1969 - 1976 Sohc Honda CB750 - Kei Hin Float Height Adjustment.

You can get a small (6 inch) T-square at your local auto parts store.  Make sure it has millimeter measurements.

Set the "T" at 26mm.

Now see proof the 26mm measurement for the float height is from the lip around the bottom of the carb body on the '69 thru '76 carbs, not from the gasket surface.

On the left, noticing the angle of the carb, the valve pin tip is not touching the float tang.

At right, the carburetor has been turned counter clockwise (as viewed from the side), so the valve pin tip is just barely touching the float tang, but not compressing the pin.  The pin is spring loaded and will compress if the carb is turned further counter clockwise (too far).  The photo (right) shows the correct angle for checking the correct float height.

(Below)  The measurement is on the CB750 is 26mm, however there is issue as to where the measurement is taken from.  Most believe it is measured from the gasket surface.  I'm not convinced of this information.  Mine is measured from the lip at the bottom of the carburetor where the float bowl is attached.  I did it this way before knowing any of this info.  (using the "T" slider below)

Note:  See float tools below.


I had to photograph this one handed (broke my tripod) so the carb isn't at the proper angle as in the photo above right, but shown is where to place the "T" square in order to get the correct 26mm measurement.  The "T" should just touch the float without compressing the tip of the float pin (as above right).

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This is the only early type float tool I can find.  It is still available from Honda for under $30.  It is also commonly used today by many individuals and professional mechanics for '70s era Kei Hin carburetors.  

You can see below that this tool is not designed to measure from the gasket surface.  You would have to cut slots in each leg in order to do so.

Thanks to "Octane" for the use of this photo!

The carburetor shown is from a mid '70s GL1000 Goldwing, but has the same lip around the carburetor body where the float "bowl" attaches to the bottom, as the '69 thru '76 Kei Hin carbs that came on the Sohc CB750 Honda motorcycles.  The '77 and '78 CV type carbs for the CB750 did not have this lip.

When I purchased and started rebuilding my '76 CB750F Super Sport in early 2000, I went to the local Honda dealer and bought an official Honda Service Manual that was available.  It is indeed a reprint from the original that came out when the motorcycle was manufactured.  In the front of the manual, in the "tools needed" section, it showed the float height tool above, as a required tool, but in the carburetor section of the book it showed the photo to the left.  A completely different tool.

As you can see from this photograph, you can't tell where the float height measurement is being measured from and of course, the manual made no mention of this detail.  I have not as yet found anyone that has actually used this tool, that can verify that the tool begins its measurement at the gasket surface.  I have not seen the original manual, but I doubt that Honda would ever mention such a detail, they just say to use this tool.  I have talked to some Honda dealer mechanics that have at least 20 years of Honda service who state, they measure all the early Kei Hin carburetors from the lip.  I've also talked to a number of well experience Sohc CB owners that state the measurement is from the gasket surface, but none of them actually owned or ever used this tool.  Personally, when I got my '76 CB750F and rebuilt the carburetors, I measured the float height at 26mm from the lip at the bottom of the carb body.  I've continued with this practice, running my CB750F for 6 years and have never had any problem with the float height set from the lip.

I will continue to look for someone that actually owns the early float height tool made for the '69 thru '76 Kei Hin carburetors, in order to verify the setting.  Until then, I can't tell anyone where the measurement is actually taken from.  I know what worked on my bike, but the tolerances and condition varies widely on individual motorcycles that are 30 years old.