Keihin PWK 30 Carb

[Megadan]

Originally Posted by Mychel

I have issues with my hawk 250 , I live in IL.
Mods are Exhaust system.
Mikuni carb jetted to a 115 Main, needle is at middle position. I have. 17t front 40t rear I drove it wide open at in 4th gear it stopped pulling at 50mph. In 5th gear the bike had no pull at all . I came to a stop and my engine would not idle. I rev it up engine sounded like a miss fire. I got gas let it cool down and it ran a little better.
I need to know who else has 17 40 gearing and your top speed?
I need to check my plug, and any ideas on my jetting?
Thank you.

First off, as Jerry mentioned, have you set the valve lash?
Secondly, how many miles on the bike? If it has under 1k miles, it isn't going to have a ton of top end yet, especially if you are around or less than 500.

As far as jetting, what size pilot jet do you have? I always recommend a good starting point for the Mikuni clones with an intake and exhaust with a 25 pilot, needle at the 4th notch, and 115 main. With full mods even the 25 can prove to be a touch lean so a 27.5 works better.

From the symptoms you describe, it sounds to me like you started to overheat the cylinder. Fueling will play a big role in this, and if you are at a low enough altitude you may need to step up the main jet size. I would begin with the previously mentioned jet settings though. Air cooled motors like fuel when pushed hard, it helps control cylinder temps.

A side suggestion - if you are going to push this motor that hard with tall gearing it would be a good idea to invest in an oil cooler. It makes a pretty good difference.

Originally Posted by JerryHawk250

I run 17/40 gears and have done 75 mph+

bear in mind we also have ported heads and he doesn't. Anything past 70 is a tall order for a stock Hawk with just an exhaust and mikuni clone.