Sticky throttle, anyone ?

[Richard Negus]

Does anyone else have a throttle that sticks 'shut' as an IP2 or Classic engine cools down ?This average-mileage IP2 has new butterflies, spindles and bushes but, occasionally, I find the twistgrip won't move when the engine is cold. Giving it a sharp tweak frees the stuck butterfly - but also upsets the throttle balance so that it becomes rough and idles at a higher speed.Anyone got any bright ideas that don't involve stripping the engine, or even ANY ideas ?

[gripper]

Without seeming to ask the obvious. Have you eliminated the twist grip and cable/junction box from your investigations? Then if you increase the gap on the adjuster screw between the two butterflies you could then maybe identify which butterfly is the culprit.

[MrB]

Since you've asked for ANY ideas, it sounds like the aluminium might be expanding, a disc then closes and is gripped by the aluminium as it cools and contracts. Why this one though and not others - has the disc worn the beginnings of a ridge in the intake tract? Is there a slight flaw / bimple in the casting that just catches the disc?Johnny

[andy588tt]

Hi RichardWhen I was in the motor trade and a SU Carb was sticking after checking butterfly spindle body for movment we would put Red X in the fuel tank. Red X tin will advise on the quantities ! It will smoke but after a couple of fill up you should feel a difference. best done on a long run The theory is Red X has a higher melting point then other oils and will lubricate for longer. Ride SafeAndy

[Malc]

The red race bike used to suffer from this and fitting new spindle bushes and checking all the obvious didn't cure it. The problem was worse the hotter the engine became during a race, running 150 to 175 on guage. Would stick within a couple of minutes sometimes but was using oil pump on max setting and pre-mix in tank.Answer was to put choke on while engine cooled as fast idle rod was adjusted to hold butterflies open enough.Also had to do the same on other road bikes with same problem.Another anomoly! The silver track bike (having not neen started for 2 years) was run at Anglesy.The engine is modyfied more than the red one but it has such a superb tickover at 800rpm, fixed fully advanced and the pick up is even more responsive than the road bikes with the light flywheel. Needs to be run at 150 degrees or higher to run cleanly at higher rpm though. This also had new throttle spindle bushes when built and the throttle is set up the same way as the red one and runs the same pre-mix but no sticking throttle problems.Malc

[Interpol2471]

Take it to pieces Richard you know you want to...!!!!

[johnbirchjar]

Hi Richard,I've had this problem on the Classic for years!! all I do to alleviate the problem is to pull the choke out first,then push it back in, and this free's up the throttle,I've never forced the throttle for fear of pulling a nipple off,and seeing as I have neither the inclination nor the knowledge to pull the thing to pieces the "status quo" will remain,regards,J.B.

[Richard Negus]

Thanks for all the feedback.Since this is a recently rebuilt engine, I can't leave it hoping to remember to pull the choke before it cools. Original butterflies had a Xylan coating (some sort of ptfe ?) around the edge, presumably to stop them sticking, but since I haven't seen it still there on stripped engines, I guess it doesn't last very long.Option 1 seems to be to make some new butterflies which are longer on the major axis and seal at a different place in the port.Anyone know anything about Xylan and where to get / how to apply ?