Fuel Leakage

[LODY]

I tried to get my dad's ole 1980 CB750K running after he had it sitting in his garage for the last year or so. I had bought it from him since he planned on either scrapping it or putting it out in the back pasture.  Anyway... I got a battery charged for it and put new fuel in it since the tank had been drained after the last time he ran it. It didn't seem like it was gettin fuel so i decided to loosten the bleeder screws on the bottom of the carbs. It took a bit, but fuel did slowly start to drip from the nipple. After the indication that there was fuel going into the carbs I decided to crank it over. It took a minute or so and all I got was a little bit of a pop when I quit turning it over.  I tried immediately again and smelled a strong gas odor. I quit turning it over and got off the bike just to see that the carbs were just leaking onto the block and the floor.  I turned the gas off and it quit obviously, but Why would it be doing that? I haven't had any issues like this with my smaller hondas, or even my sleds. What would ncause this?

[sgtslag]

It sounds like the carbs are gummed up.  They will need to be disassembled and cleaned thoroughly, especially the jets' tiny little holes which gas passes through, to be atomized.  There are video links to YouTube on the Home Page, that demonstrate how to do it.  The Factory Service Manual (FSM) is also available for download from a link on the Home Page.  After you get the carbs cleaned, adjusted, and synchronized, run some SeaFoam through the tank, to dissolve any varnish within it, as well as absorbing any water that may be lingering at the bottom of it.  Run some SeaFoam through the gas tank once per month, or so, to keep the carbs clean, and water at bay; used as a preventative measure, SeaFoam will prolong the life, and health, of your carbs, and the bike as a whole.

I'd recommend changing out the fork fluid, and the crankcase oil and filter, soon, as well.  The fork tubes use Dexron III ATF (around $5/quart, nearly everywhere), and changing it will make a nice improvement in the handling.  Cheers!

[LukeM]

Agreed on the need for cleaning the carbs, but make sure you have everything else: good compression, good ignition, clean oil in the case, well-charged battery, good fuses, etc.  You say it did *pop* a bit when trying to start it.  Might be fouled plugs as well.  Honda does not recommend using starting fluid at all, but a SMALL amount shot into the carb box can determine if the issue is fuel flow through the carbs, or something deeper.

You can't get the carbs too clean.  There are some excellent how-tos on this forum and out on the Internets on how to clean the carbs.  Take your time, be thorough, don't force anything, and be meticulous.

Welcome to the forum.  We'll help as much as we can.
Luke M

[LODY]

I have cleaned plenty carbs out and kind of figures that it was something gummed up. The last one i cleaned up only ended up needing gaskets re-seated. Hope it solves the issue. Thanks

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-----Original message-----

From: "LukeM [via Honda CB750'S]" <[hidden email]>
To: LODY <[hidden email]>
Sent: Fri, Jan 11, 2013 13:15:12 GMT+00:00
Subject: Re: Fuel Leakage

Agreed on the need for cleaning the carbs, but make sure you have everything else: good compression, good ignition, clean oil in the case, well-charged battery, good fuses, etc.  You say it did *pop* a bit when trying to start it.  Might be fouled plugs as well.  Honda does not recommend using starting fluid at all, but a SMALL amount shot into the carb box can determine if the issue is fuel flow through the carbs, or something deeper.

You can't get the carbs too clean.  There are some excellent how-tos on this forum and out on the Internets on how to clean the carbs.  Take your time, be thorough, don't force anything, and be meticulous.

Welcome to the forum.  We'll help as much as we can.
Luke M

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NAML

[Hoosier Daddy]

The others are spot on but I am going to try and answer your question more direct.
 The carbs are vented (to the atmosphere). When the float bowls were empty the float dropped and the needle was raised off it's seat. Then it sat... assume that it stuck there. When you finally got fuel to flow, with the needles stuck open that allowed fuel to overflow the bowls and pour out the vents. That was you leak(s).
 Now you mentioned another symptom but didn't ask about it. What you called bleed screws are drains to empty the floatbowls. I think it started on '81's so I doubt if your bike has it, but see if your 1980 has an AFV. A vacuum operated fuel shut off.




It's a valve that if there is no vacuum from the engine running it closes to stop fuel flow. It has been the cause of so much grief it is nicknamed the "Spawn Of Satan" or S.O.S.