Float heights

Im setting my float heights using the clear tube method. Took me quite awhile to level them to my liking, but I'm there. I measured carb 4 and the level was right on spec - 2mm for my 550 mikuni's.

According to the fuel levels pdf, you can use a slide measuring device to measure a known good carb, which i've confirmed, and then set the others to match.

My question is: Do I need to have the carbs at the 60-75 degree angle (where the floats just barely touch the valve spring-tips) that the PDF mentions while measuring the floats this way, or do I need them perfectly level?

It seems like a ridiculously difficult thing to hold the carbs at the magic stars-are-aligned angle, while simultaneously measuring the floats with any level of precision.

Would i just be better off using the clear tube on the other 3 carbs? Seems like it would be less complicated, although more time consuming.

 

Just use the clear tube method; unless you did something really radical they'll be close.

That "dry-setting by comparison" method is still only a starting place; you STILL NEED to VERIFY them all, individually, using the clear tube method.

 

You may also want to try this method.....
http://www.xjbikes.com/Forums/viewtopic/t=31559.html

 

Gotcha, then I will just do that.

When it comes to using the clear tube on the middle carbs, 2 and 3, how does one get a good view of the clear tube along side the carb?

Or can i simply rotate floats on the same bowl, adjusting them as i go?

 

Depending on your method of "mounting" the rack to work on it, you should be able to get a good view on 2 and 3; at least decent enough to be able to tell what's happening.

NO, you can't use one carb to adjust all the floats with, that defeats the puurpose of checking each one.

 

You needn't hold the tube alongside the 2 and 3 carbs to read the levels. If the rack is level (and it should be to work accurately anyhow) you can read them against the outside bodies.

 

Oh come on. Read #3 by holding it up against #4?

I dunno. Possible in theory; I concede. But on the bench? Within +/- 1mm? Mikunis, remember? Hmm... I gotta try that, and compare.

The real answer to the question comes from a wizened old instructor I had in adding machine school nearly 40 years ago:

"how th' hell do you---"

"Manual dexterity, son; manual dexterity."

I have a Wilton 4 1/2" bench vise that I pad with cardboard and clamp the rack in. Since my bench is already perfectly level in all directions, getting the rack likewise is easy. Using a pair of hemostats, I've always been able to hold my graduated tube (thanks, Len) up against the side of the carb in question.

It just takes...

manual dexterity.

But try Carl's method. He is after all, a trained professional. Honest, I'm not being a...

 

Yes. The book says as much.

My thing is that when I'm doing it using the graduated tube I got from Len, the hose that came with it is rather long. While I can loop it around to get it where I want it to go (manual dexterity, son) I fear having that much hose hanging below the bowl is throwing off the measurement.

 

MiCarl is right. Fuel height measurement will NOT be thrown off by using extra tubing to measure an inner carb by holding against an outer carb provided the rack is LEVEL, and assembled correctly (carb body/float bowl mounting surfaces are in-plane)! And assuming, of course, that you have enough fuel in your tank for all that extra tubing.

It's the same principle that allows you to switch around float bowls to make measurements when you couldn't get one of the drain screws out. What happens below the float has no effect on the height that the float will shut off the fuel. If you made custom float bowls that were twice as deep, you'd get the same measurement...and performance (hydrostatic pressure is the same, and it's the difference between hydrostatic pressure+atm, and venturi pressure that draws the fuel up). You'd just have a lot more gas sitting in the carbs instead of the tank.

 

If the bike is level, then I got no problem with that.