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1981 cb750 f problem

annunz1ata

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My 81 cb750f isnt running so well at high speeds. When I'm in 5th gear on the freeway it seems to lose power around 90mph.. an i have to let the rpms back down and baby the throttle, it seems to catch and bucks a little bit, like there's too much air comming in as opposed to fuel. For a minute or two i cant go over 65mph before it catches again... then i have full power. Any ideas? thx.
 
make sure your fuel cap is breathing ok. could be blocked. this would cause a starvation of fuel at high revs. worth a try.
 
It sounds like fuel starvation. I get this at low speeds before I have to switch to reserve. Put some seafoam in with next tank of gas (1/3 bottle I hear). Repeat. Try draining fuel bowls on carbs to see if you have any kind of massive rust coming from the tank.

It sounds like the vacuum for fuel pumping isn't able to keep up. Maybe some rubber is going bad, or something gets blocked. Why at high speeds? I don't know. Pods? This is identical to having your fuel turned off, riding for a block, having it putter some, turning fuel on, and in a minute or so it'll be pumping the right amount then take off.
 
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