If I pull back on the throttle to far the throttle valve gets jammed in the open position and the spring wont push it back down. I've opened and cleaned with STP Carb cleaner over and over again. I've let it sit to dry and everything else. I do notice that there is a lot of slack in my throttle cable so could I be pulling it up to high?

'71? I think that's the model with a flange and two studs holding the carb on, unlike later ones that have a rubber connector and hose clamps to hold the carb. Do you know what I mean?

If so, sometimes the carb got put back on the bike without the gasket and/or the nuts on the studs got over-tightened. This distorted the carb body and put the slide hole out of round. The slide then sticks as it gets to the asymmetrical part of the carb body. It could be this.

If so, its a fairly easy fix, but it will take time. You need some fine wet and dry sandpaper, about 400 or 600 grit. Take the carb apart, and remove the slide off the end of the cable. Look inside the bady where the slide goes and see if you can find the marks where the slide is scraping. Using the wet and dry paper with water, rub away until the slide, well, slides!

Sometime even easing off the stud nuts a half turn both sides can "un-flex" carb body enough to free things.


Regards

Nigel in NZ

__________________
The mouth of a perfectly contented man is filled with . -- 2200 BC Egyptian inscription

Both me and my buddy will had this very same problem with the Mikuni carb. We tried fine grit sandpaper but found that the easiest solution was to get a much stiffer spring. That will keep the throttle from sticking and wear everything down to the point that you can eventually remove the stiffer spring.

We used springs from some cheap airsoft toy guns (very stiff).

Good Luck