'81 cb650c , all four carbs overflow out the throats

If it's broken or just needs tweaked

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adamb
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'81 cb650c , all four carbs overflow out the throats

Postby adamb » Sat Jan 02, 2010 9:44 pm

I have a 1981 Honda CB650C that I picked up for a song. I have thoroughly cleaned the carburators, and they are extremely clean at this point.

However, since putting them back together, they overflow. Not out of the drain at the bottom of the carbs, out of the intake hole (the throat?).

There is one thing that might be changing things though - the vacuum "tee" hoses that connect carbs 1&2 and carbs 3&4 were excessively rotted, and so I have simply used a small rubber hose to connect the two carbs instead of teeing them to the single line that goes back to the airbox.

Testing I've done: The float valves work. If I take the bowls off, send gasoline to the carburators, and lift the floats by hand, the gas shuts off to the floats I have lifted. If I turn the carbs upside-down, and apply gas (from high above the carbs), no gas flows into where the bowls would be. If I lift the floats slightly, gas starts bubbling into the carburator. It does not appear that the float valve seats are pitted or filled with junk. The float valve dealies look just fine. There is no way to adjust the float height - the floats are 100% plastic, and there's no way to try to adjust the float valve to adjust the float height.

I have first, this question: The diaphragm above the carburators shuts off the flow of gasoline to the carburators unless the engine is turning over. So, do the little vacuum tees somehow limit the flow of gasoline to the carburators when the engine is running? So, if there's a vacuum to the vacuum tube to the gas diaphragm thingy, maybe the vacuum from the airbox to those little tees on that connect to the carbs provides a way for the carbs to additionally shut off, or request less gasoline?

The only bit I'm missing is whether or not those vacuum "tee"s actually help hold back the flow of gas, or something. Unless the floats are sticking once I put the carb bowls on, there's no other reason I can find that would cause all four carbs to overflow out their throats when gas is flowing to the carbs.

My next test, when I can, is to take those joining tubes off of carbs 1 and 2, and see what happens when I let gas into the carbs. SEcond, is to connect one of the carbs with a tube, and apply a gentle vacuum when I deliver gas to the carbs... Unless you guys have a solution for me

cb650
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Re: '81 cb650c , all four carbs overflow out the throats

Postby cb650 » Sun Jan 03, 2010 11:16 am

You probly do need the "t's". They loop up so might hold some fuel. But you shouldnt have fuel coming out of the throats. All the floats check out good? All it would take is one bad one or a bad needle.
Did you clean the tank out?!?!?!?!

adamb
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Re: '81 cb650c , all four carbs overflow out the throats

Postby adamb » Sun Jan 03, 2010 1:11 pm

Last night, I disconnected those tees, and when the carbs overflowed, gas poured out them. Bummer.

I took the carb bottoms off, checked again, put them back on, gave them a few good whacks with a board, and ran gas through them... no overflow, this time. I'm going to try a few hardware stores to see if I can avoid spending $90 for the "tee" assemblies, which is the only way I can buy them (each assy is about $45).

I might just try to run each carb to the airbox, and then three-way-tee them to the other three way tee, which would do the same thing with twice the hose.

Last night when I *did* get the carbs on and they didn't leak, the bike ran veeeeery well.

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Volker_P
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Re: '81 cb650c , all four carbs overflow out the throats

Postby Volker_P » Tue Jan 05, 2010 2:44 am

Welcome here! :D
I don't have experience with CV carbs (and consequently the tees), but I think the carb bowls should not overflow even without them. The floater cams need to be quite perfectly straight and smooth. As you managed to solve this with a bit knocking there is some chance that the floaters run in with time. Worked for my dirtbike some time ago, so worth a try before further opening.
If you find a solution for the tees I think many here would be interested so please report and take some pictures if possible.
The shutoff valve has no further limiting or regulation function and may be removed as soon as it causes trouble (or better even before :wink:). But plug the vacuum connection.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

adamb
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Re: '81 cb650c , all four carbs overflow out the throats

Postby adamb » Wed Jan 06, 2010 12:59 am

I know for sure that the float valves are ok, and that the seats and so forth are working fine.

Originally, I had carbs 1 & 2 , and 3 & 4 directly linked - bad idea. Overflow-o-rama. Removing that link helped a lot, but they still leaked. I need those tees. :(

I thought up two solutions for my tee problem:
1. Two rubber stoppers, with a hole drilled lengthwise to mate the two carbs, and one perpendicular to that first hole, to link back to the airbox.

2. A plastic/nylon vacuum tee whose inner diameter was roughly the same as the outer diameter of some vacuum/gas line that would fit over the nubs on the carbs. Trim the tee arms to fit between the carbs, and squeeze the hose into the tee. Run the final end of the tee to the airbox.

Ok, one more:

3. Get a large enough rubber vacuum tee at an automotive shop that I can trim to fit.


#3 seems impossible, as I can't find a tee large enough (In alaska, automotive shops aren't the biggest, and ordering is a pain)

#2 seems ok, but there's no true way to make absolutely sure there's no leak, or that none of the connections will wiggle loose.

#1 is the most hackish, but also remarkably cheap - $1.67 for a rubber stopper, and about $2 apiece for a brass tee (I realized too late that I could just yank the metal one out of the old rubber tees, but those were also slightly smaller and less barbed)

It works... ok. It's probably about as secure and trustworthy as those silly rubber tees from Honda, that's for sure, and since I cut the rubber stoppers "too long", the carbs squish them together nicely. I don't know how it'll hold up with heat and vibration, but I'll be testing that as soon as I can.

Here are pictures of the 'final product', so to speak - they aren't good, but then, I wasn't about to take them back apart so I could get a better photo:

1. http://picasaweb.google.com/adambultman ... 7126556642
2. http://picasaweb.google.com/adambultman ... 5172753650

Those interested in my progress thus far can see my whole mess of photos here:
http://picasaweb.google.com/adambultman ... 50Cleanup#

I'm basically finished with the carbs now; I bought some high-temp gas line and ran it on the carbs, there's a kink in the connection from the fuel valve to the main tube to the carb bodies, but I cant' find gas line stiff enough NOT to kink.

I also bought vacuum lines to replace the old, rotting ones, which will make it look nicer.

I'd have put the carburetors on tonight, but I've been cleaning out the airbox, and I have to install THAT first - so it might have to wait for tomorrow night, or Saturday.

I also tested the compression - 130, 115,108,105 for cyls 1,2,3, and 4 respectively - which is probably OK. I was told "around 110" was fine for my bike.

Once I put on the carbs, and let it run for a bit, I'll give it a bath and see if I can't get rid of all the grime.

cb650
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Re: '81 cb650c , all four carbs overflow out the throats

Postby cb650 » Wed Jan 06, 2010 8:45 am

Good post. Thought something like that would work. Good carb pics on you web album too.
Did you clean the tank out?!?!?!?!

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Volker_P
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Re: '81 cb650c , all four carbs overflow out the throats

Postby Volker_P » Thu Jan 07, 2010 1:57 am

Yes, many nice CV carb pics. Maybe still helpful for explaining things later. If knocking on the carb bowls stopped leaking (that's my understanding), your floats don't move that freely as they should. If you really put all cleaned parts together in one box and then started to build up four carbs from that, it would be no real surprise that the floats stick a bit at the beginning. If possible, better avoid mixing old moveable parts with a bit wear between carbs.
Differences in compression between cylinders are considerable, nevertheless with these values it still should run fine. Possibly it will smoke a bit on 3&4 beyond 6000rpm, keep an eye on your oil level until you know how much it consumes.
For the gas line, one could use a harder one and bend a bow at heating it. Or leave it long enough for a loop. Keep that in mind in case you get hesitations at higher rpms after a while. Additional flow restriction may also be caused by a partly plugged filter screen in the tank at the fuel cock.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

adamb
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Joined: Sat Jan 02, 2010 9:29 pm

Re: '81 cb650c , all four carbs overflow out the throats

Postby adamb » Thu Jan 07, 2010 2:12 am

The knocking on the bowls may be a red herring. I knocked on the bowls with wood *after* I had also taken the tubes off that connect the carburators.

