Need Help! bike idles fine but wont rev past 1/4-1/2 throttle

[B-Hard]

So about a month ago i did 3x3, jd jet kit, fuel screw and mrd ssw.(160mj, stock pilot, screw 2.75 turns out) Bike has been running perfectly and getting better gas milage than i got before with awesome power until just yesterday. I ride to class every day, at the end of the day yesterday on the way back home i went to pass some one and once it started revving higher it almost died, where as just the same day i had driven it and it was totally normal revving as high as i tried to take it.

But after that it would not rev up much at all. It still idles perfectly fine and actually has the same awesome throttle response if you just twist it quickly, but when i try to rev it higher it cuts out and drops to idle and surprisingly doesn't stall. Its not rideable tho because under any load when i give it more throttle it just boggs down to idle and feels like it stalled, but not quite.

Only thing i could think is maybe water got in it because the night before it rained hard and i forgot to cover it, but the next morning it ran fine. I drove to class, back home, back to campus then heading home again is when the problem happened. (home to campus~ 3-4 miles)

any ideas or help would be appreciated! thanks

[B-Hard]

Well just as some info for anyone that wants to help, I drained the float bowl after reading their might be water in it, and drained the fuel line and some of the gas from the tank and started it back up. It still idles the same and will rev off idle fine, even if i floor it from idle it revs up some then stops at what i would guess is 1/4-1/2 of the rpms it should rev to before it cuts out and just drops to idle.

If i hold the throttle open past half throttle it revs to the same point, drops to idle then will jump after a second but only for a split second. just starts to rev again but then drops to around idle/almost stalled out.

Any ideas what it could be??

[B-Hard]

Bump, I really need some ideas or help for this, Idle and for first few hundred maybe a thousand or two RPMs it runs like normal but it will not rev over that and drops to idle when trying to rev higher than that.

[robw122]

a few things come to mind.

like you said, water in the fuel is a possibility.

a plugged main jet.

the spring in the diaphragm popped out of it's little clip, letting the needle bounce around or it's stuck down. the spring is crooked in the carb and the slide can't rise.

something is stuck under your seat blocking your intake. (like your hat or something random).

good luck!

[jtiv19]

Have you checked your oil for a strong gas smell?

[B-Hard]

Ya i checked the oil still just oil no gas and nothing is blocking the air box. I guess later this week I'll be pulling my carb apart as a fall break project. I'm thinking it may be the main jet

[Steve Browning]

I had a very similar issue with my bike, would ride like normal until you opened the throttle more than half way.

Tried to drain the float bowl, but no improvement, so removed the carb & found a small "lump" of residue blocking the main jet.

You maybe able to remove the main jet with the carb insitu, if you have patience & a deepish 8mm ( I think, maybe 6mm ) socket. It would save a lot of effort to do it this way, but if there is some crap in there it would be worth while stripping & cleaning the carb.

[B-Hard]

yeah after reading some other stuff and it sounds like it could be the main jet, I was just hoping i could get some other things to check b4 pulling the carb. I'm able to get it pulled in about 5 min or so and put back in the same if i'm able to line it up easly, but I always have trouble with the throttle cables.

And I'd hate to pull it, disassemble, clean an replace it only to find the same problem exists so I want to be sure its not anything else.

But my fall break starts after tomorrow so thursday I'll have something to keep me busy!

[CobbMtn03Z]

check the needle retainer,

pull tank, rotate carb a little, remove carb top( be aware of little o-ring)

most likely during rejet, didn't snap in fully, or broke some tabs on holder when reinstalling

[B-Hard]

Well my brother's bike (exact same as mine except diff exhaust) had problems with the needle, the spring didnt clip right or something but that little spring ended up popping out and the needle was free floating. My bike runs nothing like his did when that happened, his wouldn't rev up from idle well but higher rpms was a little better, and his idled rough. I'm thinking my problem has got to be around the main jet area if its not anything electrical.

[Craigo]

Checked the Main Jet for blockage yet?

[B-Hard]

Checking tomorrow, it will be my first free day this week cause of school.

