Hitchcocks Forum

I have a 2003 500 Classic. The throttle sticks wide open while in 4th gear when I open the throttle all the way open. This has been a problem for several years and I’ve polished the inside of the carburetor where the slide moves up and down, replaced the cable and it still sticks. I have to hit the kill switch, pull over and tap the carburetor to make the slide go down. It will not stick on the bench or when it’s on the engine and the engine is not runing. It acts like there is a vacuum of some sort going on when I give it full throttle. Any help or advise would be appreciated.,

Terry Boehm
USA

Hi Terry, I had this too... slightly unscrewing the carb top helped! Scary, ain't it?

Slide or carb body must be worn. Have you tryed a new spring? Might help.

Hi CAESAR ----are you in touch with any other Bullet owners nearby ?? Maybe a temporary swop of the throttle slide for another, just for elimination purposes ?? This 4th gear scenario----I take it you mean out on the road ?? How about with the bike on the centre stand and the engine put through its' paces ?? The vacuum effect actually decreases as the slide is lifted into the top section of the main body, thus less is exposed to the air and engine inlet.... Finally, how about treating yourself to a brand new carb (maybe on E-Bay USA ??), they're not that dear after all,OR}----somebody who has changed to an Amal and has a spare VM28 available ????... Best regards----

Caesar, if it sticks only when on the bike and when on almost full throttle then it is entirely possible thatthe problem may be that the flange bolts securing the carb to the head have been overtightened. I experienced exactly the same symptoms on my BSA A65 when I first bought it 25 years ago. I did all the same things as you like polishing the slide etc which made everything perfect until the carb was fitted to the bike! Open the throttle fully to make it jam without the engine running then take an 1/8 or 1/4 turn off the bolts/nuts. If it is the same problem as mine you should hear the slide snap back into position. If it is the solution take the carb off and check if the flange is perfectly flat on a surface plate or a sheet of float glass. If it is deformed then you might need to skim a few thou off to make it flat. HTH.

I'm with Mad Mike. You don't say what sort of carb it is but if its a flange mount the over tightening will pull the body out of true.

Hi Caesar,

Spent a lot of time removing burrs from the throttle slide where the throttle stop pin fouled the slide, all to no avail. The return spring was simply too weak. Finally rerouted the cable not through the casquet but directly under the tank. This left quite a large loop under the twist grip, but with no tight bends, the friction was a lot less and the slide did not stick. It also helps if at the carb end you can let the cable form a smooth arc up under the tank. Eventually, I changed to an Amal Monoblock for better looks and performance and no sticking slide problem either. Cheers TrevorCH

I tend to agree with MadMike. I experienced this on my old Bonneville due to the over tightening of the mounting flange bolts warping the carb body and pulling it out of round.

Mike, if the bike still has the original Mikarb then it doesn't attach to the head by a flang in the usual Amal way. It's attached to the head via a short length of rubber tube.

Firstly check the movement/slide in the driveway without anything on, your senses will say if all is operating right