New Member. 1979 CB750K

[Pva68]

Hi members and visitors,

I am Paul, from Sydney, Australia. I have just picked up a 1979 CB750K with a RC04 motor. My friend has done a lot of work cleaning things up but never got it running right, got frustrated, sold it to me.

Currently has erratic idle, and wont go over 5,000rpm once hot. Since I got it it starts fine on choke, but I cant get it to idle off choke.

My first check is going to be valve clearances, then once that is known good, trying to get the carbs sorted. Mixture and sync.

Have read quite a few posts already and my head is swimming with new info.

I have a few other bikes, an '88 GPz1000rx, a '99 xvs1100 bobber, a 99 Kawasaki Drifter, and a 2018 z900rs cafe.

Looking forward to chatting to many of you over the next few months.

 

[amc49]

Shoot for .005" instead of the service manual figure of .003", the engine will love you for it. The valves leak to not let engine rev out fully, a compression test verifies it.

The carbs clog like you won't believe and often take 3 times to get right or give up on.

 

[TequilaSqueela]

We're in an identical spot with our 79 cb750k bikes.

Same behavior. Same checks. I have significant air leaks before and after the carbs so I have eight new insulators. Also need to check clearances.

 

[amc49]

X2, the intake manifolds cook to be hard as rock, you yank carbs and they then crack to vacuum leak. Common issue. Why they won't idle right or hang high at idle.