Strange wear on throttle body.

[Tiesco]

I noticed this on the left carburetor today. Clearly it's from the throttle plate rubbing but what's causing it to be pulled like that? These are BS38 carbs that I have the carbs completely apart at the moment while I'm waiting for parts. Is it anything to be worried about? I can rub my nail across it and feel it.

My left cylinder runs the stronger than the right. The left always seems like its ready to go while the right seems like its just along for the ride. What I mean is that the left fires louder and smoother than the right.

 

[TwoManyXS1Bs]

Yeah, Mailman and Robinc did a lot of chasing on worn carb throats.

Have a look in here.
Gets pretty deep.

http://www.xs650.com/threads/my-60th-birthday-present.47639/page-37#post-511934

And, Robinc's "book"...

http://www.xs650.com/threads/on-the-road-again-at-40-the-bike-that-is.49360/

 

[Tiesco]

Well after reading through Mailman's thread, I can say that the wear on the throttle body is in between typical wear and Mailman's throttle body wear.

 

[5twins]

When you install the return spring on the butterfly shaft, it naturally pulls the shaft towards it. We compensate for that by installing the butterfly plates loose then holding the throttle wide open and letting it snap shut a few times. This centers the plate in the bore and hopefully does away with it being pulled too far towards the spring. I'm not sure if they did this "centering" operation when the carbs were originally assembled and that could account for the excess wear some find.

I think the only way you'll find out if yours is worn too much is to try it. If you can't tune them, get them to sync up right, then maybe it is.

 

[Tiesco]

When you install the return spring on the butterfly shaft, it naturally pulls the shaft towards it. We compensate for that by installing the butterfly plates loose then holding the throttle wide open and letting it snap shut a few times. This centers the plate in the bore and hopefully does away with it being pulled too far towards the spring. I'm not sure if they did this "centering" operation when the carbs were originally assembled and that could account for the excess wear some find.

I think the only way you'll find out if yours is worn too much is to try it. If you can't tune them, get them to sync up right, then maybe it is.

What about using a shim or replacing the plastic spacers entirely to help?

 

[5twins]

I suppose that might work. The BS34s use an aluminum spacer with a thin plastic shim between it and the carb body.