Author Topic: 77 cb750 blowing air through carbs. not starting  (Read 791 times)

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Offline 77f2

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77 cb750 blowing air through carbs. not starting
« on: May 08, 2013, 08:17:16 AM »
hi everybody, long tie lurker on here but i decided to finally make an account because im at my wits end on this motorcycle. so far ive cleaned and rebuilt carbs with new gaskets and float needles. set float height. i thought the ignition was the cause but ive got it spot on right now.
bike is a 77cb750f2. when turning the bike over it just puffs air out of every carb mouth and you can physically feel it doing it.
i have spark and fuel. ive checked and double checked the valves and they are set at 0.002 and .003 just what the manual says

Offline flybox1

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Re: 77 cb750 blowing air through carbs. not starting
« Reply #1 on: May 08, 2013, 08:20:12 AM »
you might want to read through this for some hints...
http://forums.sohc4.net/index.php?topic=119499.0
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

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Offline 77f2

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Re: 77 cb750 blowing air through carbs. not starting
« Reply #2 on: May 08, 2013, 10:17:38 AM »
ive read through that whole thread and i went back out and double checked everything. when cylinder 1 is at tdc my ignition mark is on the T mark. im positive theres no bent valves. it turns over wonderfully with no noises. as far as i can tell everything is set correctly but something is wrong.
any other ideas?

Offline 70CB750

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Re: 77 cb750 blowing air through carbs. not starting
« Reply #3 on: May 08, 2013, 10:23:16 AM »
Do you have compression?

Unrelated, but I just went through it with this old hand me down mower.  The intake valve was stuck open and compression test showed me the way.
Prokop
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