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Old 07-22-2005, 03:24 PM   #1
gaspipe OP
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Setting Float Height on Mikuni BST?

After much searching, this is all I could find. It's somewhat cryptic. Would someone please tell me a bit more? Creeper, Loaded, anyone?

Am I to assume the upper edge of the float it to be parallel to the gasket surface when inverted?

Quote:
There is an example of setting the float level on the "service CD". It's under Fuel>Mukini BST40>Setting Float level.

Here is a quote from the service manual. Try and understand this translation.


"Check float level
Take off the float chamber, press down the float frame and hold
carburator as shown in the picture. The float 5 mooves downwards.
Turn carburator slowly until the float moves towards the carburator. In
this position the edge of the float 6 must be parallel to the sealing
surface of the carburator 7.
! CAUTION !
IF YOU HOLD ON TURNING THE CARBURATOR, THE FLOAT WILL PRESS AGAINST THE
SPRING OF THE NEEDLE VALVE AND A CORRECT CHECK IS NOT POSSIBLE. IN THAT
CASE THE CARBURATOR IS TO BE TURNED BACK AND THE CHECK MUST BE DONE
TWICE.
If the two edges are not parallel, correction can be done by bending the
lever of the needle valve. At the end a check is necessary again."

Blame fish [img]images/buttonsCrash/quote.gif[/img]
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Old 07-22-2005, 03:43 PM   #2
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GP... They are refering to the seam on the float where the two halves are joined. That should be parallel to the carb body/bowl gasket surface.
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Old 07-22-2005, 03:48 PM   #3
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Quote:
Originally Posted by creeper
GP... They are refering to the seam on the float where the two halves are joined. That should be parallel to the carb body/bowl gasket surface.
Gotcha. Thanks Creeper.

Now, I'm assuming that this done with the float NOT compressing the spring in the needle......based on the cryptic method in which they hold the carb...?

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Old 07-22-2005, 03:56 PM   #4
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Quote:
Originally Posted by gaspipe
Gotcha. Thanks Creeper.

Now, I'm assuming that this done with the float NOT compressing the spring in the needle......based on the cryptic method in which they hold the carb...?

Yep... tab just resting on the plunger, without any compression.

As I recall ... if you do a "wet test" the fuel level should be 2-3mm below the gasket surface when the hose is held beside the center of the bowl.
Don't hold me to that though.
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Old 07-22-2005, 03:59 PM   #5
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Oooops... ment to say "wet running test" not static.
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Old 07-22-2005, 04:14 PM   #6
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Gotcha. Thanks again. I took a pic so other dumbasses like me would know what they are talking about by lookin' at a pic.



I'll do the wet test as soon as the bike is running. And it's close
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Old 07-22-2005, 04:24 PM   #7
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Nice job on the graphics! ... maybe MeatPop can put in the LC4 List-O-stuff.
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Old 07-22-2005, 04:29 PM   #8
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Nice photo. The first time I did mine the float was quite a bit more than "just touching" the plunger. Bike didn't run. Had to pull the carb back out (which I still haven't figured out how to do in a timely or easy fashion) and start all over. Made damn sure I had it right that second time. Been running great ever since.
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Old 07-22-2005, 04:41 PM   #9
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Quote:
Originally Posted by RedWarrior
Nice photo. The first time I did mine the float was quite a bit more than "just touching" the plunger. Bike didn't run. Had to pull the carb back out (which I still haven't figured out how to do in a timely or easy fashion) and start all over. Made damn sure I had it right that second time. Been running great ever since.
It's a PITA getting the bugger out. I remove the tank, silencer, disconnect the backbone breather, two molex connectors, loosen the airboot clamps, take out the two top subframe bolts to rock it back a couple inches, disconnect the two throttle cables, the choke, and there she blows. Ain't an easy thing to do.

She was right on, but I have the whole bike apart now anyway and figured I'd check it out and make sure the bowl was clean and stuff. I put a new carb slide 'n guide in, the old one was quite worn.

The bike will run like crap if the float isn't very darned close. I'm not in love with the 'precision' of this float arrangement, but it works.
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Old 07-22-2005, 04:59 PM   #10
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Quote:
Originally Posted by gaspipe
I took a pic so other dumbasses like me would know what they are talking about by lookin' at a pic.
Huh? what was that part in the middle?

bookmarked for da index - thanks GP
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Old 07-22-2005, 05:01 PM   #11
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Quote:
Originally Posted by meat popsicle
thanks GP
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Old 07-22-2005, 05:05 PM   #12
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Quote:
Originally Posted by gaspipe
The bike will run like crap if the float isn't very darned close. I'm not in love with the 'precision' of this float arrangement, but it works.
With practice you can check and set the float level with the carb mounted. There's room from the right side. Probably a bit of a pain with the BST because that frame needs to be held.

I take a zip tie and put some .5mm marks on it and then I temporarily tack it onto the side of the carb, such that I can eyeball the bottom of the zip tie against the float reference point. Then I gently hold up the float until the play is gone and make the changes I want.

There is usually a recommended range, and in my case there's 4mm to play around with. So far I've been sticking near the lowest fuel level. Just my preference.
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Old 01-28-2007, 01:59 PM   #13
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I'm feeling like a retard.

This procedure does not make sense to me. I'm all apart and ready to rock, only I'm completely confused by this procedure.

This really doesn't help things.

Take off the float chamber, press down the float frame and hold

carburator as shown in the picture. The float 5 mooves downwards.

Turn carburator slowly until the float moves towards the carburator. In

this position the edge of the float 6 must be parallel to the sealing

surface of the carburator 7.

I can't get an image of this in my head.

S.C.
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Old 01-28-2007, 02:12 PM   #14
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Quote:
Originally Posted by scottcolbath
I'm feeling like a retard.

This procedure does not make sense to me. I'm all apart and ready to rock, only I'm completely confused by this procedure.

This really doesn't help things.

Take off the float chamber, press down the float frame and hold

carburator as shown in the picture. The float 5 mooves downwards.

Turn carburator slowly until the float moves towards the carburator. In

this position the edge of the float 6 must be parallel to the sealing

surface of the carburator 7.

I can't get an image of this in my head.

S.C.
The idea is that you start out with the float pivoted away from the carb body, then you rotate the carb until the float needle just touches the seat. That's the point from where you measure the float height.

The needle has a spring loaded plunger... and if you just turn the carb over, the weight of the float can over-power it and give you the impression that the float is sitting deeper into the carb body than it really is.

Gaspipe's photo gives the impression that the carb is just upside-down... but the carb should actually at about a 35-45 degree angle to measure the float correctly. The "just touching" part is the tip-off.

C
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Old 01-28-2007, 03:26 PM   #15
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Quote:
Originally Posted by creeper
The idea is that you start out with the float pivoted away from the carb body, then you rotate the carb until the float needle just touches the seat. That's the point from where you measure the float height.

The needle has a spring loaded plunger... and if you just turn the carb over, the weight of the float can over-power it and give you the impression that the float is sitting deeper into the carb body than it really is.

Gaspipe's photo gives the impression that the carb is just upside-down... but the carb should actually at about a 35-45 degree angle to measure the float correctly. The "just touching" part is the tip-off.

C
That makes sense now. I took a pic of my carb in what I thought was the same position (Carb upside down) and here's what I got.


Thanks Creep.

S.C.
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