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Joined: Feb 23, 2007 Posts: 1045 Location: Orlando, FL
Posted: Wed Sep 22, 2010 11:36 am Post subject: Setting Float Levels - A Discussion
I'm involved in a float-level discussion on a Yamaha XJ forum I frequent (specific for my Seca 550).
Yamaha, on all the Seca and Maxim motors, does NOT give a float level specification by measuring from a fixed carb body point to a point on the float at the moment the needle valve seats. They only give a specification of actual fuel level relative to an external carb body point measured via a clear external tube. That is, hold the carb level, attach a clear tube to the bowl's drain port and hold open end of tube above the bowl gasket, attach a fuel source to carb, fill carb and open drain screw. Fuel in the external tube will show the actual fuel level in the carb. Measure THIS. Adjust float tang accordingly. The factory manuals and all the aftermarket manuals describe it this way.
My position is that this seems like WAY more effort than ought to be necessary. The 'dry' float level measurement (carbs apart on the bench) is how most of the rest of the industry works. However, many of the more experienced Yamaha dudes maintain that the ONLY way to do this is the 'wet' method. Too inaccurate to do it the other way. Too much variability - that is, set 'dry' as best as can be will STILL lead to unacceptable variation in the 'wet' method.
Further, I'm interested in how tight the tolerances all seem to be. They swear up and down that the resulting dimension has to be right on the gnat's a$$ or the bike won't like it at all. For example, on my Seca 550, the spec is 3mm +/- 1mm fuel level in the external tube below the carb body bowl flange. And they all swear that it REALLY needs to be at 3mm, +/- 0 to be happiest.
I'm kinda of the opinion that when riding, the bike (and carbs), bounces, pitches, rolls, sags, vibrates, and generally moves around so dang much that it's hard to believe the fuel level in the carbs is doing anything OTHER than just sloshing around!! +/- zero millimeters, my a$$... And, the float bowl is ~2" or 50mm deep. Is the level in the bowls THAT critical? I look at a ruler and 1 mm is hardly anything compared to the sloshing that must be going on inside that carb bowl when underway...
And yet... I remember how sensitive my own CB200 was to float level... And Stu has posted in the Suzuki forum about how his own GT500 is much happier by having made a 1.5mm change.
Posted: Wed Sep 22, 2010 12:54 pm Post subject: Re: Setting Float Levels - A Discussion
KirkN wrote:
I'm involved in a float-level discussion on a Yamaha XJ forum I frequent (specific for my Seca 550).
Yamaha, on all the Seca and Maxim motors, does NOT give a float level specification by measuring from a fixed carb body point to a point on the float at the moment the needle valve seats. They only give a specification of actual fuel level relative to an external carb body point measured via a clear external tube. That is, hold the carb level, attach a clear tube to the bowl's drain port and hold open end of tube above the bowl gasket, attach a fuel source to carb, fill carb and open drain screw. Fuel in the external tube will show the actual fuel level in the carb. Measure THIS. Adjust float tang accordingly. The factory manuals and all the aftermarket manuals describe it this way.
My position is that this seems like WAY more effort than ought to be necessary. The 'dry' float level measurement (carbs apart on the bench) is how most of the rest of the industry works. However, many of the more experienced Yamaha dudes maintain that the ONLY way to do this is the 'wet' method. Too inaccurate to do it the other way. Too much variability - that is, set 'dry' as best as can be will STILL lead to unacceptable variation in the 'wet' method.
Further, I'm interested in how tight the tolerances all seem to be. They swear up and down that the resulting dimension has to be right on the gnat's a$$ or the bike won't like it at all. For example, on my Seca 550, the spec is 3mm +/- 1mm fuel level in the external tube below the carb body bowl flange. And they all swear that it REALLY needs to be at 3mm, +/- 0 to be happiest.
I'm kinda of the opinion that when riding, the bike (and carbs), bounces, pitches, rolls, sags, vibrates, and generally moves around so dang much that it's hard to believe the fuel level in the carbs is doing anything OTHER than just sloshing around!! +/- zero millimeters, my a$$... And, the float bowl is ~2" or 50mm deep. Is the level in the bowls THAT critical? I look at a ruler and 1 mm is hardly anything compared to the sloshing that must be going on inside that carb bowl when underway...
And yet... I remember how sensitive my own CB200 was to float level... And Stu has posted in the Suzuki forum about how his own GT500 is much happier by having made a 1.5mm change.
Any thoughts on the subject?
Kirk
I believe Yamaha DOES give an "installed" float level spec. What year is your bike? If it's a 1981, my spec sheet says 30mm. The "installed" spec is what the factory uses and if measured correctly should result in a "wet" measurement that is in spec. I don't have a factory manual but do have the factory spec book I used as a dealership mechanic back in the late 70s and 80s. I've also seen the installed spec on the microfiche card in the specification section.
I agree the "wet" measurement is more accurate but agree with you on the tolerance issue. As long as the level allows for enough fuel to keep the jets submerged without being so high that overflow into the venturi or overflow vent happens, then all should be good.
it's not rocket science. It's a frigging toilet valve.
Any slight changes to float level that results in an overly rich or lean condition just means the float was set too low or high to begin with.
Joined: Dec 26, 2007 Posts: 1283 Location: Scottsdale, Arizona
Posted: Thu Nov 04, 2010 7:44 am Post subject: Re: Setting Float Levels - A Discussion
KirkN wrote:
My position is that this seems like WAY more effort than ought to be necessary. The 'dry' float level measurement (carbs apart on the bench) is how most of the rest of the industry works. However, many of the more experienced Yamaha dudes maintain that the ONLY way to do this is the 'wet' method. Too inaccurate to do it the other way. Too much variability - that is, set 'dry' as best as can be will STILL lead to unacceptable variation in the 'wet' method.
Kirk
Those dudes are correct. Kawasaki discovered this back in the '70s and began issuing wet fuel level specs. The fact that the carbs will be leaning and bouncing makes it all the more important to get as close as possible to that knat's a$$. Dry setting works pretty well, as long as everything in the float bowl is in new condition - floats and float arms haven't been tweaked. After one or two folks have monkeyed around with the floats, all bets are off. But wet setting will overcome those problems. Inability to balance idle mixtures on multi-cylinder engines and slow return to idle rpm are symptoms of uneven fuel levels.
Joined: May 28, 2009 Posts: 423 Location: chicago area
Posted: Thu Nov 04, 2010 1:09 pm Post subject:
hey kirk, which XJ site would that be, im involved with one that doesnt believe in "messing with the magic motor" in the least, to the point of being almost MEAN when you mention rejetting or pod filters.
obviously i need a better site.
ductune and stu thanks for the info, and the backing up of "those dudes" now ill be able to set em right when i get it that far!
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And, the float bowl is ~2" or 50mm deep. Is the level in the bowls THAT critical? I look at a ruler and 1 mm is hardly anything compared to the sloshing that must be going on inside that carb bowl when underway...