[B-Hard]

Well i took it apart and sure enough there was something in the main jet, cleaned it out, and sprayed the whole carb down with some carb cleaner to clean off the outside dirt and any deposits. BUT now it has no top end. It will rev up high then start missing and not get to red line. The upper part of top end is totally gone and it seems to have a 'rev limiter' lower than before. What could be causing this?? Only thing different from before i took it apart is that i sprayed the whole thing, inside and out, with carb/choke cleaner.

Edited October 7, 2011 by B-Hard

[npm]

What kind of cleaner was it? Some of that stuff can be hard on rubber parts.

[B-Hard]

It was auto zone brand carb and choke cleaner. What rubber parts could go bad to make it run like this? Also what about the electrical plug on the carb? What does that control and could carb cleaner in it make it run like this?

[robw122]

the plug on the carb is the throttle position sensor. ignore it. most likely there's a small piece of something still stuck in the main jet or pilot jet or more in the emulsion tube. (that's the brass tube that the main jest screws into). another possiblity: whatever got into your main jet likely got there through your float valve. when you clean a carb, you need to remove all of the little brass parts and finish the job by blowing them out with compressed air. to remove the emulsion tube, you need to take out the main jet, take the top potion of the carb off and lightly press the tube up into the top portion of the carb. there are a series of small holes in the sides of the tube as well as the main hole in there. while all of the jets are out, blow out all of the passages. the tube has a locating slot, make sure you line it up correctly when you reinstall it or you'll break it. remove the pin that the float pivots on, and take the needle valve out if it doesn't come out with the float. there may be a small screw that holds the brass portion in the carb. carefully take that out and very gently (probably with a delicate hand and a small set of pliers gripping on the OUTSIDE of that brass valve), pull it out. there's a small o ring on it and there might be a screen on top of the valve. blow these out as well, moisten the o ring and push it back it. put everything back together and try again.

when all is said and done, if you find that there's junk in there, you need to find the source, be it the petcock or degraded line, w/e. put an inline filter in there to keep it clean while you have it all apart.

[B-Hard]

Well i really think the problem has to do with the cleaning i did yesterday. My brother has the exact same bike and when he did his jetting at the same time he sprayed the outside of the carb and parts of the inside with carb cleaner then upon re assembly it ran the same as mine does now, and his has been like that since. And when i did my rejet all i did was put in the jets and it ran beautifully until it got dirt in the main(which i found was because the boot wasn't totally sealed on the air box end of the carb) And after spraying with carb cleaner now mine runs like his does and doesn't have much top end to it.

I know the main is clear i sprayed it a bunch by itslef, but either way i'll still try the stuff you said just to be certain.

[robw122]

Well i really think the problem has to do with the cleaning i did yesterday. My brother has the exact same bike and when he did his jetting at the same time he sprayed the outside of the carb and parts of the inside with carb cleaner then upon re assembly it ran the same as mine does now, and his has been like that since. And when i did my rejet all i did was put in the jets and it ran beautifully until it got dirt in the main(which i found was because the boot wasn't totally sealed on the air box end of the carb) And after spraying with carb cleaner now mine runs like his does and doesn't have much top end to it.

I know the main is clear i sprayed it a bunch by itslef, but either way i'll still try the stuff you said just to be certain.

"because the boot wasn't totally sealed on the air box end of the carb"

stop taking your carb apart now and take the airbox cover off and go see if your bike runs better. or loosen that snorkel back up and pop it off half way and see if it runs better. see where I'm going here? just because your bikes are jetted the same doesn't mean you both don't have them jetted wrong.

[B-Hard]

My bike is jetted right, read the whole thread. I have tried everything with taking the air box cover off, or tape over the hole. It ran perfect after my re-jet, and did for a month until it got dirt into the main jet. After spraying the whole thing down with cleaner and cleaning the jet it now runs better than when it got clogged but not as good as when i first did the jet kit. and the air box was totally sealed right after the re-jet, but over a few weeks it slipped off some how.

I know mine is jetted right, something else is wrong now.

[npm]

It was auto zone brand carb and choke cleaner. What rubber parts could go bad to make it run like this?

Here is another thread where E.Marquez mentions the parts that can be affected by carb cleaner, post #11. I don't know if the cleaner you used was the kind that eats the rubber parts but I mentioned it as something you could take a look at if you didn't find any other issues.

https://www.thumpertalk.com/forum/showthread.php?t=1017276