Keihin carb dumps fuel...any ideas?

New Bikes, Old Bikes, Bike Setup, Bike Mods, Questions, Riding Technique, Advice.
Post Reply
User avatar
Brent
Columnist
Columnist
Posts: 632
Joined: Tue Jan 11, 2005 8:39 am
Location: South Bragg
Contact:

Keihin carb dumps fuel...any ideas?

Post by Brent »

I have a 38mm two stroke style keihin carb that wants to dump fuel when it is only half way leaned over on its left side. If I lay the bike over on it's right side, everything is normal...it dumps fuel when the bike is pretty much on the ground. So i took the carb apart, sprayed it out with brake clean and inspected to make sure she was totally clean and that the bladders were operating properly. My first guess was that the fuel had gummed everything up as the bike sat untouched for 5 months. But the carb was very clean, no fuel gel residue and everything was working as per normal. Any ideas out there? I have done nothing to the carb other then what's stated above. I had the bike jetted near perfect and have not touched it in quite a while, so why would the floats start sticking now?
2013 450 XC
2011 YZ 450, 2008 380 XC

User avatar
steve-o
Novelist
Novelist
Posts: 1916
Joined: Sun Jan 06, 2008 7:33 pm

Re: Keihin carb dumps fuel...any ideas?

Post by steve-o »

maybe they aren't sticking but just too high?

User avatar
axel99
2024 RMDRA Member
2024 RMDRA Member
Posts: 1277
Joined: Fri May 26, 2006 9:06 am
Location: Scouting 2017 Dirtier Moose

Re: Keihin carb dumps fuel...any ideas?

Post by axel99 »

Had similar problems with the overflow on my keihin 37mm. Check and set the float level precisely to the recommended specs. If still dumping fuel then increase the float height by 1mm and try again. I made a float gauge out of cardboard, would be better to use some thin aluminum sheet. I find floats can be really sensitive. I ended up setting my floats 1mm out of spec, now it only leaks fuel when I am lying on the ground with the bike beside me in a horizontal position :lol:. I seem to get better mileage also, duhhhh!

Is it possible your floats have a hairline crack and they have absorbed some fuel? Maybe let them dry out for a couple days as a last resort to trouble shoot.
#Z3B

rock93
Writer
Writer
Posts: 149
Joined: Tue Sep 23, 2008 10:00 am

Re: Keihin carb dumps fuel...any ideas?

Post by rock93 »

Another thing to check is the little spring loaded pin that is inside the float needle if it is binding and not coming back out smoothly after you push it into the needle that will cause you problems.

trailguy
2024 RMDRA Member
2024 RMDRA Member
Posts: 1190
Joined: Fri May 23, 2008 6:18 pm

Re: Keihin carb dumps fuel...any ideas?

Post by trailguy »

Brent pull the float needle out a inspect the rubber end. Sometimes after the bike has sat for a long period of time the rubber will develop a slight groove or indent & this will cause your problem.If the rubber end is perfect I would adjust the float level slightly to lower the fuel level in the bowl. :cheers:

Zeal
Journalist
Journalist
Posts: 488
Joined: Fri Sep 08, 2006 3:46 pm
Location: Calgary

Re: Keihin carb dumps fuel...any ideas?

Post by Zeal »

I think it may be the float level, although it is strange that it only happens on one side. I had to adjust the float level on both of my Gassers (08 and 10), and know that Shannon and Wes did the same.
08 GasGas (That's the Brand fool!)
250 EC

#999 Int.

User avatar
Brent
Columnist
Columnist
Posts: 632
Joined: Tue Jan 11, 2005 8:39 am
Location: South Bragg
Contact:

Re: Keihin carb dumps fuel...any ideas?

Post by Brent »

ya it is a little strange that it only dumps out of one side...plus the fact that it has always been perfect and i haven't touched a thing makes me think that adjusting the float height isn't necessary, but i will inspect that to make sure. I think i will have a look at the O ring and spring combo and see if Trailguy might be right. Thanks for the ideas though.

Maybe it will get better if i go for a good 4 hour ride over really harsh terrain?? kinda just slam it back into place. LOL
2013 450 XC
2011 YZ 450, 2008 380 XC

Ynot303
2024 RMDRA Member
2024 RMDRA Member
Posts: 1313
Joined: Thu Mar 15, 2007 7:46 pm
Location: Calgary

Re: Keihin carb dumps fuel...any ideas?

Post by Ynot303 »

Brent wrote: Maybe it will get better if i go for a good 4 hour ride over really harsh terrain?? kinda just slam it back into place. LOL
Sounds more fun than huffing gas in the garage. :thumbsup:
2024 RMDRA Treasurer - #303

User avatar
axel99
2024 RMDRA Member
2024 RMDRA Member
Posts: 1277
Joined: Fri May 26, 2006 9:06 am
Location: Scouting 2017 Dirtier Moose

Re: Keihin carb dumps fuel...any ideas?

Post by axel99 »

I stumbled across this how-to article while looking for something else. I don't want to start a jetting discussion but the how-to on setting float levels has some good info.

http://ktmtalk.com/index.php?showtopic=419620
http://www.thumpertalk.com/forum/showpo ... ostcount=1
#Z3B

User avatar
cladoo
2024 RMDRA Member
2024 RMDRA Member
Posts: 1080
Joined: Sun Dec 12, 2004 9:51 pm
Location: Okotoks, AB

Re: Keihin carb dumps fuel...any ideas?

Post by cladoo »

Go to gasgasrider.org and look up how to set your float height. That would be your problem. I had the same trouble on mine until I set the float level.
Claude

User avatar
Brent
Columnist
Columnist
Posts: 632
Joined: Tue Jan 11, 2005 8:39 am
Location: South Bragg
Contact:

Re: Keihin carb dumps fuel...any ideas?

Post by Brent »

ended up being just a blocked vent line, that's what caused the one side dump problem. It's great when it ends up being something simple. The floats on my bike have been perfect since day 1.
2013 450 XC
2011 YZ 450, 2008 380 XC

Post Reply