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Previos own was running a desert pipe and it was popping at high end last year. Bike has since been rebuilt with new top end. FMF gold series GNARLY head pipe with an FMF tip. I am getting hesitation up high in every gear. Sounds like it is starving for something,but not sure what.
I've gone from a 145 and a 150 main jet with and without air box cover on the bike. The air box cover does have holes in it. The jet neddle is on center clipI have gone from 1 1/4 to 1 3/4 on air screw and now I'm back to 1 1/2 out. Then I went to a 158 main jet then to 160 main and no change. Had coil check by local shop and was told it was OK.
Any ideas on what to do next? Could the coil be bad even though it checked out OK. Any imput would be great!
Thanks,
Ken

check the timing? KIPS operation? Air filter clean and properly oiled? new properly gapped sparky plug? reed valves in good shape? If no air leak from bad crank seals or gaskets, could be the coil or the CDI. It would be good if you had access to another bike to swap those and test. oh, also make sure your kill switch isn't coming on from high rpm vibration, but that's a longshot.

Also, when you say new top end, you didn't put the stock piston in there I hope. They're grenades you know.

The bike has a wiseco piston and boyesen reeds. When piston blew previous owner pulled out broken piston by the bottom of the connecting rod. Is their a quick and easy way to check for an air leak in the crank seals or gaskets? I do have access to another bike so I will swich out the coil and CDI to see if that is the issue. Thanks alot for your advise.
Ken

Good on the Wiseco. Checking for an air leak is quick and easy but only if you have a rig to do it. Unfortunatley a store-bought one is expensive. Motion Pro has one for over $200. I made one for less than $20 with parts you can get from a home center. You need a low pressure gauge and some NPT fittings to create a way to block the exgaust port and pressurize the intake port. You pump it up to about 6-10 psi, and then measure how much it leaks down over a few minutes. I woiuld think some web searches might yield some examples.

could your main jet be too large...you may be getting too much fuel. If you are running the stock 33mm carb, that would be my guess but I don't know your elevation and temp range. Good luck...let me know if it's the jetting b/c I'm trying to get mine dialed in as well.

I second the mainjet check first. You can see what I run in my 220 in the bike profile below. The jetting noted works well all the way up to about 4000 feet....

Up to a 160? On a 33mm carb?

Re: 'I second the mainjet check first.'


Uh...yeah!


1. ..am getting hesitation up high in every gear.

2. Sounds like it is starving.

3. Sputtering at high end.

Those three descriptive phrases relate to different things.

The first two I could understand to be normal for a 220. One of their 'virtues' is poor breathing in the upper RPM ranges.

It is not a 12-14KRPM bike......