2021 TT250 carb change.

[Bob Kelly]

Hi everyone !
I recently put a 30mm Nibbi carb on the TT250 and I just wanted to tell you about it.
the manifold that I got along with it didn't work as the carb would hit the frame
(yes there is a rubber hose like connector between the manifold and carb but it would not flex that much without popping out.)
so I made my own intake manifold.... even if the manifold had worked I would have to have added a vacuum port to it as this CALIFORNIA version has a carbon canistor on it.
so I made my own intake manifold out of a scrap piece of 3/16"plate and a short piece of 1" water pipe.... and a tiny piece of brass tubing for the vacuum port.
then came the problem of hooking it to the air box.... after several false starts. I finally used a 2" piece of PVC water pipe cut and plastic welded the part to connect to the carb by a rubber hose and hose clamps
and then wiring the far end to the intake box in a dozen places and then finally using a piece of PVC from the same pipe to cover the rest of the hole in the air box then I finally used Shoe Goo from Walmart ( best liquid rubber I know of) to seal up the big hole I had made in the air box getting it all to fit
....
I had put the smallest jet in the carb that came with the Nibbi carb and gave it a try.... it started easy and ran fairly well but it stumbled around the 4000RPM mark.... I took it for a short ride and I was impressed it had alot more power on bottom end.... but at 4 grand it was obviously too lean
so I then raised the jet needle in the carb slide by the clip ( moved the clip down one notch) and tried running it again.... the lean area at 4 grand is no longer there.... so I may have hit on the combonation to make it work but I am not completely sure yet.... it's cold here and it was late at night so I will test ride it tomorrow and then do another plug color test....
...
in short there is a noticable increase of power but not enough to wheelie the bike without dumping the clutch... it has a noticable amount of grunt now
where before it didn't seem to increase in RPM's very fast when lugging it in 3 or 4th gear and going slow.....
I did have to adjust the idle air screw as from the factory it was way too lean.... I adjusted it to fastest idle at 500~800RPM and then the bike started realy easy.
....
I've noticed something funny about this carb though it seams that some times it fires up when it's cold and shuts off the choke automatically
and other times I have to turn the choke off by pushing it down with my finger..... if it is supposed to stay on till you turn it off it doesn't do that
if it is supposed to turn off automatically when it starts it doesn't do that ...so I always check it to make darn sure it's off.... or if it won't start I check it to make sure it is still on !!! if it's on the bike starts easy if it turns itself off and the bike is cold it plays Hell starting !
....
anyway I hope to take it for a run tomorrow and see how it goes
it's already a big improvement getting rid of the 26mm carb that came on it and adding the 30mm carb to it.... but it is not a bolt on thing the TT250's frame is in the way for that..... perhaps one of the other manifolds would work... I don't know I didn't try them, I just made my own !


.....
Bob.......