[h60mech]

This new motor I've got has 39mm FCRs (not separates). Today I was riding and stopped on the side of the road to talk. I heard a gurgling sound and saw fuel dripping pretty fast onto the ground. It was coming out of what I'm assuming is a float bowl vent - a black nipple that looks like it should have a fuel line on it, just above where the actual fuel supply hose attaches. Also, with the engine running it would continue to pour out unless I kept the revs up around 3-4000.

My guess is I have a stuck float valve, but I am by no means experienced with carburetors so I'm asking you guys for some advice. I think the hot engine was making the fuel expand in the tank and pushing it to the carbs, which weren't stopping the fuel once it got there.

I've got the carbs off and on the bench and am about to start investigating but I thought I'd start this thread and maybe get some great advice before I get too far into it.

I've looked at Chris Kelley's "Inside the FCRs" page and it looks like I need to take the top panels off (opposite the float bowls) and remove a screw to get to the needles?

Thanks for any help offered!

 

[Muschi]

you are referring to different needles here,
the ones that control the midrange fuel
supply by blocking the squirt from the main
jet are the ones that are accessable if you
take the carburator top off.

the fuel shut off needles are to be find inside
the float bowl connected to the float of course.

i have never opened FCRs yet, sold my 39mm's
without getting to use them, but this should be
the same with any carb i can think of.


for your problem: maybe the return line got
kinked with your last lift of the tank ?
bike is not running okay at iddle because it is
running way too rich as the fuel will be pushed
trough the main jet at all times.
if the fuel return line is okay, i'd check the free
play of the floats and have the shut off needles
replaced probably.

cheers.

 

[h60mech]

Yes! Thanks for the suggestions and information! That's exactly why I started the thread and why I love this forum.

I think the return line was fine but I'll check it out for any signs of me kinking it. Since I got the carbs off I guess I'll go ahead and investigate some and see if I can find anything dirty, etc.

 

[Muschi]

sometimes a single grain of dirt prevents
the fuel shut-off needle to fully close the
fuel entrance.
with a system in use it is more likely that
the viton tip of the needle valve has simply
worn off and got to be replaced though.
you will notice a small ring around the needle's
tip, a sign that it is calling for replacement
probably, at least when the system is leaking
already.

 

[h60mech]

Well, I took off the top plates of the carbs and looked around (partly just to see it). Everything was clean. I then took off the float bowls and floats and inspected the needles and seats and everything - even the drain sumps - was spotless. No sign of wear or rings on the rubber needle tips either.

The fuel lines looked fine and I don't think they were kinked. I took off the check valve attached to the top of the fuel tank and tried to blow through it and it wouldn't let any air pass out of the tank. Completely sealed. I don't know which way it's supposed to go but it seems like pressure building up inside the tank could be causing my problem so I swapped it out with another one that I had that actually lets a little air go both ways. I know that makes it an ineffective check valve but it's just for troubleshooting . . . I guess I could've turned the other one around.

Everything's back together but we'll have to wait and see when I can start it up and get it warmed up tomorrow morning. Kids are asleep now.

 

[desmodue]

As Muschi said, a very tiny speck of dirt, grit, or some crud dislodged from the fuel filter is all it takes for the float needle to get stuck. As you rode the bike home, whatever it was could have easily passed through. I'd pull the guts out of the fuel tank clean it, and install a new fuel filter.

My Keihin's stuck once, but it was very odd, it was during winter storage. The bike hadn't been ridden for a month or longer, but yet one morning I opened the garage to get the truck out to go to work...and the smell of gasoline was very strong. I saw a huge puddle of gas under the SP. After the clean up, I pulled the carbs apart. Nothing, spotless. I mean they were as clean as the day I installed them. No visible wear on the float needle or seat. hmmm. I then opened the tank, there was some bits of gunk, not huge amounts of crud floating about, but still some particulate matter. Cleaned out the tank, swapped the filter for one from NAPA that looked similar, inspected the hoses, buttoned it up. I was going to say something like, never had a problem since...but I know if I did, tomorrow the floor would be flooded with gasoline.

 

[Joe-B]

The fuel tank vent should not let air out of the tank; it's for letting air into the tank as you use up the fuel. You should only be able to blow into the tank through the valve. Those bikes can sit in the sun and get the tank hot and that shouldn't force gas out the carbs. Remember they have a fuel pump in the tank, and a fuel return line. You probably had a tiny piece of dirt in the float bowl valve.
Joe

 

[h60mech]

Well, everything runs great now and not dumping fuel overboard.

Thanks everyone for the info and suggestions!

 

[st2lemans]

I've had that happen with the FCRs on my LeMans, it was a speck of something that wasn't allowing the needle to seat properly.

Another time, I lost about 3 gallons of fuel overnight due to a bad hose (and I hadn't closed the petcocks), nice lake in my garage!

Lastly, the vents on all my bikes vent both ways, and if I fill to the brim and let them sit in the sun, they WILL spew gas out the vent!

Tom

 

[Stopwatch]

I rebuilt my FCR's a few months ago; the o-rings had aged and it was time for a freshening-up ( I had endured the dreaded gas in the crankcase and had no desire to repeat the experience).

Upon first initial start-up after the rebuild everything was fine for a moment, then gas started pouring out somewhere near the tube with the vent you mention that runs between the two carbs. I removed the carbs and replaced the o-rings thinking maybe I had put the wrong size in or maybe it wasn't seated properly. I reinstalled the carbs, turned the key to turn on the fuel pump and gas started pouring out in exactly the same place. At this point I decided I would be buying a lottery ticket that day.

It turns out the plastic 'T' fitting was microscopically cracked and the pressure from the fuel pump was enough to make the plastic expand to let the gas flow through.

Another call to Sudco and another two week wait and I was back on the road.

Over time the seats will wear and as the needle spins with road vibration, etcetera, sometimes the needle makes full contact and sometimes it doesn't, leading to a slow leak.

I'm glad your problem was a little easier to troubleshoot.