Carburetor "tuning"


Staff member
477 Owner
22. July 2021, 12:25

I lifted this from the advertising forum where Beemerboff shared his insights, however I have a few of my own:

My Oz model has a UCAL UCD 33-D1 BY20 carb, which actually measures 32mm at the motor end.
Some claim it came straight off a Bullet, with no changes whatsoever, but who knows.
Just a reminder to any who might be considering the carb conversion to remove the float bowl and familiarize yourself with the factory float position as the manual setting is for a Mikuni, which is very different.
Might be wise to mark the factory setting for the TPS too as the carbed bike manual gives no information.
Then measure it and let us all know what it is!
Jets do little on a CV carb which runs on the needle 95% of the time, unless the main is to small for the flow in transition and softens the mid range response, not the top end as you might expect.
Pilot jet only comes into play as the throttle butterfly passes above the outlet, just as you open the throttle, so if you have a clean pick up from idle it is usually OK
CV carbs are to an extent self regulating, so if it runs cleanly across the rev range with no hickups or flat spots then minor changes are unlikely to make a noticable difference , despite what the guys who sell a couple of jets as a power kit might claim.
On my Oz bike the carb is as close as you will get, clean and responsive all the way through, so if things are not as you might expect I would look elsewhere before messing around with the stock settings.
Yes, the 500 UCE Bullet has the same carb as the Hima.

Yes CV carbs do self-regulate to a great extend unless you deprive them of oxygen

So "if things are not as you might expect" you may also look at your gps/altimeter and if it shows above 2000m (which it will anywhere in Ladakh) all of this is untrue. Unless you change to a smaller main jet (suggested 110 vs. 125) you WILL lose a lot of power, the engine will burn very rich, you have black sodd all over your right box and luggage and a spark plug that is close to none functional due to carbon residue. This is even more true if you have a 477cc.