34mm Mikuni

My bike is running great now on the above carb. After setting the timing and pratting around with needle positions etc I have realised that the 'as supplied' (Motocarb UK) mid needle position, 250 main jet and 35 pilot is spot on for my 850.

One thing though is how the power comes back in when coming back off a rolled-off throttle (through a 2nd gear bend particularly). The power just comes back in very abruptly when picking up the throttle again after being rolled off . Do others find similar or should I even be complaining? It's very sensitive on the throttle basically. Is this something that playing with different cutaways could change?

FF,,,,,,,, your right , the MiKuni is real sensitive to sudtle changes. You'll discover right away any change you make even off idle. It's apples to grapefruits from an Amal to a Mikuni. Have fun with it and enjoy the ride :mrgreen:
Jets , needle's and slides are cheap enough you can have fun dialing it in to your liking.


Tim_S

Well done Fred, another happy rider.
Mikunis do work exceptionally well, no hesitation when right.
I am not sure what your concern is... Do you mean the power improves as you roll off the throttle ?
If so, this usually means a bit lean at those revs, and improves with less air from the lesser throttle opening.
If it happens up high, then the 250 main might be a tad small.
If your concern is that you have gained better response, then don't tell everyone or they'll all want one.
Did you change your twist grip to a faster action,when you fitted the Mikuni, that too could explain your concern.
If things are running smoooth up through the rev range from idle, then I wouldn't change the cuttaway.
What cuttaway are you useing Fred. 3.0 ?
One thing is for sure and for certain.....You only need a Phillips head screw driver to remove and dismantle you new carby.
Good things come with a screw top.
AC.

Hm, I think he means there is more surge then expected for amount of throttle given when getting back on it after backing off before attacking a turn. I wouldn't like that either and did not happen on my Combat with same Miki carb, which was rather faster over all than dual Amals with race needles. There is a hop up flow and response kit for Miki single round slides called UFO that fits a streamline cap on the bottom of slide and then tuning instructions. The same place also sells a auto fuel enricher circuit thats just a extra jet and tube that makes up for altitude and temp
changes and extra fuel needs, so it says. Spark timing might be influencing this too.

If me I'd try a degree of retard then drop needle a notch, if worse do reverse, if nothing maybe a bigger jet? Might diddle float level too.

Problem: "The power just comes back in very abruptly when picking up the throttle again after being rolled off ."

Try opening the air screw. The motor will load up slightly on the overrun if the air screw isn't open enough, and then it comes in abruptly. My race bike does that. You can try it out to about 2 or 2 1/2 turns. If that makes the bike start or run badly, another thing to try is to raise the idle slightly, so that the slide is open enough to let a little air through, a fast idle like 1500-1700 rpm should be enough. If you are having trouble getting the airscrew right and the bike still starting and running slowly properly, or you have set the idle too fast, you can try to put the next size pilot jet in (no more than 5 numbers bigger, like 40 instead of 35, but preferably 37.5), return to "normal" settings, and start over again.

Thanks all. I think it may have a fast action throttle - will check and also open air screw. Like I said in the lower gears it comes in pretty abruptly and not as sensitive as I'd like for feathering power in. Not complaining though

If you can't predict and control the power exactly then it sure distracts from the fun and life expectancy. The race needles that fit Amals act like this d/t a bit steeper tapper, no change in WOT power but rather more power surge on smaller below WOT opening ups.
If just the fast act throttle then you'd feel same response getting up to speed and you'd not be annoyed by the extra surge per wrist work. Might help to mark throttle to record the zone it surges in. Its possible there is weak electrical connection that conducts fine above some rpm but not below when shakes more slower or nill G's pulled.