float height...

5 replies to this topic
  • sabin

Posted August 23, 2002 - 09:40 PM


Today I decided to play with my flow height as I noticed that my carb is loosing a lot of fuel out of the vent lines. Initially it was about 8-9mm. I made it about 10mm and the bike went lean especially from mid to high. In the Service Manual they say that it has to be 8mm, but on the keihin web site (http://www.keihin-us.com/tune1.htm) they say 9mm??? Does anyone know if there will be any difference and witch one to use?


  • sabin

Posted August 23, 2002 - 10:07 AM


I forgot to mension that I prefer 9mm as it will lose less fuel out of the vent lines...

  • Mark_Cantrell

Posted August 23, 2002 - 04:05 PM


As long as the bowl fuel level is high enough to cover the floats and low enough not to dribble, it's probably OK. I think the lean condition is more from the fuel sloshing below the jets than the difference in sucking fuel up the extra 1mm.

Good luck,

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  • tbronc

Posted August 23, 2002 - 04:30 PM


Check the Patrick Burns Article, near the end he describes what range that it changes the fuel mixture.

Lower measurement (higher level) is richer because it takes less vacuum to draw the fuel up the shorter distance. I believe that they warn not to adjust it more than 2 mm .

.........Just checked the Burns article, it's changed and only says not to adjust it.

Found the old article ver 3.2,...

Float level: Higher float levels richen mixture at full throttle low rpm, and part throttle high rpm, lower leans it, but do not change it more than two millimeters in either direction of 9mm. I have caused myself more headaches playing with float level on FCRs than any other adjustment of the carburetor. If you can possibly run the floats at 9mm, do so. To set float level, with the carbs off the bike and the float bowls removed, hold the carbs in such a manner that the float pivots are above the floats. Tilt the carbs until the float you are adjusting just kisses its float valve needle, but doesn't compress the float needle's internal spring. Measure from the float bowl sealing surface to the highest (lowest with the carbs mounted to the bike) point of the float at a 90 degree angle to the sealing surface. Bend the float tab that touches the little nub on the needle to change the float height.

[ August 23, 2002, 08:05 PM: Message edited by: tbronc ]

  • sabin

Posted August 23, 2002 - 07:15 PM


I opened the carb again and this time I made a tool to measure it, so that I'm sure it is exactly what I think it is. It appeared that it is more than 10mm. I made it 8.5mm and bike now puls as it has to. Thanks for the help guys!


  • Taffy

Posted August 24, 2002 - 03:03 AM


another one of my battles!

i didn't believe in adjusting the carb float and peoples improvements were down to the bike being wrongly carburated and the changes helping and NOT the float height per se.

mr burns has just about got it spot on now and at least he's prepared to change his position on things. good on him-takes a big man to say that.



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