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Old 06-16-2013, 01:50 PM   #11
Brevis illi vita est
Joined: Jun 2010
Oddometer: 4,615
Originally Posted by 190e View Post
This is a really interesting thread - at least when it sticks to talking about carbs.


When you say the carbs are very sensitive to fuel level I always think that the most important thing is that the levels are as equal as possible for both carbs. So from your observations just how close to equal do they need to be. 1mm or less ?

Also from the same observations did you notice that the sensitivity to level varied at different throttle openings ? In other words if you have a level difference between the carbs where does it have the biggest impact.

For what It's worth I think 24mm is a touch high and tend towards 22 - 23mm


It's quite a few years back but you used to say the level was 22/32nds on your machinist rule which = 22.2mm

and ME 109 quipped:

28/32 isn't being too exact but 56/64" is !!
I like to set mine at 7/8"

Interesting topic carb levels.

You have a problem talking about boobies (esp. with pictures)?

I'd get the levels equal for tuning purposes on the stand. Out on the road they are going to be jumping around so much that it would take some fine and fancy statistics to tell what they are.

It occures to me that the really easy way to set very accurate levels is to determine where the top surface of the fuel is with respect to some reference on the jet stack. Then, bowl off, just hold a small glass dish under the carb, and touching it to hold steady, turn on the gas and see where the top of the fuel is with respect to your mark when the float shuts it off.

You still have a chicken and egg problem to determine where the level "should" be when the float is "correctly" adjusted. I would go by what makes your jetting work well. You can tweak the jetting by tweaking the fuel height.

What matters might be worth determining. Compute how much of a change in fuel depth will change the delivery pressure some arbitrary amount. You can look up that calculation.

Then take a guess at how much the depth changes as the fuel sloshes around.

lastly measure the depth in the bowl and with a bit of arithmetic compute the percentage change in pressure mm/mm with depth.

Compare that with your guess on the slosh pressure change to get an expected variation in pressure.

Don't sweat setting the fuel depth to a tighter tolerance that that expected variation. You're gilding a toad.

One procedure for setting the float is to run fuel into a can and lift the float with your finger until it just shuts off. Float seam should be parallel with carb bottom. This does not account for variation in float buoyancy but it's good enough and quite consistent otherwise..
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