High Speed Miss After Rejetting and Other Mods

[rich_e]

I changed to 115 main jet on my Gy2 today. I also put on a unifilter and moved clip on the carb needle to the second from the bottom (it was all the way at the top). I had previously installed an NGK plug and drilled a 3/8" hole in the center baffle of the muffler.

After all these mods the bike started and idled fine. In fact, it started right away. It used to be a bear to start when it was cold out (about 35F today). I adjusted the fuel mixture and went for a ride. I was disappointed that I had a severe miss at full throttle.

I thought maybe it was too rich so I dropped the needle to the second from the top and tried again. It still missed at high RPM. I switched back to my stock plug (nearly new) and that didn't make a difference.

I put the stock (96) jet back in and put the stock air box back on. I put the carb needle all the way up. It seemed to be better after that, but I really couldn't get a full pull as it had started raining. To top off my wonderful day I dropped the bike in the mud turning into the driveway. I didn't have the plastic on it, but it bent the clutch handle and shifter a bit.

I gave up for the night after fixing the damage.

Would a simple jet change cause such a severe miss (It was really bad almost like pressing and releasing the kill switch at high speed)? I was thinking that maybe I disturbed the plug wire too much or knocked something else lose.

[IronFist]

Hey brother what does you spark plug say. Start with a fresh plug and do a throttle chop, and read you plug. Make sure the plug gap is close to spec. Check your intake manifold for leaks. If it's letting in air, you will be too lean. Try setting the clip all the way towards the pointy end first. If you are starting better you should be rich enough. Once it's warmed up and the choke is back to it's normal running spot. Try running it, if it still sputters, try again with the choke half on this time. If it gets better, you are too lean. If it gets worse, then you are already too rich. Hope this helps you out some. N2r

[madmaximum]

96 to 115 is a big jump. Try something a bit smaller.

[TeamCheap]

I went from a 98 to a 115 but that was because of a combination K&N filter and an after market pipe that is just a straight thru open pipe basically.

So you may want to go down a bit on the main jet size as madmaximum has suggested.

[IronFist]

I did simular mods with close to the same rejetting though my plug was still a little hot/ light colored. :? Sorry if I gave bad advice, just trying to explain how to test, to see how the engine is running, rather than guessing. My bad. :oops:

[rich_e]

It was way too rich. Pulling the choke made it worse, so it wasn't lean. I'm just surprised at how bad it ran at WOT with that jet. Runs fine now that it's back to stock jetting and air filter.

Thanks!

[red2003]

That jet wasn't your problem. A rich main wouldn't make it miss. Sluggish maybe, but not a huge miss like you're talking about. I put my money on an air filter misallignment. Do you think maybe you had the K % N misalligned or it fell off slightly? It's easy to do with the clamp on filters and that WOULD make a high RPM miss. Something to think about. Now that you have it running right, try changing one thing at a time and see if the stumble re-appears.

[rich_e]

It was a foam unifilter. It was obstructed a little by the upper frame rail. I didn't like it anyway, it seemed too exposed and was getting road grime on almost right away. Do you think I may have over-oiled it? I put it in a plastic bag and pored in some filter oil and squeezed it all around. I squeezed out the excess and mounted it. Are you supposed to let them dry a while? Maybe it was sucking in filter oil at WOT.

[TeamCheap]

The K&N filter I put on mine works great but I also bought the K&N filter clean & lube kit for it along with the filter sock to help keep out the bigger stuff.

I've heard the UNI-filters are even better though.

[fatboy250]

It sounds like a plug wire to me or a coil. Make sure you're not touching the engine with your plug wire. They seem to come stock hanging out there in the breeze and ours were too close to the engine during setup for my taste. I bent the wire holder away from the engine.

Jason