Throttle butterfly valve sticking inside throttle body - advice?

Hey all,

I've had a sticky throttle for a while, and after taking the throttle grip apart, lubing cables, etc etc, it seems like the culprit is probably the butterfly valve inside the the throttle body. We tried slightly loosening and attempting to recenter the butterfly to make sure it's not hitting the sides of the throttle body, and it seemed like we'd improved/fixed the problem in the garage, but on my test ride the thing stuck really tight at nearly wide-open throttle and sent me rocketing at 70mph through my neighborhood, forcing me to hit the kill switch (and crap my pants).

Soooo...

Anybody ever replace one of these? Does the entire throttle body have to be removed? Do you just replace the butterfly, or do you buy a whole new throttle body unit? Any advice, suggestions, prayers...?

—KC

How many miles are on your bike and year? Best way I can say to find the problem in your throttle system is to isolate each part and make SURE they are in working order. U said you disassembled the throttle/grip assembly and that was okay. Good, now I would remove the airbox, inner airbox, and velocity stack. Loosen your cables and remove them from the throttle body assembly. Now make sure they move incredibly easily with no binding or catching back and forth. John tells me these cables seldom fail, but if they feel like they drag or catch replace them a worn out cable can't be fixed no matter how much damn lube u shoot down it. (Learned that on boats..)

If you're good there then I would first clean the throttle body as best u can with it on the bike. Rags and carb cleaner and some finger work that the misses might appreciate you should be able to get it cleaned up fairly well. If it sticks open. Or closed by itself I would have to wonder if the rod for the throttle plate is hanging up in the throttle body from years of wear?

Thanks for the reply, BuellyBagger. My Uly is an '08 with about 45k on it.

We did unhook the cables, though now I feel like I should probably do that again just to confirm that they were indeed moving nice and smooth.

I've cleaned the throttle body inside and tried to lube that butteryfly up, too, though maybe not to the super-sexy degree you're talking about. I'll give that one more shot before I go with the nuclear option, too.

That said, it does seem like it's something going on with the butterfly, like the plate is slightly off center and catching on the wall of the throttle body, or the rod is sticking somewhere as you suggest, or something. I thought at one point I'd read about this being issue, either on here or on BWB, but I can't find the posts now, of course.

great info Cody as usual. let me add a few things here as i've run into this before with both XB's and XR1200's:
1-you have 2 cables. forward facing one is the puller...rearward facing one is the pusher. the pusher cable never ever goes bad. when the puller cable does it typically frays just inside the handlebar throttle assembly housing a tad downstream from the ferrule. the ferrule is what attaches the cable to the twist grip assembly. any signs of fraying on that cable and it must be replaced immediately.
2-if the throttle body housing is worn where the butterfly shaft goes thru it CAN be re-bushed but typically a real PITA to do correctly. i just replace the entire TB in lieu of rebushing it. how to tell if substantial wear exists there? simply disconnect both cables, wind up the butterfly to full open, and grip the end of the butterfly, try to wiggle it up and down, and see if there's movement. if so the bores in the TB are heavily worn.
3-one last thing to check if it is only sticking at WOT: the "max open" adjustment screw on the TB. the early XB's and most tube models don't have that adjustment screw....some of the later XB's do....others simply use the cast-in aluminum tang as the throttle wheel stop. if it has backed out it will allow the butterfly plate to rotate past max open position which jams it. check to see if your TB has one and if so adjust it and red loctite it. if not check the aluminum tang which stops the throttle wheel from rotating past max center point. have seen the wheels get burred and nicked and hang up on the tang. see pic. the tang is circled.
NOTE: i'm betting you either have a cable hanging up or have mis-adjusted the butterfly. do you know how to properly adjust the butterfly????





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Awesome info, thanks! I didn't know about the max-throttle adjuster, I'm guessing an '08 Uly would have that if it's on later models, so I'll have to look. It does seem to happen mostly at really wide throttle opening. The only butterfly adjustment we ever did was last time we tried to loosen those little tiny bolts that attach it to the rod (which are suuuuper tight) and shift the position of it to prevent it from sticking. It felt pretty decent once we'd done that, so we put everything back together, but then when I test rode it, I whacked the throttle WFO and it stuck so tight that I had to hit the kill switch, I literally couldn't close the throttle with my hand until I shut the bike off!

The only butterfly adjustment we ever did was last time we tried to loosen those little tiny bolts that attach it to the rod (which are suuuuper tight) and shift the position of it to prevent it from sticking.


that's the problem right there. those 2 butterfly screws are installed and then peened over at the factory to keep them tight. your plate is crooked assuming all else i told you above is up to snuff. the only way i know of to set the adjustment correctly for the butterfly plate in the throttle shaft is to unhook both cables....put a coating of grease around the bore of the TB where the plate rests when fully closed.....loosen each plate screw just a small amount....gently let the shaft go to full close....then center the plate and fully tighten the 2 screws. after that simply look down the bore of the TB and work the throttle from fully closed to wide open and see how it feels. when you have it working properly wipe away the grease. the film of grease cushions the plate against the TB bore when doing this adjustment.

Smart idea with the grease. I would also think the grease would have good witness marks to show bore to blade contact. Can tell John has been in the business a while.

Lunatic is right. Since you backed out the staked screws in the throttle shaft, they could very well loosen up and fall into the engine now.

IMO, I would get a new throttle body assembly, new cables, and be done with it:eagerness: Stuck at WOT is no good for you or anyone in your path!:eek-new: