Topic: 1976 CB550F Leaking gas out of the carbs and into the airbox, why???

[TwoTired]

So, you are telling me my floats are upside down in all 5 sets of spares?

What flats are you talking about?  Are you envisioning the PD carb floats?

[harisuluv]

Those are oriented right.

[Bodi]

"So, you are telling me my floats are upside down in all 5 sets of spares?"
No, I was asking. Keep your panties on. You're saying you checked five sets of spares? Wow.

[marty]

Wow, lucky you! I wish I had just 1 spare set so I could put it on and see if the bike runs great! Which it should!
I'm back to the drawing board, I've got the carbs back on the bike. I'm going to try and make one of those float bowl plug screws with the tube coming out of it so I can check how much gas is in each carb with the petcock on. If that looks ok, I've made a short brass float measuring tool, cut out to 22mm, that way I can more easily check the float height with the carbs on the bike.

[marty]

Thanks for clearing up the fact that my floats are in correctly.

[Doctorlumen]

Hey Marty,

Not to beat an already beaten dead horse, but is your bike on the center or side stand when the carbs leak? My 400f drains gas out of the tubes when I start it up after its been sitting for a while (like several days). On a whim, I stopped parking the bike on its side stand. No leaky. I have the crumby Keyster float valves, which don't help, but maybe the center stand thing will.

Also, you mentioned that the carbs drained into the airbox before you got into them right? I'd wager you wouldn't be the first kid on the block to sort out and fix something the previous owner F-ed up for you. I would as a matter of course grab my shop manual and a beer and completely strip those bad boys off their rack, clean the hell out of them, and assemble paying special attention to the manual and not what was there before. I mean, carbs can't be "too clean" after all. And maybe there is more going on than you can see with merely the float bowls removed.

[marty]

It seems that may be the case. I heard from the local vintage honda shop that it's pretty tricky to reassemble all 4 carbs if you've never done it before. (which I haven't) getting them apart will probably be easy, but I can see how it would be tricky to get them back together properly. I generally find it's best to do things like that all in one swoop, that way it's fresh in my brain; how it all came apart. I usually take photos to help document the process.

The bike leaks on it's center stand. Straight out the back of the carbs and into the airbox, then it drains out of the airbox in a steady stream onto the ground. I don't have a hose connected to the airbox, so I just watch it stream straight out. Not a pleasant sight, especially after putting the carbs back on for the third time. I fired up the bike with the rubber boots off, so I could see the back of the carbs, no leaks. Then I put the boots back on, fired it up again and it starts leaking! The bike did sit for a long time, so maybe there's something deeper to be dealt with. you are correct, they can't be too clean!

[marty]

Finally, some relief! Unfortunately, it was a mystery fix.

I went down to the garage yesterday, determined to sort out this leaking carb issue. Pulled off float bowl #1 with the carbs on the bike. It had half the amount of fuel it should have, this is after it sat for a few days. I checked the float height and turned on the petcock, holding the float at 22mm, no gas made it past the float needle. In addition, no gas was coming out of the airbox, which usually happens when I turn on the petcock.

I then went to carb #4 and it had twice the amount of fuel #1 had. I performed the same test, still no leaking. "Well this is a first, the bike is acting like it should" I put the float bowl back on and turned on the gas. No leak. I wheeled the bike out of the garage, full choke, started right up. Still not leaking. Let it run at 3K rpm for a few minutes before dropping the choke fully. Still no leak! Let it warm up for another few minutes, the bike idled nicely around 1,200K.

I took it up and down the block, ran well, no leaks. Put it on it's side stand, still didn't leak. I then got bold and took it out for a 10 mile ride, made sure it was up hill, so i could coast home if need be. It made the trip and ran well, idled smoothy. I turned the bike off 3 or 4 times, just to see if anything would change after re starting it. It acted like a normal 550 should act.

I'm going to run some techron carb cleaner through it, since the only solution I can come up with, is that some of the carb cleaner I was using finally dissolved something that was in the carbs. It's hard to trust a bike that was leaking gas and running poorly, then after a few days it runs great. Especially when I didn't change anything, I was just checking the float heights.

[marty]

I just did another 15 miles. After 5 miles, I stopped with the bike warmed up and reconnected the drain tubes at the base of the float bowls. I heard the idle drop below 1K then the bike shut off and started leaking gas out of the airbox again. I disconnected the drain tubes and it started up and ran fine. The drain tubes were plugged up with dirt, but I didn't think that would affect the carburetors. apparently it does. I put new drain tubes on and it rode just fine, didn't leak any gas.

I don't think the "on" position on the petcock is working. With a full tank of gas it runs in the reserve position, but in the on position after a minute or two the bike is starved for gas and shuts off.

[TwoTired]

The drain tubes were plugged up with dirt, but I didn't think that would affect the carburetors. apparently it does.

Too Funny...

I did mention to check those drain tubes in reply #8.

Some people just have to learn the hard way, I guess. 

Guess you don't have to worry about reliability, anymore.

[Doctorlumen]

Glad you got it sorted Marty! Got to say though, weird that a clogged drain hose caused such a problem. You might still consider pulling the carbs and doing a full clean. For the record, if you have the presence of mind to check and re-check your floats at 22mm and/or build a tool to measure said floats, you can have your carbs completely apart, cleaned, and back on the bike in a albeit long afternoon. Be focused, organized and confidant. There is nothing you can't do.

[fastbroshi]

I don't think the "on" position on the petcock is working. With a full tank of gas it runs in the reserve position, but in the on position after a minute or two the bike is starved for gas and shuts off.

Care to post a pic of the tube that leaves the petcock and feeds the carbs?

[marty]

true two tired, you did mentioned the drain tubes could be blocked: However, i think I was distracted by your comments on my problem defying physics; I neglected to retain the key element in your response. haha We live and learn.

"If the carbs are level, the fuel must drain from the tubes before spilling out the air jet.  Unless ... the carbs aren't level, rudimentary physics don't apply where you live, or the overflow tubing is blocked.

Can you make the liquids only occupy the right side in glass container?

I can't help when given false information.

Sorry,"

[birdmannn101]

Marty, I stumbled on this old tread of yours because my Hondamatic 750 is leaking gas into the airbox too after cleaning and setting the float height.  I have all new  overflow tubes on my carbs and it still leaks in to the air box.  I know you said that a dirty tube caused your problem and I am happy for you.  If it didn't and you eventually fix the problem again I will be waiting in the wings for your answer.

[stewonepot]

Try the "open to atmosphere" tubes
Regards Stew