Mikuni BS28 Dry Float Height Spec (XJ550 Seca) Carburator

After doing some searching for a float height measurement I see that there are a few differing opinions.

Does anyone know the correct spec for the Mikuni BS28, preferably in mm? Thank you.

 

The documentation I have doesn't list a dry setting, but it's best to set them wet in any event. If you haven't seen this file already, it says 2mm +/- 1mm for the fuel level.

 

There is no "official dry setting" for the Mikunis that I'm aware of.

Gotta wet-set them, +/-1mm is just too small.

 

Re: Mikuni BS28 Dry Float Height Spec (XJ550 Seca) Carburato

Yamaha used to list a dry height for the 81 XJ550 in their parts fiche. They dropped that specifications page several years ago.

According to a post I made back then the height was 21.5mm. I believe the tolerance was +/- 0.5mm.

We've had debates about how good the dry height is. I used to be able to say that I never saw one where the wet was out when I had a dry spec. Just recently though I had an XS1100S where the dry height was set to spec and the fuel levels were up to 7mm low. So I can't say that any more.

Use the dry to get in the ballpark, but use the wet check to verify your result.

 

Thanks everyone. I'll rely on the fuel level in the bowl.

 

So I was reading this today to find out if any dry settings would be a good starting point going to wet setting.

I found online this tutorial about rebuilding similar carbs
http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

They mention 22.4 as the dry set height.

When I was trying to dry set my floats I noticed that one side of the float is higher that the other on all 4 carbs. At first I thought it was me but using the carb rail as reference I took pictures and you can see one side flush and one protudes from the rail.

That being said, I am not trusting this dry setting and really checking the wet set.

 

dry setting your carbs is a waste of time. Take the measurements, do a wet fuel check , if you are lucky enough to get a bowl in spec you can use that height as a base line to set your other bowls to if they are out of spec.
it could be the setting you have when you took the carbs apart was dead on for fuel height, why mess with it???
the float height gives you a line to measure against as you adjust your float height to correct the wet test results
also remember that that spec is for oem needle valves because aftermarket can be different lengths.
the floats have been bent and rebent over the years it is a suprise they still float

the only time I would think it may be needed to dry set is if you were putting a new float in the carb

 

I would agree that if you use The same needle, needle valve, and floats… Then you might be able to leave the floats as is.

But, if you change needles and/or float valve You should go back to factory basic settings and then dial-in from there, Simply because everything is based off of a starting position. True, new needles have different Lengths so you must start from a baseline again.

Ecologito, when I set floats I set both sides

 

looking to purchase an entire carb rail for Yamaha 83 Xj550. Mikuni BS28...Anyone have a lead on a shop, site, or individual who talk turkey?

 

face book Yamaha carbs group he has quite a few carbs all rebuilt

https://www.facebook.com/groups/324278634619273

 

I have been dry setting my floats successfully. Once the carbs are assembled I check the wet level and rarely need to adjust.

If you have a good spec for the dry height and are meticulous about the procedure, you should be able to reliably set the floats. That said, I would always verify the wet setting.

 

Jason, I’m near Utica— send me a private message