I 've been up to my old tricks, just can't leave well enough alone.
I was messing around with the muffler end cap, after hearing of some good results on here, I made a pretty neat new end cap with a 1 1/2" tailpipe and some neat internal baffle/slot things, but I couldn't get it running right, even after numerous jet changes, again. (This is how the FMF got sent back, but it was too loud anyway) Am I getting an air leak from screwing around with the carb so much? I just went out and reseated the carb into the intake manifold/boot, and maybe it was just a smidgeon out. But it is getting too late to make another test run tonight.
Well I got fed up, undid and redid all the welding and put the original tips back in, rejetted and it still craps out on top. Is that an air leak? I'm talking wide open throttle, full blast runs, it craps out on top. Now I went through this with the FMF, couldn't get it, put it all back to stock except for the K&N, went from a 165 to a 170 and it ran great, revvved all the way up without crapping out on top. This time I put it all the way back to stock, kept the K&N and it still crapped out on top. Tried a 165,170 and 175 main jet. I tried going all the way to 190 with the FMF. The Dynojet needle just made flat spots mid-range, I tried it 4 or 5 times, and have changed main jets maybe 20 times now.
I'm wearing these poor float bowl screws out. What the %$@# am I doing wrong? And yes I do have the right main jet, the one in the brass shroud. Any ideas or help with this would be very much appreciated. Thanks guys,,,

 

For those of us who may not fully understand - how is your bike crapping out? is it bogging?, going flat at WOT? dying on you or what?
One of the problems I experianced early on was my bike bogging down when I had it wide open and cruising over rough terrain- have your tests been over rough terrain of smooth ground? My carb problem turned out to be the float bowl was not adjusted properly and was not supplying sufficient fuel as the bike bounced around -expound on your symptoms and give us a little more to think about.
ps. Enjoyed JYW last Monday that was quite the torpedo you guys built,
better luck next time!

 

I'm doing these tests right out on the highway in front of our house!
Hah. I've got a nice stretch of straight New Mexico Highway 211 that we used to use as a drag strip when we were kids just across the Gila river. A car comes along every few minutes, I just try to time it so I can get a good hard run. It is smooth, fast, paved, straight.
So a jet run is 3 or 4 wide open throttle, full speed runs, well over a mile each way. So when it isn't running right, I can tell at the top of first, second, third etc. It revs up and then "craps out" instead of a nice smooth high rpm. It's almost where you would shift anyway, but almost. Then I get it up to full speed, and it acts like it's running out of gas, high rpm sputtering, (float bowls?) When it's right, I must be going 80, My eyes are tearing under my goggles!
It is a wide open throttle thing, like a nasty rev limiter, which is why I have been concentrating on main jets, but I think I have exhausted that and am looking for some other cause/remedy. That's why I was thinking air leak, float setting also occurred to me, but why would that change, unless I unknowingly whacked them putting the carb bowl on and off so many times to rejet. Could it be a fuel filter? Bad Fuel? I guess it could be any of the above. I better start with some fresh gas and see if there is a fuel filter anywhere that could be clogged or even some crud in the float valve.
It's too bad I undid my tailpipe endcap thingy, it was kinda cool, and obviously not the problem.

 

After a full throttle run, immediately pull in the clutch and cut the engine off. Coast to a safe place and look at the spark plug. This should tell you what's goind on. White porcelain = lean. Sutty porcleain = rich. Light brown = perfect.
I know how you feel. We should start a fix it until it's tore up club.
Also Note: While working on your atv, certain fluids exaggerate this syndrome.

 

fourlix have you check the vent hose on the gas tank. If it gets pinched it will cut the flow of gas to the carb

 

Yeah, I kinda like Vodka and orange juice as a cleaning solution/universal solvent.

 

Hey did you notice the description under our names and icons? Yesterday I was a "weekend warrior", now I'm a "Pro Rider". Boy, we got good huh? Who's paying us?

 

Yes, certain SCREWDRIVERS work better than others when performing maintenance.

 

Okay, this morning I did multiple runs, no success. Still the same top end high rpm sputter at wide open throttle. I drained the gas in the tank and bowl, replaced with fresh super unleaded. With the float bowl off, I turned on the gas petcock, gas POURED through, I checked the vent tube, even did a run with the gas cap real loose. I'm back to the 170 main jet, which worked best before with the K&N.
I pulled the center plug for the first time, after a good hard run, chocolate. At this point I'm thinking ELECTRICAL?? Maybe it's a spazzed out under achiever rev limiter. Anyway, I've got an appointment with the dealer 150 miles away at 9:00 AM tomorrow. There goes Saturday's ride. My son wants to go with me so I'll be having lunch at Putt-Putt instead of Hooter's.

 

If you have not done it already replace those screws with an stainless allen head screw and lock washer. The first time I pulled the bowl off to re-jet I stripped the first screw so bad I ended up cutting it off with a cutting wheel It turned a 1 hour job into a 3hr job. These allen heads are great for maintenence and jet changes not to mention access to the carb bowl you'll have a hard time stripping these out. Sorry to hear about your luck with jetting I am running FMF and K@N/Dynojet W/180 main and have had great luck (I know its a bit loud, but its a 650 its OK to have some bark with all that bite!) I know its something you have thought of but I am curious to know what RPM this is happening at? I would think an air leak would be a more apparent problem throughout the throttle range. Mind boggling......BOMBOWNER.