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Hi,
I have an 85 Yamaha 700 Maxim that use to run good. I was having idling problems and high revving when making turns so I decide to rebuild the carbs. I took them completely apart and cleaned all the non-plastic and non-rubber parts with gumout then blew out all orifices and holes making sure that everything was clean & clear.

After putting the carbs on the bike and starting it I found it to run and idle the best it ever has. It had great throttle response and returned to an idle quickly. After playing with the throttle for a minute or two I decide to let it run for a little while. I walked away to do something and a few minutes later the idle suddenly started going up until it got 6000 rpm's and stayed there.

I was just getting ready to sync the carbs and fine-tune them with vacuum gauges when this happened.

Now my first thought was a vacuum leak so I sprayed gumout around the intake manifolds, the carbs, & the air breather, but to my dismay it did not have any affect.

Any idea’s ???

Thanks for any and all help !!!

Do you have a filter on the fuel line between the tank and the carbs? My guess is some gunk or dirt in the tank got into the carbs, or something close to that since your leak check didn't work.

Racing idle is usually a vacuum leak... or WAY lean. Are you sure the carbs went back together correctly?

Hi,

I do have an inline filter so that didnt happen. But gunk in the fuel would stop it from running not make it rev to 6000 rpm's. Unless Im missing something.

Thanks

Hi Sev,

Im pretty sure they are together correctly. But you can never be 100% sure. And I agree that revving is usaully a vacuum leak. And it may still be but I sprayed everything pretty heavily and it didnt even drop a little.

Thanks

please tell me you didn't spray gumout on anything rubber?

Hi Everyone,

Thanks for all the suggestions. I got the bike running perfect today.

The problem was I was using a lawn mower gas tank to tune the carbs but the real gas tank uses a vacuum valve to regulate gas to the carb's.

Without the vacuum valve gas was filling the float bowls and over coming the float valve letting gas go straight up into the primary jet acting like the throttle was open.

I have used this same lawn mower gas tank on every bike I have ever worked on but this bike requires the vacuum valve to work correctly.

Again Thank for all the help !!!