As for my pile of parts - the floats did get kind of intermixed, but they all "float" and move freely. Due to staining (sigh) I was able to fairly easily figure out what parts went to what carb.

I put my airbox in yesterday, and connected some of the hoses tonight. Tomorrow, my carbs go on, and I connect my fashioned carb 'tees' to the airbox, and fire it up! Once it is warm, I'll do another compression test to see what happens.

adamb
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Re: '81 cb650c , all four carbs overflow out the throats

Postby adamb » Fri Jan 08, 2010 1:09 am

I got my carbs back on the bike tonight, and it runs, and no overflowing! I forgot to sync up the throttle plate on the #4 carb, so I have to operate it manually apart from the throttle - but I also don't have the airbox to carb rubber "connectors" on right, so it doesn't fit in there properly. As a result of the throttle plate, the bike sounds like it has a cam in it or something.

So, once I fix those two things, and tweak my idle mixture screw, I should be back up and running properly - and I'll be able to move on to the next portion of this fixer-upper.

Thanks for all your help, but stay tuned, there'll be more!

adamb
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Re: '81 cb650c , all four carbs overflow out the throats

Postby adamb » Sun Jan 10, 2010 12:49 am

Carbs back on, here's some video of it, and how it sounds:

http://www.youtube.com/watch?v=E6LJ7WkSBcg

Here's a second video, but this mostly me talking to myself about some other things I found:

http://www.youtube.com/watch?v=TxBFOGdri3A

On the plus side, when it was warmed up compression showed about 130 PSI per cylinder.

On the down side, I can't figure out how the heck to get the carbs on with the airbox. I cleaned out the airbox, which included taking off the airbox to carb intake connectors, and I can't figure out how to get them on properly. When I try to install the carbs, it knocks those off the airbox, and when I do actually get them on, they aren't tweaked right, because they don't all match up very well. I'll figure it out soon enough, I suppose, but if you have tips, I'd love to hear them.

cb650
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Re: '81 cb650c , all four carbs overflow out the throats

Postby cb650 » Sun Jan 10, 2010 5:08 am

couple posts on sohc4 for you.
Did you clean the tank out?!?!?!?!

Rocky
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Re: '81 cb650c , all four carbs overflow out the throats

Postby Rocky » Sun Jan 10, 2010 8:54 pm

cool videos. the bike sounds good.

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Volker_P
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Re: '81 cb650c , all four carbs overflow out the throats

Postby Volker_P » Tue Jan 12, 2010 3:09 am

Have a closer look at the airbox to carbs rubber boots. They are slightly excentric and by turning them you can make them line up wit the carb intakes. :wink:
Maybe they have even marks for the correct top orientation.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

adamb
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Re: '81 cb650c , all four carbs overflow out the throats

Postby adamb » Tue Jan 12, 2010 2:18 pm

The only marks are the marks left on the boots from when they were made.

Lining them up is almost impossible; you can't rotate them while they are on the bike (the amount of space I have to work with could be measured in millimeters) and removing the carbs and putting them back on inevitably knocks the boots off the airbox - which means I have to start over. And, my hards are rather large, so even if I *did* manage to squeeze that airbox back enough, I still wouldn't be able to do much because of the size of my mitts.

Right now, they are on there, they are all clamped down, and as far as I can tell, there's no air leaks.

I couldn't think of a non-permanent glue that would help those boots stick on (I put a little silicone in the joint there, but silicone dissolves in gasoline), but even if I *did* know of one, I wouldn't put it on until I have to do some other major thing to the bike.

cbonne
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Re: '81 cb650c , all four carbs overflow out the throats

Postby cbonne » Tue Sep 14, 2010 7:17 pm

Just wondering how your makeshift tees are holding out I've got to do the same thing to mine and 40$ each is not really appealing


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