Topic: 1977 or 1978 CB750A Carb Float Setting

[raymond10078]

I have a 1978 CB750A that I am trying to revive from the dead.

The carbs use "flat bottom" floats.  The factory manual indicates that the float setting should be set at 12.5mm.  The factory manual also shows two pictures, which differ from one another.  One picture directs that the float be set by measuring at the middle of the float (in-line with the main jet).  Another picture shows the level being set at the end of the float (towards the front of the bike).  This second picture also shows the flat portion of the float level with the carb flange.

The reason that I'm asking this very basic question is because when I set the floats to 12.5mm (using either method), the floats don't set level (with the carb bowl flange).  My past experience with floats (that are flat) is that the flat portion generally sets level with the carb bowl flange (which agrees with the second pic in the shop manual).

In this case, I'm guessing/wondering that a past owner has installed a set of floats from a 1976 CB750A (which has a 14.5 mm float setting).  The floats that I have, if set to 14.5mm, are level with the carb flange.

So, after all of these words, for other 1977 or 1978 CB750A owners - when you've set your floats, are they (the flat bottoms) level with the carb flange, or are they sloped?  Did you set the level across the main jet? 

[05c50]

The correct setting is 12.5 and yes my floats were even with the carb flange. A few questions. Are you setting the floats with the carbs on the bike or off with the carbs held upside down? The reason I ask is that either way can lead to inaccurate settings. Are you aware that when setting the floats, the little springs in the needle valve should not be compressed. The picture in the manual shows the float being measured with carb being held with the throttle bore facing up, so as not to put excessive pressure on the needle springs. Maybe you already know this, but I have seen this mistake cause lots of anguish.......been there, done that. 

.........Paul

[raymond10078]

Yes, I am setting the floats with the carbs off of the bike, with the carb throats points pretty much straight down, so that the float valve spring is just barely touched, but not compressed.

The only thing that makes sense is that I've got a set of 1976 floats in my 1978 PD43A carbs.

[05c50]

i can take a picture of a 77 float for comparison if that would help.

...........Paul

[raymond10078]

Yes, a picture might be very helpful.  Especially if a tape measure or something with a common scale is included.  Thank you Paul

[05c50]

Hope this helps



.......Paul