Fuel leaking from overflow tube.

[settles]

I have had a persistent fuel leak that I have been trying fix on my bike.  I replaced the fuel line from the petcock to the inlet on the carbs and put some clamps on the ends of the line.  That fixed the small leak.  

I took it out for a ride and ran great.  It did have a little hesitation above 5500rpms though. When I got home I discovered another fuel leak.  This one is leaking from the overflow line on the #2 carb.  I'm guessing the float is stuck.  It wasn't doing this when I put it away for the winter.  I am going to run some sea-foam in the gas just because I think it could probably use it anyway and maybe this will help.

I'm also going to try tapping on the fuel bowl with a hammer handle or something similar. Should I run the carbs dry when I do this?  Should I have the bike running with the carbs under demand?  How hard should I tap on it?

If I need to remove the fuel bowl can I do that with the carb still on the bike? Is this going to require me to re-sync everything?  I don't think it would but I don't want to open a huge can of worms.

[LukeM]

Fuel leaking from the overflow is a common problem.  Try a search on the home page of our forum with the words "overflow tube" and see what you find.

As far as fixing it, most of the time it's caused by a sticky float pin, or a bad seal between the needle valve and its seat.  Checking that needle valve usually involves removing the carb bank.  Look for a little cut line in the neoprene end of the valve. Also, you can lap the seat portion with some cotton on a swab and a bit of cleaner.  I've read where some will run a VERY mild abrasive on the seat to get it clean, but you do this at your own risk.

You can tap the carb lightly with a rubber or nylon mallet to see if it will stop.  I would not recommend using a steel hammer near there, as sparks and gas fumes can be a volatile mix.   Sea-Foam is a wonderful thing, but I don't think it will help you much if you have something mechanically wrong with this carb.  It can clean, and maintain a level of clean, but it won't unstick a needle valve or float.

If you wish to remove the carb bowl on #2, you'll have some trouble getting the bowl screws out.  Again, it may be easier to remove the whole bank and check it that way.

There is no need to re-sync the carbs if you're just checking the bowls.  You'll need to re-sync if you've changed the throttle screws/nut settings on the throttle mechanism.  It won't hurt to check them once a year or so.  Some guys do it once a month, but I find that a bit more AR than necessary. Carbs may tend to drift a bit over time, but the change may be so slight as one wouldn't notice.  Check it once a year.

I hope this helps. If you're new, welcome, and keep us in the loop.
Luke M

[settles]

Cool, Man.  Thanks for the tips.  I was going to use a handle from a broken ball-peen hammer to do the tapping.  I am not the most mechanically savvy dude on my block. I've fixed a carburator before but it was nowhere near as complicated as these.  I don't want to learn how to do it on my daily rider and scrwe it up in the process.  If it was on a stand in the re-build process that would be a different story.

So, if it involves taking the carb bank off I think I'm going to pay someone (who warranties their work) to fix it.  That way it gets done right and if it doesn't; it's getting done right the second time.  

I really didn't want to work on the carbs just yet since I plan on putting a sweet 4to1 exhaust and some race-carbs next winter. I just want the damned thing to stop spilling that precious $4.35/gal nectar! LOL!

Thanks again!

[Buster]

the overflow line connects to the bottom of the fuel bowl;  on the inside of the fuel bowl the fitting that the overflow line connects to, continues for another inch or so.  I had a hairline crack in the continued part.  It caused mine to leak steadily from the overflow tubes.

[settles]

I ended up just biting the bullet and taking it to the Honda shop.  I'm in the middle of moving right not and just don't have time to monkey around with it.  $400 later though =(

On Thu, May 3, 2012 at 2:41 PM, Buster [via Honda CB750'S] <[hidden email]> wrote:

the overflow line connects to the bottom of the fuel bowl;  on the inside of the fuel bowl the fitting that the overflow line connects to, continues for another inch or so.  I had a hairline crack in the continued part.  It caused mine to leak steadily from the overflow tubes.

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[Lucky 1]

Please be careful if you want someone else to do it.
Many dealers know NOTHING about these bikes. Big mistake as far as I am concerned.


