turn the bike on and it instantly revs

[estewart]

so i rode over to a friends house and as soon as i get there i notice fuel dripping out of the back of my carb, i figure no problem its done it before and its an easy fix, i take them off and tweak with the floats and needle, put it back on and it stopped leaking.

when i go and kick the bike over (start it) it revs like crazy. i stopped it and checked my idle set screw and backed it off, found my vacuum line unhooked and plugged it in. started it again and it still revved, this time i took my pod filters off and checked to see what was going on. both butterflys are closed along with the slides. throttle cable moves freely, and i went ahead and unscrewed the idle set screw as an over adjustment. but it still revs. the odd thing is when i put the choke on, the rpm drops to a near perfect idle.

it has never done this before and and has me stumped. i figure it could be a vacuum leak but haven't thoroughly checked it, so i'll be doing that next.
any other ideas on where to go and what to do next?

 

[BigJimmyW13]

When mine was doing that it was because it was sucking air in at the intakes. Hope this helps man.

 

[angus67]

mine does it after warm up. new boots, capped the vaccuum ports. dont know. sound like vaccuum leak to me

 

[gggGary]

Don't know which carbs you have but an out of adjustment synch screw can hold one side open. Narrow it down, pull one plug wire then the other (keep a grounded plug in them.) see which side does what.

 

[estewart]

thanks for the responses, turned out it was a vacuum leak, i took the carbs off and cleaned the mating surface of the intake manifolds and replaced the vacuum hose that goes to the petcock, i also noticed my vacuum port cap was showing cracks in it, replaced it and it was good to go.

 

[Ironsled77]

I had a cb750 that did that. It scared the shit out of me with straight pipes!

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