck, or the diaphragm is leaking. Easily checked - pull the
tube and blow into it to check for leaks (or suck, but you may get a mouthful
of fumes). My retard leaks.
>If it's indicative of anything, there is occasionally some very minor
>flooding (weeping is more like it) from the rear carb float bowl. (This
>one has been cleaned and checked -- figures! The front one has not been
>touched -- yet!)
Do you mean an exterior leak, or from the jet (float level too
high)? I'm guessing exterior, and that shouldn't be a problem. Could be
an improperly adjusted bypass (overrun) valve on a carb too, I suppose.
--
Randell Jesup, Scala US R&D, Ex-Commodore-Amiga Engineer class of '94
Randell.Jesup@scala.com
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