Finally managed to stop the damn over-run surging

[keleto]

Shouldn't really work but, somehow it seems to

(on new BVF 30N3-1)

Warm up engine to operating temperature
Set idle mixture screw to the lowest possible opening (about 1/15th of a turn out)
adjust air bypass screw to get tickover at about 900-1000 rpm (about 1-2 complete turns)

Bingo. Drastic decrease in overrun surging. Idles sufficiently to avoid dying at junctions and traffic lights, with a couple of throttle blips to stop it dying. Plug color fine.

[Andy_C]

Does not work for me.

Turning the air screw until just about closed as suggested DOES stop surging but it ruins the throttle response on mine - it just will not pick up cleanly.

I have found on mine that 2 3/4 on the bypass and 1 1/4 on the air screw gives a good compromise between throttle response and surging.

Guess that not all engines are the same - the above works for me though. Needle is in the middle groove by the way.

[Blurredman]

I agree. Not only are all engines different, but all carburettors are too.

Esspecially when time and mileage has passed.

My '87 MZ with BVF 30N2.5 has coming up to 29k miles and has had the needle replaced.
My '90 MZ with BVF 30N3 has got 31k and I needed jets and needle. This particular carburettor runs great and beautifully smooth, but only works well with this particular bike. I've swapped the carburettors and get pretty similar results. Mostly that the greater engine wear on one means that even a perfect carburettor doesn't always help compensate.


Some engines feel like crap, this can be partly down to carburattion but sometimes just wear. Equally wear can occur to carburettors and increase problems like air leakage or innacurate fuelling. I have noticed my Honda CX which has 76k miles on it is slowly getting worse MPG over the years. Perhaps I should buy new immulsion tubes or needles for it...