You would be better off having a friend help you or watching videos on line or something.
IF it was mine I would order 4 brand new float needles. period.

BTW...You did not even tell us the year of the motorcycle or if it is a 750 or 550.

$400.00 !!!!! WOW.  I knew it. You could of had a CB750 expert rebuild your carbs for $270.

[settles]

I checked around. The guy at the Honda shop here has been there since '75 and owns two old CBs. Plus he warranties his work. 

Sent from my iPhone

On May 3, 2012, at 5:05 PM, "Lucky 1 [via Honda CB750'S]" <[hidden email]> wrote:

Please be careful if you want someone else to do it. Many dealers know NOTHING about these bikes.

You would be better off having a friend help you or watching videos on line or something.
IF it was mine I would order 4 brand new float needles. period.

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[Lucky 1]

That is a common problem reported on this site and SOHC forum.
It is from water freezing in the float bowl.

Just replace that float bowl.

We sure would like to see a photo of that $400.00 carb rebuild from a dealer.

I wonder if they farmed that out?

[Lucky 1]

Well you were lucky to have found the right person. Very good.

[settles]

I had him tie up a bunch of loose ends too.  Wasn't just carb work. 

Sent from my iPhone

On May 3, 2012, at 5:13 PM, "Lucky 1 [via Honda CB750'S]" <[hidden email]> wrote:

Well you were lucky to have found the right person. Very good.

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[Thorby]

Lucky 1 wrote

Please be careful if you want someone else to do it.
Many dealers know NOTHING about these bikes. Big mistake as far as I am concerned.


You would be better off having a friend help you or watching videos on line or something.
IF it was mine I would order 4 brand new float needles. period.

BTW...You did not even tell us the year of the motorcycle or if it is a 750 or 550.

$400.00 !!!!! WOW.  I knew it. You could of had a CB750 expert rebuild your carbs for $270.

My thoughts exactly.  I know my old bike needs carbs maintenance and my floats don't seem to work either but I can't bear the thought of some random dimwit mechanic messing with my bike.  They offer to do it for around $110 dollars here but it's an entirely different market with low wages.

Maybe I should get a buddy, find a video and go for it.

[settles]

He rebuilt all four carbs, flow tested them and synced them. Plus a bunch of other odds and ends crap. 

Sent from my iPhone

On May 4, 2012, at 11:15 AM, "Thorby [via Honda CB750'S]" <[hidden email]> wrote:

Lucky 1 wrote

Please be careful if you want someone else to do it.
Many dealers know NOTHING about these bikes. Big mistake as far as I am concerned.


You would be better off having a friend help you or watching videos on line or something.
IF it was mine I would order 4 brand new float needles. period.

BTW...You did not even tell us the year of the motorcycle or if it is a 750 or 550.

$400.00 !!!!! WOW.  I knew it. You could of had a CB750 expert rebuild your carbs for $270.

My thoughts exactly.  I know my old bike needs carbs maintenance and my floats don't seem to work either but I can't bear the thought of some random dimwit mechanic messing with my bike.  They offer to do it for around $110 dollars here but it's an entirely different market with low wages.

Maybe I should get a buddy, find a video and go for it.

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NAML

... [show rest of quote]

[Lucky 1]

"Flow tested them"  Flow tested what???  Sounds unlikely.

Why would you flow test stock carbs?

[settles]

Who said they were stock? It's a 35 year old motorcycle. I'm probably the 3rd or 4th owner. I have no idea if they are the original carbs. For all I know the guy I bought it from could've scavenged 4 different ones together. Probably not likely but if I'm paying to have them rebuilt I want to know that it's done right. But since you've never heard of bench-flow testing a set of carbs, it must not be possible. 

Sent from my iPhone

On May 4, 2012, at 8:53 PM, "Lucky 1 [via Honda CB750'S]" <[hidden email]> wrote:

"Flow tested them"  Flow tested what???  Sounds unlikely.

Why would you flow test stock carbs?

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NAML