Keihin Throttle Shaft Seal

[jrp]

Hello all,

I am trying to chase down what I think to be a vacuum leak somewhere in the carbs of a 1998 ST1100 ABS/TCS I recently serviced.

When I disassembled the carbs for cleaning, I soaked each of them in Berrymans, however, I did not disassemble the throttle shaft.

I am wondering what kind of seal there is for the throttle shaft and if I somehow damaged it.

Regards,
Jeff

 

[bdalameda]

I do not believe there are any seals on the throttle butterfly shafts. None shown on the parts schematics. If you soaked the complete carb body with the shafts in place I would make sure you lubricated the throttle shafts as the cleaner will remove any lubricant and this will cause the shafts and bushings to wear out. As far as air leaks, check the small vacuum hoses used for carb syncing as well as the vacuum shutoff diaphragm. Did you remove the air cutout diaphragms before soaking the carbs?? If not the carb cleaning solution will destroy these diaphragms and seals. A leaking air cutoff diaphragm or o-ring seal on the covers will definitely act like a vacuum leak.

An easy way to find vacuum air leaks is to run the engine at idle and take either WD40 or carb cleaner and carefully spray it around the carb manifolds and suspect areas. If there is a leak the idle speed will change when you spray the fluid on the leaking area.

 

[jrp]

Thanks for the tip on lubricating the throttle shafts. I replaced the vacuum hoses and eliminated the vacuum shutoff. Yes, I removed the air cut diaphragms. I have not yet tried the WD40 method...the leak is not bad enough for me to tear too far into it...just notice it as a gradual increase in idle speed as the engine warms up. That suggests a vacuum leak somewhere. Will probably ride as is until end of season.

I do not believe there are any seals on the throttle butterfly shafts. None shown on the parts schematics. If you soaked the complete carb body with the shafts in place I would make sure you lubricated the throttle shafts as the cleaner will remove any lubricant and this will cause the shafts and bushings to wear out. As far as air leaks, check the small vacuum hoses used for carb syncing as well as the vacuum shutoff diaphragm. Did you remove the air cutout diaphragms before soaking the carbs?? If not the carb cleaning solution will destroy these diaphragms and seals. A leaking air cutoff diaphragm or o-ring seal on the covers will definitely act like a vacuum leak.

An easy way to find vacuum air leaks is to run the engine at idle and take either WD40 or carb cleaner and carefully spray it around the carb manifolds and suspect areas. If there is a leak the idle speed will change when you spray the fluid on the leaking area.

 

[bdalameda]

Most ST1100's will idle at a lower RPM when cold and the idle will increase by a couple of hundred RPM when warm.

 

[CYYJ]

Most ST1100's will idle at a lower RPM when cold and the idle will increase by a couple of hundred RPM when warm.

This is how my ST 1100 works - I have the idle speed knob set so that the engine idles at about 1,000 to 1,100 RPM when warm. When I first start a cold engine, it will idle several hundred RPM under that, and eventually the idle speed will rise to 1,000 to 1,100 RPM once it has warmed up. This is normal behavior.

Michael