TT250 hiccup
 

I installed the aftermarket Ebay pipe, 47 tooth sprocket, opened up the air box and re-jetted the carb with a 112 main jet while lifting the needle up one notch from the stock position. The bike runs fantastic, except every so often while under load in top gear the bike sort of stutters for a fraction of a second which is like a hiccup in human terms.

It almost feels like the spark gets interrupted for a heartbeat, but I can't imagine what would cause that.

It could be the fuel gets cut off from the intake momentarily- which I don't think would feel as dramatic as a hiccup - and there really is no explanation for that to happen.

Perhaps it has something to do with the air injection system?

Has anyone else experienced this sensation? Any ideas? Thanks.

You might want to try a larger main jet.

Why would that be? More specifically, wouldn't a lean condition manifest itself as more of a constant lean situation rather than something that occurs every 60 seconds or so?

Also, has anyone tried using a 114 jet with my combination (I am at sea level)? If so, how were the results?

Sounds like it could be a main jet issue or float level problem. What you are describing sounds like at high rpms that it needs more fuel than it is getting. It's so quick to change jets on that carb that I would start there. Maybe try a 115 main. Search around as well to see if you can find the proper specs for the float height to be sure the floats aren't cutting off the fuel too soon.

True, I thought about float height also while riding. If the level was set too low I could slurp all the fuel out of the bowl before it was able to replenish itself. That would seem to make more sense.

I have 115-30 jets with similar mods on my Hawk.No more hiccups.

Is this the original carb that came with the bike? After you changed the main jet did you make sure the carb was bolted to the head, or manfold, firmly? Yes, it could be related to the air injection system, that's why some folks blank off the ais port with a piece of aluminum.

Chuck - was your bike doing the hiccups also before you increased the jet size to 115?

Ariel - yes, it is the original carb and I did re-torque the flange bolts properly so I do not suspect any leaks there. What are the 'usual' symptoms of the air injector system failing?

I'm with the others on the main jet being a good place to start. I'm at 3000' and am running a 112.5/25 (Mikuni) in Mrs 2LZ TT250. It pulls solidly all the way up the rpm range.
What elevation are you at? You may be able to easily justify a 115.

What would you think would be needed for a main jet at 8500 - 10000 feet? I have a new uncorked muffler a mikuni vm26 carb with a foam filter. Iam thinking maybe a 120?

No, you would need to go leaner at higher altitude.

The way it is now with the stock 100 jet at wot the bike sputters like its not getting enough gas.

As moparrob states, normally you go leaner in higher altitude and you're WAY up there! My suggestion would be to contact Jets-r-us and order a small variety.
What jetting are you currently running? The stock Mikuni 100/20 that came with it?

ya the 100/20. I have a set of 10 jets going from 88 up to 125.

Hiccups.