I have a Yamaha RX 135 which is a 2 stroke bike, and I have replaced it's carburetor , Previously it was stock 26mm round slide mikuni carb , and its been replaced with 30mm Flat slide mikuni.

After replacement bike runs very fine and and there a lot of improvement in higher end after replacement, However when I suddenly try to open full throttle, The engine makes a deep booooo sound like no air is sucked in or its being choked like bike is running out of of fuel.

Also when doing high speed , when I keep my throttle completely open, as soon as i reach my top limit, engine again stalls and looses acceleration but when using like 70-80% of throttle bike runs very well.

My main and pilot jets are stock I believe which is #17.5 pilot and #115 on main.

Can anyone please explain my why this is happening?

  • 1
    Welcome to Motor Vehicle Maintenance & Repair! May 18 '18 at 4:21
  • 1
    Its call a snap throttle Bog, it is way too lean on snap throttle, I would up the main jet. I assume this carb has no accelerator pump?
    – Moab
    May 18 '18 at 15:27
  • @Moab thanks for the response , I've also thought of same maybe because of bigger carb updrage I need to upjet my carb to match its specs. And yes , By bike is pretty old its a 1989 make so anything accelerator pump or something similar is not there , Its just carb and the engine. Also can you please suggest me a what jet size i can try next? May 21 '18 at 1:57
  • 2
    You go up 2 numbers at a time until the bog stops.So 115 to 117 to start. Its probably close at 115 so 117 may do the trick. Also if that new carb has a jet slide needle it may be adjustable also, move it up a notch or two before trying a larger jet.
    – Moab
    May 21 '18 at 22:07

As per @Moab suggested, I have tried upjetting my main jet, It helped but at lower-mid rang bike was sill not smooth enough, I tried #20 on pilot jet with #117 Main jet and my bike is running completely fine now. It was because of wrong jet size I was using.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.