What weight oil are you running in the carbs? Given that this happens on
acceleration, I can think of at least 3 possibilities. First is that you're
running a heavy weight oil in the carb dash pots. This means that upon
acceleration, the mixture goes rich too much. If you then hold the rpm
steady, though, the mixture should stabilize and the engine shouold smooth
out. Another possibility is that you're running the correct weight oil, but
the front carb is just set too rich, and the normal enrichment that occurs
at acceleration is enough to make the fuel/air charge uncombustible
momentarily. Again, this should go away if you maintain steady pressure on
the accelerator pedal. A third set of possibilities is that there is a
problem with the piston or needle (bent, malformed, whatever) such that the
piston no longer rises and falls smoothly in the carb body. This could
cause the mixture to vary between rich and lean, I think.
To check for a too-rich carb setting, bring the engine to operating temp.
Remove the air filters. Use a narrow screwdriver to raise the carb piston
about a 1/16". If the engine rpm picks up and stays up, the mixture is too
rich. Turn the mixture nut (jet nut; the big one at the bottom of the carb)
clockwise as seen from below: you are screwing the jet upwards into the
carb. Turn one flat of the hexogon at a time. Re-check. If the rpm speeds
up then drops back to where is was originally, the mixture is just right.
If the rpm drops when you raise the piston, the mixture is lean and the jet
nut should be turned counterclockwise to lower the jet. Putting the
airfilters back on will enrichen the mixture a little less than one flat's
worth.
YMMV,
Jeff
At 7:54 PM -0400 7/23/99, chuck wrote:
> Still running lousy. I cleaned and gapped the plugs,
> checked the point gap, set the dizzy to the fastest
> idle around 1200 rpm.
>
> 1. starts right up fine.
> 2. seems to idle pretty well around 900-1000.
> 3. runs just great in reverse down the driveway.
> 4. starts fine in 1st until the revs pick up.
> 5. then runs rough, falters, stumbles as I accelerate,
> but with smooth spots here and there. Like an intermittent
> short or something.
> 6. plugs 3 & 4 look great.
> 7. plugs 1&2 sooty - dry black powdery stuff.
>
> Does this mean the front carb is now too rich?
>
> Maybe the "inspector" changed the front carb setting?
Jeff Boatright '65 Sprite MkIII __o_\__
http://userwww.service.emory.edu/~jboatri/
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