1979 yamaha xs 400 help

[adam]

we have an old yamaha xs 400 and when we start it up it idles good as soon as you touch the throttle it revs up and stays at a higher rev and sometimes as soon as it warms up it does it to. we have cleaned the carbs the carb boots had cracks in them so we used silicone type sealer to seal it.
Thanks any suggestions would be greatly appreciated
Adam

[Six Stroke]

Ww had an old Honda CL450 that did this too. The problem as far as I could tell was the slide blowing open at low RPMs. They're a diaphragm type slide, so they're pressure controlled instead of being connected directly to the throttle cable. It's hard to pinpoint why it does this, but I'd check to see if you have even compression and check for air leaks. Also, check to see that the diaphragms are in there properly and that the slide is moving freely.

Another thing to check is to make sure that the cable isn't hanging up at the splitter junction (considering it has one.)