Topic: 79 CB650 carburetor Help

[CBR954AD]

Hey everyone,
Looking for some assistance in fixing my stock carburetor. They are of 79 cb650 Keihin carbs . I bought a complete rebuild kit and gasket kit from hohome so all parts are OEM.
Here is the problem. Once I turn fuel on from petcock carbs fill up, I start motor.
After 1 min carb 1 and 2 start leaking from float bowl drain/overflow on bottom. 3 and 4 are fine. I have set float height to spec by book on all 4, and have all new parts even floats and needle.
Today I devoted to swap float from the non leaking carb 4 to carb 1. Start motor and again 1 start leaking. This tells me that float height is not issue. Something else is causing fuel to overflow.
If any carb gurus on here please assist me. I have been battling these carbs for 3 months.

[riverfever]

You say you set the float heights but have you verified where the fuel level is in each bowl? If you search for "clear tube method" you should find some information on this.

[CBR954AD]

No I have not verified fuel level in each one.

[scunny]

+1 on the clear tube, it tells you what's going on inside. another thing to look at, the overflow(standing pipe) which comes out of the same orifice could be split, have a look at that.

[CBR954AD]

i am going to perform the clear tube test today, after reading on it, it will tell me how much fuel is in the float and  if the carbs have same quantity. i did not think about a crack on the overflow standing pipe . i cant think of anything else, since i swapped floats from a good carb to #1 and still started to drain/leak. most reply on the clear tube method say the level should be about 3mm below the float bowl gasket.

[b52bombardier1]

My rebuilt carbs initially had aftermarket float valves that to begin with did not leak but after a few weeks, leaked badly. So upon the advice of many knowledgeable folks around here, I bought OEM Honda float valve assemblies and that solved my problem.

Yes, at 32 bucks each, it's expensive for a set of four. But I was really getting fed up with taking those carbs off and back on. It's all good now though I do still have a minor leak if I leave the bike on the side stand. Resting on the center stand, no problem.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

[CBR954AD]

All components and gaskets RE oem honda.
I'm little confused about clear tube method.
So my carbs are on bench I have the mounted as they are on bike. I have a clear tube connect on drain nipple and drIn screw open. How much fuel to pour?
Thank y

[riverfever]

Pictures are worth a thousand words but I'm afraid you're not doing it properly. What I did was take a drain screw and drill it out and then I epoxied a brass tube that went through the drain screw and stuck out maybe half an inch. This is where I slid the clear tube on. Then you're going to hold that clear tube up against the side of the carb bowl, open up the petcock and let the carbs fill up and then look and see where the fuel level in the tube lines up with the bowl. Then you'll know if the level inside is truly 3mm below the gasket or not and then begin the process of shutting off the fuel flow, draining that bowl, removing the bowl, removing the float, making a very minor adjustment (one way or the other), reinstalling everything and repeating until you get the result you want.

[CBR954AD]

 So I don't understand why you need to have a tube plugged into to the drain screw
 Why can't I just fasten the tube onto little nipple on bottom of the float bowl. I reD few write up, and I seen pictures of just the clear tube hooked up to the float bowl drain.
When do you stop pouring fuel into carb? If you leave petcock open it will keep filling the tube correct? It's called pressure differential

[CBR954AD]

Here is image, why won't this work. And just open the drain screw? Or am I supposed leave drain closed and fill till carb overflows?.
Thank you for all help

[riverfever]

I don't know much about 650 carbs. I think I recall reading somewhere that PD series carbs can be clear tubed from the overflow tube but I have no clue if 650 carbs work the same way. When you attach the clear tube to the overflow tube and open the petcock, what do you get? Again, if 650 carbs operate the same way as 627B and O22A carbs then attaching a tube to the overflow, turning on the fuel and opening the drain screw will just result in fuel pissing all over the place. I can't explain the physics of it (great that it's called pressure differential) but I do not think that measuring from the overflow tube will produce the same results as the drain screw. You're talking about fuel maybe barely being too high (just high enough to enter the overflow tube) versus the drain screw telling you exactly where fuel levels are (both high and low and very accurately). Again...assuming 650 carbs are the same as 500 and early 550 carbs.

And when you have the clear tube hooked up (either overflow tube or drain screw whichever you decide to go with) you open up the petcock and let fuel flow. It will take a bit for the bowl to fill but don't turn it off. Measure your level against the side of the bowl. Once you're satisfied THEN shut the fuel off and do your adjustments or move on. Good luck.

[scunny]

you don't need to do that mod to the 650 carbs. fuel flow will stop when the float rises enough to close the valve. the clear tube you have will reflect the level inside the bowl.

[riverfever]

He doesn't have to do what mod scunny? Drill out the drain bolt? So then do the 650 carbs function like the PD's?

[CBR954AD]

riverfever, the drain and overflow are 1

[CBR954AD]

riverfever, the drain and overflow are 1 unit. it is the same thing. the image i posted above, you can see where i attached the tube to bottom of carb is where the fuel will drain if i open the drain screw, and also if carb overflow it will drain from same spot.

[riverfever]

My apologies 954. Were you able to come to any conclusions?

[CBR954AD]

yes, i found a crack on the overflow needle . i had a spare flow bowl, so i replace it and good now. however 32 is still leaking and no clue

[jgger]

Here is image, why won't this work. And just open the drain screw? Or am I supposed leave drain closed and fill till carb overflows?.
Thank you for all help

It would keep filling the tube IF you didn't have the floats and needle to close off the fuel flow. If it does run over on the tube then the float isn't floating or the needle isn't shutting off the fuel. Remember you're checking the float level to compare across all 4 carbs.

[RAFster122s]

You can sometimes clean and solder a cracked overflow tube, use plenty of flux after cleaning when soldering.