Setting H Float Heights

[Syd]

Just want to clarify what is the correct procedure when setting float heights with the gasket removed as there seems to be a number of statements and instructions about the position the carbs should be in when you set the float heights i.e.; inverted 180 degrees and/or 90 degrees to set the measurement compared to say a 25 degree position or less so not to compress the spring in the valve when you set the measurement? So far, I have found info in old manuals, reprinted manuals and forum information suggesting that any of these methods should be used. I have not been able to find a written procedure from Mikuni around the late 60-70's to confirm the correct method. Should the carbs be positioned at 90 degrees, 180 degrees or say a 25 degrees with no pressure on the valve?

[lc]

Completely inverted (180) works best with these old mikunis,especially when there is wear on the float associated parts..

Other methods often result in an overly rich,dribbling or overflowing resulting from high fuel level in the bowls.

J

[JA-Moo]

The spring is compressed when in use, go 180 for the correct measurement.

[Syd]

Thanks guys, I also agree going for 180 degrees. When you check the old Mikuni VM tuning manual www.mikuni.com/pdf/vmmanual.pdf they show the float height measurement with the carbs at 180 degree as well

[Syd]

One interesting take on this was given to me by a contact in the USA who I have also been talking to who restores classic bikes and is a service manager for a motorcycle shop - see below.

"If the carbs are 180 degrees (upside down) when you set the level, the weight of the float will be compressing the needle spring. And because the strength of the springs can vary (especially with aftermarket needles) the float levels from one carb to the next could be slightly different even though all were set the same. If you set them with no weight on the springs, they will more likely be set correctly. Even if you have a sticking spring in one of the needles."

[tankie]

Set the float height with the cab on it's side, 100 deg from vertical , so the weight the float just closes off the needle valve

[Walms]

I'll play devils advocate on this one...
Upside down or sideways, both are an indirect method IMO. If you want to set the float level accurately, set it at the point it seals... Plain and simple,
As an added bonus, you will be confirming the needle and seat actually function properly.
To do it, you can either blow into the carb inlet or even setup a fixture and use liquid.

[JA-Moo]

how much of a pressure difference can you get from a small spring like that? Nill. Plus the difference would be nowhere near the adjustment range, then take into fact, stuff is going crazy when the motor is running. No need to be ridiculous with this.

[Walms]

The only reason I do it this way is because Keihin carbs have a 2 stage plunger on the seat and it's almost impossible to only make contact without depressing the plunger. For me, this is the easiest way. It also seems everyone who uses them found the same thing.

[Walms]

As far as feeling the pressure difference, there is a mechanical advantage. Don't knock it until you try it!

[Deleted]

What about the float buoyancy? It also takes a certain needle spring tension to overcome the head pressure from the tank for sealing.
Maybe those 2 factors will cancel some of the 180 degree weight on the needle. LOL

The best way should you want to be anal (did not Anal make carbs for Brit stuff? M )is using a tube from the float bowl bottom drain to check the level provided it has a drain nipple (or you make one); which lots of old shit does not employ. So long as you are close and consistent between the three units you're good to go as there is as with everything a CDF technical tolerance.

rt

[Walms]

Still, you find out you have a leaking seat when you hydro lock your motor...

[Ned]

Buy a set of transparent bowls.

I have always used the 180 method.

[Syd]

Thanks for the interesting feedback - sounds like 180 degrees is the way to go..

[Walms]

I get the transparent bowl thing for the visual but how do you know what level is correct, when looking???
It's not like that can be looked up in a manual, or at least I haven't seen it if it does?
You can also use this method... If your carbs piss gas, float too high... If your motor falls flat on its face after distanced wfo, float too low.