Topic: 79 CB650 carburetors

[DaveBarbier]

Where do they drain out of? Why is it that fuel drains out but when you connect a clear tube it doesn’t? That doesn’t make sense to me.

[CBR954AD]

see my old post from last year. ill try it again today and take good pictures and video.
where are the 2 tubes supposed to go? i have air pods no box. At moment there is nothing connected to them

[DaveBarbier]

Those I believe are just vent tubes and aren’t connected to anything. Normally they route behind the air box. Not connected to the air box, just behind it somewhere. 

Make sure they aren’t clogged either. The carb needs to vent to atmosphere to allow fuel to feed the carbs.

[CBR954AD]

Ok clear tube test done. See images. Carb 4 is way under float bowl seal, 3 is close.carb one is above ,and 2 is way above. Another thing happened when I pointed the tube down to drain carbs 1,2 not only did the fuel seen in tube came out but also way more after that. Kept flowing for about 15sec per carb. On carb 3 and 4 only fuel in clear tube drained nothing else.
Also book says accelerator pump rod need a .05mm to .06mm gap. Mine is flush touching .
The brass tube on inside of float bowl, I believe is the overflow , I can run wire through it and blow air on all 4.
https://photos.app.goo.gl/AhpFHJgeew3pPe5x9
https://photos.app.goo.gl/VcCAq8MLn2Xr8KaT9
https://photos.app.goo.gl/deLVcvyf5R9mToXcA
https://photos.app.goo.gl/NCbgE7Mwsyqwqbrr6
ttps://photos.app.goo.gl/g29i8UTcgYvqEzNX8
https://photos.app.goo.gl/N5c1FE2uKCx3nSTr5
https://photos.app.goo.gl/eQJv392UgNq5JHrC6

[CBR954AD]

So I fixed gap on the accelerator pump rod,.
Now why do 1 and 2 leak? I have checked several times by blowing air into fuel line and manually closing and opening bowl. The needle does seal air. Why did both carbs have so much fuel when I did the clear tube test? I did not have fuel tanki filed carbs then connected a 100ml bottle to fuel line to run bike and test. When I did clear tube test the auxiliary fuel can was just about empty had maybe 10ml and what is left i 10in long line to carburator s

[DaveBarbier]

1 and 2 leak because the floats are set too high.

These are good results and good pictures. It’ll take some fiddling, but adjust the float height so the fuel level is about 4mm below the bowl seam.

And for some reason I can’t see all your pictures. Some come up blank. You might want to try uploading directly to the site or if they’re too big maybe try uploading to imgur.com and then paste a link?

[CBR954AD]

I'll try adjusting one and 2. I can't upload pictures to we site because file to large it tells me, even for one image in low image quality

[CBR954AD]

Can you see all 4 clear tube test pic? Other 2 are of the brass tube inside the bowl

[CBR954AD]

Can't remember do I open the tab or push in tab to adjust float

[Nicklopic]

there is a 4MB limit for attachments.
if you use you phone when posting, I just found a simple app called lit photo. its a file compressor. you can select multiple images and compress the file size to what you want.

Once you open the bowls you should see how the tab is supposed to be bent to do what you need. I was told to make sure float height is set with barely any pressure on the needle so do not set them upside down. I kept them at a slight angle from horizontal so it applied very light pressure.

[CBR954AD]

Got it. Yes I use my phone.
I have another question. Does this engine have a crankcase breather?

[Nicklopic]

yes, it sits on the top of the middle rocker cover. its just a nipple. from the factory it ran back into the air box. you can put a breather filter on it if you like or run a hose down and away from things.

[CBR954AD]

So what is this relief valve by oil pump see image number 5
https://photos.app.goo.gl/o7QULtNQKbSds5Hz6

[Nicklopic]

the diagram does not load for me. If you could post a screenshot that would be sweet.

[CBR954AD]

It's ok. Can't load pic.

[Nicklopic]

my motor is apart on my bench currently with the side cover off. ill look at it when I get home but I don't remember there being any vent over there

[CBR954AD]

This is part number from Honda
Honda VALVE, RELIEF Part # 15140-300-010
What is the function of it?
Thank you

[DaveBarbier]

That pressure relief valve has nothing to do with your carbs. That controls the oil pressure going through the engine.

And Nick, the act of angling the carbs to set float height is only when you’re trying to hit a specific number. In the OP’s case he just needs to bend the the float tang up or down to get the fuel level correct. This can be done with the carbs installed. But you’re right that holding he carbs upside down will compress the plunger in the float needle throwing results.

[CBR954AD]

I was just asking what this relief valve job or function is. I know it has nothing to do w carbs. It has to do w oil system but exactly what. Thank you. I will try to get to the carbs tonight make adjustments and try clear tube test again. If it's good I will run set idle, and synchro nize the carbs

[CBR954AD]

hey guys would this exhaust fit my cb650?
i have to take my bike to Washington state patrol for inspection to get my title. when i bought the bike it came in boxes. lol
https://delkevic.com/full-system-to-fit-cb750k-sohc-1977-1978-with-classic-straight-universal-muffler-and-stainless-steel-4-1-headers/

[DaveBarbier]

Highly doubt it. I’m sure it would take some heavy modification.

[CBR954AD]

https://photos.app.goo.gl/BERX3Mu4MXjWrGZE9
Watch video. I'm using 10 psi shop air. Carburetors are leaned back so all float and needles are closed no air or fuel should be coming out. You can hear air hissing from 1 and little in 2. 3 and 4 are solid nothing. Even if I push the needle by finger air still hisses.  Same test on 3 and 4 and no air. . I also just received my oem Honda carb rebuild kit so all parts top notch
 I paid 35 per carb for kit.
Ok
I just tried something.
I swapped float and needles from carb 4 the good one to carb one. And put fuel. Still carb one is leaking and carb 4 is not.
This confirms issue is not in float needle setup but in carb somewhere else.

[CBR954AD]

Here is clear tube test pictures after swapping float needle set from 4 to 1.
https://photos.app.goo.gl/1rnWPMYsT1cTtEgu6
https://photos.app.goo.gl/LNvYafxCdk999ciT9
https://photos.app.goo.gl/XmFmiYEHenFDUYGu7
https://photos.app.goo.gl/9EH8QHYmW5jx85S6A
As you can see carb 4 with float set from 1 ,fuel level is on the money. But carb 1 with float set from 4 which is a good level when installed on carb 4 is way up high again. As you can see carb 2 is good now and not leaking.
Any thoughts?

[scunny]

are the float needles all the same type and same length.
they are rubber (viton ?) tipped in my 79 pd carbs.

[DaveBarbier]

I can’t view the video. It says “video will be ready soon”.

Glad you’re getting an OEM rebuild kit but really, float height with the clear tube method should be done first to get fuel level all correct, and then see if issues arise. What comes in the rebuild kit?

For your pictures, unfortunately none of the fuel levels are good. Not even #4. Waaaayy too low. That’s not 4mm below the bowl seam. Make a cardboard template and use that.

Also, all your tubes are kinked at the overflow nipple and can be restricting fuel flow.

You need to connect the tube, hold it up to the bowl seam and keep it still, don’t move it around, and then open the drain screw.

Note the fuel level and note the smooth bend of the fuel line.


Here’s my PD carbs on my 550.