Mikuni BST 40 fuel level

[Diego_1100R]

Hi guys,
 somebody who knows the correct height range for these carbs to set fuel level via clear tube gauge?
Setting float height to 14.7 (or 15 mmm) give approximately 5-6mm in fuel height.
Tested on a custom carbs stand, putting the bowls closing surface horizontaly.
My dubt is that with 30+ y.o. plastic floats, could have right away a micro reduicing to their volume. So the mechanical setting can give an incorrect result.

[Jaydee]

1 hour ago, Diego_1100R said:

My dubt is that with 30+ y.o. plastic floats, could have right away a micro reduicing to their volume. So the mechanical setting can give an incorrect result.

Never saw shrinkage on floats on any on the BST Mikuni range. I've worked on many, many sets. The float heights are 14.6mm. But there's a give or take 1mm is this measurement which would phase out influence of a slightly smaller (on a micro scale) float volume. 

With the floats being 30+ years old, the more common problem I see with the BST floats is warping. Where one side of the float is far higher than the other. This is more likely to cause inaccuracies in getting the right fuel level. Sometimes you can gently twist them back level. But some floats return back warped at rest which need replacing. 

I'm guessing your bike is an 11 M or N going by the 40's. I have ever only set up slingshot carbs by float height measurement. 

I find the method you are using is more for down draft carbs that actually have lines cast in to their bodies for a fuel level reference.  No cast lines on BST's to go by so don't see the point.

[Diego_1100R]

Thank you so much for your answer.
I'm happy to hear this from you, because then I can rest assured that I'm on the right path.
Yes, mine is a '91 M, GSX-R 11.

Upon careful observation they do not appear to be deformed as to have one side higher than the other; maybe in a little amount.
To replace them could did cost more than $200; and I replaced already many OEM  components, like pilot jets, main jets, emulsionators, seat valve and needle, rubber diaphragms.
I'll try to stick the floats to the standard value, maybe a little over, 15mm (14,7 + - 1)

Sorry for my bad English, but I'm Italian and as you know we are better with gestures than words!

[Panos]

When i did mine i wanted to use the tube method too but the float covers can't be connected with a tube as they are , so i didn't bother and just measured the floats.

One modification i want to do now is fit a brass tube on float covers so i can use the clear tube method , has anybody done this ?

I found a video of a guy doing this on bandit carbs but he uses one dedicated float cover for this and blocks the next carb needle which is sharing the same fuel line .

I want to have all float covers connected  with clear tube so i can set them all equal , in my head this is the best method am i wrong?

Tube method at 11:40 in video.

 

[Diego_1100R]

Thanks for your contribution. The video is very interesting.
 What I did is approximately the same thing: I made a hollow brass screw M6x0.75 with a connection for the transparent tube. Simply replace the drain screw.
But I made one piece, so I have to measure one at a time.
In the video you can see a level of just 1-2 mm above the bowl closing  surface.
With the correct float setting, I get about 5 mm above that line.
This led to my initial question: how much should it be above this level?
However, after Jaydee's reply I have put my soul at peace, and I will carefully adjust only the height of the float and what happens to the fuel level does not matter.

[Diego_1100R]

This is the piece as I made it:

and this is another interesting video:

https://youtu.be/kcNjF7EdcAs?si=vBWavmQ_xgiuiY3n

 

[Diego_1100R]

Hello folks,
for all those who need to know the final outcome: the engine runs very pleasantly, picking up from 1500rpm in any gear very smoothly. Consumption dropped from an average of 13.5 Km/L to 16.5-17 Km/L. Now I am finally very satisfied