Help with Mikuni BS34 float height

Hi!

Im getting close to firing up my bike for the first time after some restoration work (project thread), and did the clear tube check yesterday on the carb. 2 years ago I cleaned the carb good and put in new keyster kits. I never did the clear tube test though.

Well, the test indicated quite good level in 3 bowls (-1 mm, -2 mm and -3 mm below bowl edge) but one sat at +10 mm! I drained the carb and checked the static height measurement which showed 18,9 mm (18,6 is stated in manual), as I understand, a bigger measurement will give a lower level here so if anything, this bowl would be low?

How do I proceed from here? I guess the float itself can be bad or the float needle is not sealing properly? Also, the carb has been sitting for almost 1 year, could it have getting stuck so maybe I should fill it up again and do another try?

I also read somewhere that the floats can get stuck in fully open because they are allowed to travel to much, so reducing that with the upper tang can also help?

Another question, I will attempt to adjust the carb bowl that was sitting at -1 mm and getting it closer to -3 mm which is the reference, how much would that be on the float heigh? anyone has a feeling of that? divide by 10-15 something?

 

thanks in advance!

Regarding the possibility of float needle not sealing : With carbs on bench and bowl off blow into the fuel line. It takes an awfull lit of puff to lift a float. I cant di it. It the needle valve is not sealing you will hear it. Remove float and valve and clean the seat wit a Q tip and Brasso.

Regarding the float adjustment : If you change the float height by x mm it will change the fuel level by the same x mm. At the end of the day the correct float height is the one that gives you the correct fuel level regardless of what spec is in the manual.

 

One easy mistake is to install the float upside down.

Thanks for the advices, just to clarify: Is it possible to install the float needle upside down?

...and im not sure I understand the air test either. Should I press down the floats and listen if I can hear air escaping while blowing air into the fuel line?

Edit. Update, I tried blowing into the fuel line, not to over think it, but as expected air seems to be escaping most everywhere, probably through the remaining 3 float valves.

Not really possible to get the float needle upside down, but the floats can be installed upside down.

To do the blow test, the carburetors have to be off the bike and upside down.

On the carbs I have been into, there is a small wire hook on each float valve that hooks over the adjunct tab on the float. I do not see it in the picture.

Ok, I have worked with the carb now for a couple of days and there doesnt seem to be a problem with the float height on no 3 that I thought. Either the level was high because it had been sitting for a year, or that I made a mistake by moving the clear tube both up and down. The "blow test" also checks out fine now!

I have made a couple of errors with the clear tube method along the way, both getting air bubbles blocking it and moving it both up and down. Now I fix the tube, then after the bubbles are out, I lower it a couple of times and check that the measurements is the same and that no new bubbles is present.

After 4 attempts all levels sit at -4 to -5 mm. Very balanced, but they should be a tad bit higher according to the manual (3 mm +-1).

What do you think, go another round with it and try to get 2-3 range or leave it at 4-5?

TexasKZ wrote:

On the carbs I have been into, there is a small wire hook on each float valve that hooks over the adjunct tab on the float. I do not see it in the picture.
 

I  checked a couple of pictures online and there is also one in the clymer, and these KZ BS34 seems to look like this, nothing is missing what I can tell. But thanks for the heads up!

I'd leave the levels alone.  1mm low is NO PROBLEM, and much better than a high level, which can cause overflowing.

I'm about ready to button up my BS34's on a 750 so this was a good read. Does tapping the carb bowl and moving the clear tube up and down get the bubbles out? Also is the clear tube method performed with carbs installed on the bike or off? I'd prefer to do it on the bench. Do you just make sure the carbs are level front to back and side to side?

atownbrg wrote:

I'm about ready to button up my BS34's on a 750 so this was a good read. Does tapping the carb bowl and moving the clear tube up and down get the bubbles out? Also is the clear tube method performed with carbs installed on the bike or off? I'd prefer to do it on the bench. Do you just make sure the carbs are level front to back and side to side?
 

I will try to answer with my limited experience of this.

I think you can do it both on bike or off, but much more convienient off bike. Im doing it with the carbs level in both directions on a small mobile carpenter bench, fixing the carb in the middle.

You should avoid moving the clear tube both up and down, only down is ok,  as you will push fuel back up in the bowl if you reduce the volume of the clear tube. I let the air out by squeezing the tube where it connects to the drain on the bowl and moving it side to side carefully, so that the air get out. When it looks good, I start moving the tube down in small steps until I see no bubbles following down from the drain pipe.

Is probably OK to both move the tube up and down as well, as long as you move it down more than up before taking the final measurements, so that the bowl isn't overfilled.

Jonas, thanks for the reply. This last little bit of the carb setup has me a little hesitant so I've been procrastinating a little...