High Speed Miss After Rejetting and Other Mods

rich_e · 02-16-2008, 11:19 PM

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 · 02-17-2008, 10:06 AM

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 · 02-17-2008, 11:46 AM

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

TeamCheap · 02-17-2008, 12:24 PM

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 · 02-17-2008, 03:55 PM

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 · 02-17-2008, 08:07 PM

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 · 02-18-2008, 03:07 PM

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 · 02-18-2008, 03:46 PM

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 · 02-18-2008, 04:25 PM

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 · 02-19-2008, 08:10 AM

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

02-16-2008, 11:19 PM	#1
rich_e Join Date: Nov 2007 Location: Kansas, USA Posts: 228	High Speed Miss After Rejetting and Other Mods 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. __________________ 2000 HD XL1200C 2006 Hi-Bird QH-250-GY 2004 150CC Dual Sport (Chongqing Xgjao) 1978 Honda CB750K 1977 Honda GL-1000 (Goldwing) Project/Parts bikes 1977 Honda CB-750K 1977 Honda CB-550F
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02-17-2008, 11:46 AM	#3
madmaximum Join Date: Jan 2007 Location: Central PA Posts: 284	96 to 115 is a big jump. Try something a bit smaller. __________________ 2005 RSX-200E 2004 Suzuki Eiger 1999 Arctic Cat 250 1977 Kawasaki KH400, aka Green Ripper
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02-17-2008, 08:07 PM	#6
rich_e Join Date: Nov 2007 Location: Kansas, USA Posts: 228	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! __________________ 2000 HD XL1200C 2006 Hi-Bird QH-250-GY 2004 150CC Dual Sport (Chongqing Xgjao) 1978 Honda CB750K 1977 Honda GL-1000 (Goldwing) Project/Parts bikes 1977 Honda CB-750K 1977 Honda CB-550F
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02-18-2008, 03:07 PM	#7
red2003 Join Date: Jan 2007 Location: Northern Vermont, USA Posts: 1,218	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. __________________ 2006 Roketa RSX200E MODS: YZ250F Muffler, Airbox delete with K/N style filter, Main Jet reamed 2 sizes over, Yamaha R1 Rear clicker shock on custom scissor linkage making 8 3/4in. of rear wheel travel!!! Battery relocated under seat.
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02-18-2008, 03:46 PM	#8
rich_e Join Date: Nov 2007 Location: Kansas, USA Posts: 228	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. __________________ 2000 HD XL1200C 2006 Hi-Bird QH-250-GY 2004 150CC Dual Sport (Chongqing Xgjao) 1978 Honda CB750K 1977 Honda GL-1000 (Goldwing) Project/Parts bikes 1977 Honda CB-750K 1977 Honda CB-550F
	0

02-17-2008, 10:06 AM	#2
IronFist Join Date: Apr 2007 Location: Toronto Ontario Canada Posts: 2,585	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
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02-17-2008, 12:24 PM	#4
TeamCheap Join Date: Jun 2006 Location: directly under the earths sun............NOW Posts: 2,302	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.
	0

02-17-2008, 03:55 PM	#5
IronFist Join Date: Apr 2007 Location: Toronto Ontario Canada Posts: 2,585	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:
	0

02-18-2008, 04:25 PM	#9
TeamCheap Join Date: Jun 2006 Location: directly under the earths sun............NOW Posts: 2,302	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.
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02-19-2008, 08:10 AM	#10
fatboy250 Join Date: Sep 2006 Location: COLUMBIA, SC Posts: 973	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 __________________ 2008 Jonway MC-70-150 2007 Roketa DB-07B (RSM-200E) 2006 Roketa DB-07A (RSX-200E) 1995 Kawasaki Concours (ZG1000)
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