Motorcycle Safety & Driveability: Carb Linkage, linkage area, linkage problem

Question
I have a '75 Yamaha 650. One of the carbs has a linkage problem at the point where the circlar spring controls the rpms.  When you give it gas, it increases the idle but doesnt idle back down. The other carb works fine.  I have noticed that the exteriore parts are rusty. is there a good lub product to use. Is there anotheer problem perhaps?
thanks

Answer
Hal,

Thanks for the question. I had a 76 Yamaha 650 twin in college, it was a neat bike, lots of torque, good sound, decent if not stellar handling. The girls seemed to like it!

The most likely problem is that if there is rust on the outside, there's a good chance it's on the inside as well. Squirting a little WD-40 into the linkage area might loosen it up in the short term, but what is really needed is for the carb to be taken off the bike, the linkage taken apart, all the parts cleaned of corrosion (and replaced if too far gone), and then put it back together. And if you're going to do one, might as well do both.

This does NOT qualify as a "carb cleaning". Sounds like the carbs are mixing the fuel properly, so you do not need to get into the nitty gritty of cleaning the interior of the carb(s). However, this bike is 30 years old, and no matter how well it's been taken care of, parts are going to wear out, if not from use then from age. Disassembly and cleaning may be all that's needed. Be sure to check the return springs to see if they are broken, or are about to break. Or they may just be stretched out. But it sounds like some corrosion has gotten into the rotation axle of the circular spring, and it does not have enough tension to overcome the friction.

If you feel that taking the carb assemblies off for cleaning is beyond your ability (no shame in that), check around the area for a mechanic who will do it, maybe a dealer mechanic will help you "on the side" (and on the cheap).

As for rusty surfaces, I DAB (not SPRAY) on some WD-40, let it sit for about 10 minutes, and then scrub the area with a small wire detail brush (get them at auto parts stores). A shop rag or old towel cleans off the dislodged rust.

Your sticking carb return linkage is not a big problem, don't be afraid to take the carbs off and give them some attention. Make sure you turn off the gas petcock, and drain the carbs of gas before removing them. And, of course, no smoking while doing this maintenance.

Ride smart, good luck,

Bill Roberson