Topic: 1978 honda cb750 ruuning problem

[drmeloh]

i finally got my bike running. i got some laps in and everything was fine until after a while my bike started to revv high automatically. i was told it might need the second return throttle  cable.
would this be the problem?!?

[BrockSamson]

I doubt that is causing your problem.  You should have one though for at least safety reasons.

I would check for air leaks at the rubbers that connect the carbs to the engine.  Spray some WD40 near the rubbers and if the RPM changes you have a leak.

[flybox1]

as your bike warms, you'll need to turn your idle down.
+1 on the air leaks, and probably not your return cable or spring.

ensure all carb boots, to engine and to airbox, are not cracked, are on correctly, and sealed tightly.

[drmeloh]

oh ok. i did rebuild the carbs, so the rubbers might be slightly off. i will check for leaks and right placement then. thanks!

[flybox1]

the boots should have a mark or tab on them which shows which side should be facing up.  its tough to see if they are on correctly, especially  in between 2 and 3, but do your best to get a finger in there to feel if any of the boot is pinched.  even a small mirror might help.  a small pinch or fold can cause a poor seal.  For ease of getting the boots on, leave your airbox disconnected from your frame while you are snugging the boots to the carbs.  when they are all on correctly and clamped tight, lift the airbox up to the mounting tabs. 

[drmeloh]

ok thanks man. i think i might be missing a clamp on a boot. so that might be one of the problems

[flybox1]

i think i might be missing a clamp on a boot. so that might be one of the problems

  uhhhh...YEAH!!! 

[MCRider]

Air leaks, poor routing, too tight adjustment, all usual suspects.

To be clear, the throttle should work and return perfectly to idle without coaxing or hesitation WITHOUT the "B" (return) cable. Once you have it working properly you can add back the B cable for safety sake. It should make no difference to a properly set up throttle. Its there as a failsafe, not as a part of a proper throttle.

[lucky]

i finally got my bike running. i got some laps in and everything was fine until after a while my bike started to revv high automatically. i was told it might need the second return throttle  cable.
would this be the problem?!?

Unfortunatly yes.... you have to have the return cable. The reason why is that with one pull cable on that 1978 carb set up, the throttle snaps back so fast that the cable can get loose on the quadrant and the barrel can get hung up and causes the idle to get hung up.

It could actually come off the quadrant but not likely BUT it is a possibility.

[flybox1]

To be clear, the throttle should work and return perfectly to idle without coaxing or hesitation WITHOUT the "B" (return) cable. Once you have it working properly you can add back the B cable for safety sake. It should make no difference to a properly set up throttle. Its there as a failsafe, not as a part of a proper throttle.

+1

It cannot come off if properly connected at the throttle sleeve bell, the carb throttle bell and locking brackets, and when tensioned correctly 

[bollingball]

as your bike warms, you'll need to turn your idle down.+1 on the air leaks, and probably not your return cable or spring.

ensure all carb boots, to engine and to airbox, are not cracked, are on correctly, and sealed tightly.

Fly I don't think you should ever have to do this once the 3K service is done.
 This is what the choke is for.
Ken

[flybox1]

I politely disagree.
after riding my bike to operating temp, and lowering my slides to an optimal idle, i cannot (even on my 350F) start my bike cold the next day, without using both the choke(closing butterflys) AND raising my slides with the idle set screw. (then my choke goes off and my idle set screw is adjusted back to good idle.
if you can, id like to know how you do it.

[xnoahx]

To flybox, maybe you need to adjust your fast idle speed on your carbs

[bollingball]

I politely disagree.
after riding my bike to operating temp, and lowering my slides to an optimal idle, i cannot (even on my 350F) start my bike cold the next day, without using both the choke(closing butterflys) AND raising my slides with the idle set screw. (then my choke goes off and my idle set screw is adjusted back to good idle.
if you can, id like to know how you do it.

There is no need to do that on a 78 750K That is why you have a fast idle cam. The way it works is like this. On first start in the morning when you pull your choke all the way it will automatically raise your slide That is why you have a cold idle 2750 + or - 750rpm Look at page 313 in the manual section 3 part 9 When you start to push or open the choke it will come off this cam and go back to normal idle speed. once you get this setup you will love it. I missed at first to.


Ken

[flybox1]

I will be trying this in the am