Mikuni Float Height

freedomgli

freedomgli

Been Around the Block
So I'm double checking everything on my new THR tuned Mikuni VM30 carbs before I put gas through them for the first time and I notice the floats are not set to the right measurement. My Mikuni Tuning Manual says 22-24mm (as measured from the gasket surface to the bottom of the float) but these were like 30mm+ and look as though they haven't been touched as the tang on the float arm that presses against the needle valve is flat and even with the rest of the float arm.

Getting the right measurement is a challenge as my carbs have twin independent floats that ride on brass slides pressed into the float bowl so when I invert the carb and pull the float bowl off the floats have no support as they're not actually attached to the float arm. I fiddled around with some wire in an attempt to hold the floats in place sans float bowl but it was no use so I decided to take my measurement directly from the float arm and add 9mm to it. I measured the floats and they're 37mm tall and the pin that acts on the float arm is 9mm from the bottom of the float. I figure I'll attach a hose to the fuel inlet and blow through it so I know exactly when the needle valve is open or closed. Is this sound reasoning?

But others have said that adjusting the float level is a poor method for setting up carbs and that I should use a liquid column manometer to measure the actual fuel level in the float bowl. I've read some very generic advice that the fuel level should be 3mm below the gasket surface but I can't actually find an official spec for my carbs.
img-1084607422.jpg


Others still have said that the float arm should be parallel with the gasket surface when the needle valve is closed.

Which method is best? Any tips on adjusting the float height with the twin independent floats? I found this float gauge on a Kawasaki Triple website but it doesn't have provisions for twin independent floats. Thanks for your help! I'm new to carbs.
 
Do you have this tuning manual? It helps a lot.

http://www.mikuni.com/pdf/vmmanual.pdf
 
freedomgli said:
Others still have said that the float arm should be parallel with the gasket surface when the needle valve is closed.
Click to expand...


I posted reply at Caferacer.net.
manometer?
its just a tube with markings every millimeter connected to float bowl drain spigot
 
djelliott said:
Do you have this tuning manual? It helps a lot.

http://www.mikuni.com/pdf/vmmanual.pdf
Click to expand...
Yes I have it. No it does not help answer my question. I'm seeking clarification on how to best deal with twin independent floats which did not exist when that simple tuning manual was published ~30 years ago. Thanks anyways.
 
Page 16 of that manual: http://www.mikuni.com/pdf/vmmanual.pdf talks specifically about setting float height on the independent float style carbs.

That whole manual is for the VM carbs with the two floats. I have the same carbs (VM34's) on my XS650.
 
Tim said:
Page 16 of that manual: http://www.mikuni.com/pdf/vmmanual.pdf talks specifically about setting float height on the independent float style carbs.
Click to expand...
Sorry, you are correct. But the diagram isn't very helpful as I already know what the measurement is supposed to be but I am having trouble actually taking an accurate measurement. When I invert the carbs and pull the float bowl off to inspect the float height the floats are literally floating in free space not attached to anything. They are not attached to the float arm as the floats ride up and down on brass slides which are no longer existent when I pull the float bowl to do the measurement. How do you handle it on your carbs? I tried lifting the float bowl off just enough to clear the bottom of the floats and keep them supported but it is useless. I can't get in there with a gauge with the float bowl partially removed and when I totally remove it the floats have no support and are not attached to anything.

I have Type A independent floats as shown in the Sudco catalog item #24

http://www.sudco.com/CatalogJPG/123.jpg
 
Where are you trying to measure?
the floats are not needed, your only measuring the arm position with carb inverted.
Fuel level is with carbs on bike and a piece of pipe connected to drain spigot, loosen float bowl drain screwand see where fuel level stops
 
crazypj said:
Where are you trying to measure?
Click to expand...
As far as I can tell I'm supposed to invert the carb, remove float bowl, press the float arm down until the needle valve is closed and then measure the distance from the gasket surface to the bottom of the float (now the top since the carb is inverted). The problem with these instructions is that I cannot measure from the gasket surface to the bottom of the float with the float bowl removed since the floats have no support as they're not attached to the float arm. This is why I figured I could instead measure the distance from the gasket surface to the float arm and then add 9mm to achieve the same value as if I had measured from the gasket surface to the bottom of the float (assuming for a moment my carbs were equipped with the traditional twin type floats which more easily allow such a measurement to be taken). The tricky part about measuring the distance from the gasket surface to the float arm and then adding 9mm is that the float arm is not parallel with the gasket surface at the specified 22-24mm distance so it really matters where you place your gauge along the float arm to take the reading. Hence, my question about which is the best method to get the most accurate float height.

Am I missing something? Is the 22-24mm specification from the gasket surface to the float arm? Everything I've read says that spec is from the gasket surface to the bottom of the float.
 
YES,
Your missing something,
The ability to follow very simple instuctions
Floats have nothing to do with anything.
It's a generic picture your trying to work with.
Ignore it
Just set arm level with gasket surface, sitting on it's own weight.
It will come out around 22mm, your overthinking a non-problem which is creating problem
 
And I was going to ask if it was running bad ;D I have 2 stroke carbs supplied from winners circle(vm 30's) float height was not an issue,,,,,,,,jetting was ::)
 
crazypj said:
Just set arm level with gasket surface, sitting on it's own weight.
It will come out around 22mm, your overthinking a non-problem which is creating problem
Click to expand...

Thanks dude! I knew I was over thinking it. I was always looking at a poorly printed copy of the manual you linked to and I didn't realize that for independent floats the specification is the distance measured from the gasket surface to the float arm. The distance from the gasket surface to the bottom of the float is only applicable to twin type floats. Reading your post and looking at the image again blown up on my 23" monitor it finally makes sense to me now. Duh. It took me long enough!
 
Armed with a new found understanding I successfully checked and adjusted the float height on my carbs today. When the float arm is parallel with the gasket surface the distance is ~22-24mm per the spec in the Mikuni Tuning Manual. Both of my carbs needed just a slight adjustment and probably would have run fine as delivered new. To make my life easier I took an old plastic Safeway Club card and cut it up according to this template to make a simple float height gauge. Carbs now installed on the bike. I just need to do the mechanical sync (idle screw then cable adjusters) and then oil my UNI filters.
 
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