HondaCB650

I have a 1982 CB650 with the CV carb and head setup. I have hardtailed the bike and removed the old airbox. Unfortunately, I cant get the damn thing to run correctly even after getting the carbs cleaned and synced. It will run fine for 15 minutes and then idle high. I have checked for air leaks around the boots and all that. Nada. So, I'm thinking about going to mechanical carbs from a CB750. Anyone know of a set that could possibly match up with minimal modification? If anyone has other tips they would be greatly appreciated.

My 79 has mechanical carbs. Start looking in that direction. The problem is most likely your filter. It's too open, and not allowing enough suction for the diagrams to work. My guess.

You could try to build a shield around the filter with a small gap.
Cycle exchange has half-round shields on their pod filters.




Something as simple as cardboard will get you an easy way to see if that's your problem.

I have a set of '78 cb750 mechanical carbs that are identical to my 650 so that might be a place to start as well.

Welcome here!

Nice project!
Be happy you have the CV carbs. Things usually get more difficult with piston carbs! They are significantly less forgiving with regard to jetting and open filters.

First check for air leaks, that's most probable.

Are all four header pipes equally hot?

If this should be all right: When it starts to idle high, turn out the manual idle knob. If it looses contact and the idle is still too high, your synchronization is poor. Make sure all four throttle flaps open and close simultaneously to the same small gap at idle.
This visual synchronization should be sufficient, vacuum synchronization only works if verything else is really all right! Maybe you tried that with a small air leak.

Another option might be the lobe of the choke cam. There is a screw for adjustment, the throttle should be lifted slighly only when the choke is fully engaged. However I'm not sure if this exists for the CV carbs, too

Jay, I notice that in your picture that you still have your automatic petcock still installed. Mine is missing. Could this be a reason for a high revs? I also made a slight description error. The bike runs fine untill on the clutch or in neutral. It revs high but once load is applied to the motor, it returns to normal.

Sorry, those pics I stole from cycle exchange's website. I'm running non-cv carbs on my bike.

As for reving high without load, I'd guess that it might be running rich. Kinda like you've got the choke on. One way to check is to pull a plug and see how it looks.
Spark plug check

And have you cleaned it, could be a clogged jet. Improper air mixture could also cause it as well.

Good luck and tell us how it goes.

So what ever did it turn out to be? These threads are useless unless you follow up on them

Sadly, only Volker_P has been here since this thread was made in 2012.

Folsoml wrote:Sadly, only Volker_P has been here since this thread was made in 2012.

Yeah well they still might get the email notification .
These threads could be gold to people had their authors completed their stories. Or at least respond when asked. *Wink wink*. I try to close all mine so others can learn from them especially since I'm getting free help from those willing to donate their time to help. Least I can do is spread the gift to those following along