Oh great motorcycle techies.. Help with a 83 CB1000C problem...

[hootmon]

I need some theoretical extrapolation from you great techie heads...
Yes I understand all of your crystal balls are in the shop...

I have a friend who has a 83 Honda CB 1000 Custom...

***Here is where the weird starts... ***
The bike just recently started having a problem...
When he starts the bike, gas pours out and onto the ground.. He thinks from the vent tube, but I haven't looked yet, so it could be from a carb...
Turns off the bike, and the leaking stops..
He has opened the gas cap while it is running, and the gas keep pouring out... , so it is NOT a fuel tank pressure thing.. The tank is no longer full (since it has leaked gas out), so it's not an overflow thing..
***Here is where the weird stops***
I am going over to his house on Monday to look at it, and want to have some suggestions on possibilities... Can any of you think of a situation where gas would be forced out of a carb and onto the ground, only when a engine is running??? or out the vent tube with the cap open???
I'm just looking for some suggestions here...
***Hootmon is bowing to the techie weenies...***

[Chad in Michigan]

does it have a fuel pump? if it does, whatever shuts off the flow may not be turning off.. not familiar with anything other than 3rd gens, but i remember someone saying some of the older ones had fuel pumps. just a shot in the dark, vary dark, lol.

[roboto65]

The floats are sticking in the Carbs well the needles on the floats to be exact when it happens again try tapping the carbs with a screwdriver handle and see if it stops but all in all they need to be rebuilt !!!!

[drkngas]

stuck float.  time to clean or rebuild the carbs

[hootmon]

The Carbs were re-built not to long ago... Maybe 2K or 3 K miles.
I do not believe there is a fuel pump, but gravity fed like most in-line 4 cruisers... I will dig in a little deeper on Monday... In the mean time I'll have my friend check his manual to see if it states whether it has a fuel pump or not...
Thanx for the input !!! We will get to the bottom of it yet, and I will look to see where the fuel is coming from and do the Tap, Tap, Tap thing on the related carb, if that is where the fuel is coming from.

[roboto65]

I will bet on the float or float needle. On the CBs you might be able to get to the float bowl and check it on the bike but I pretty much guarantee it is the float  or needle

[TLRam1]

Depends how much is flowing and where from.

Too bad I deleted all my photos of my episode I had on a Vulcan 800. It gushed, like a waterfall out of the carb. breather area when the bike was running.

What happened was the crankcase vented to the carbs, while sitting the carbs would leak gas down the vent tube into the crankcase (float needle) and fill up the crankcase with gas/oil mixture. When you start the motor the crankcase fluids were pushed back up the vent tube and out through the carbs.

[roboto65]

Also it could have a auto shutoff like we have on our 3rd gens that is vacuum operated and only opens when the engine is running so when he is running the valve is open and out comes the fuel because the float is stuck or sticking open !!!

[Charles S Otwell]

If you have to pull the carb down be sure to check the  floats themselves for small cracks or the plastic floats that have lost there buoyancy

[dgc67]

From my experience I would bet my 110% on a float sticking or some gunk got under the needle and is not allowing it to close.  Happened alot on my 82 Maxim 650.  I would pull the carbs and there would be some whitish, almost like wet toilet paper, gunk in under the needle holding it up.  Fuel filter and thourough flushing of fuel lines.

[MagnaDaddy]

My CB900 is having a similar problem even after I changed out the float valves.  From what the guys on the CB forums say these valves have a bad habit of getting junk stuck in them as the "filtering" on these bikes is pretty lame from the factory.  I'm pulling my carbs back out to double check the float valve seats and check the inline filter to make sure it is working.  BTW: Gas IS gravity feed.

[hootmon]

Thank you all for your wisdom...
I'm hoping it is one of the outside carbs..
if so, is this something that might be able to be corrected without removing all the carbs???

[dgc67]

You should only have to pull the bowl from the offending carb(s).  this can be done if you have a small screw driver.  I have one that bends 45 degrees an inch or so from the tip and gets in tight spots pretty good and have done it before, but stripped the screws a little in the process.

[Greg Cothern]

Fire it up!  Well maybe a bad choice of words    Start it up, take a wooden handled screwdrive and gently but firmly tap the carb bowls where the carb body and bowl meet several times.  Sometimes if its a stuck float this will dislodge it.
If it does run seafoam through it.

[MagnaDaddy]

FYI
Pulling the carbs on a CB750/900/1000 is a piece of cake compared to the Magna!  I'd do it just so you can take a good look into what's going on.