How does float height affect engine tuning?

[crackin]

This has always interested me. Since reading several posts on this forum, it has been brought to my attention that float height is an integral part of carb tuning and actually has an effect on the performance of the engine below WOT.
I have be tuning bikes in my shed for over thirty years and I learnt by playing with things and reading plugs and i'm no tuning guru, but float height was never something i payed much attention to, apart from setting it to the specified height.
Can anyone explain to me the affects of a "too high" float setting (meaning the fuel level in the bowl is low) as opposed to a "too low" setting (meaning the fuel level in the bowl is too high) throughout the rev range?
Johno

[The Buddha]

You have to set it to the correct height. You tune everything else around that. Its not an adjustable "jet" per se.
Anyway fuel level that is too high will give you soggy acceleration upon opening throttle.
Low fuel level will act up when you're in steady throttle cruise, it would wander up and down in rpm.
That will be with 1-2 mm of difference up or down.

Past that - you will start having bigger problems, like leaking into the air box when high, or not even running and starting problems when low.

Cool.
Buddha.

[crackin]

Anyway fuel level that is too high will give you soggy acceleration upon opening throttle.

Thanks for your input Buddha
So for instance, if i was coming out of a corner and twisted the throttle and there was a slight hesitation. Would that suggest that the floats are too high regardless of RPM?
Johno

[mr72]

I wouldn't jump to conclusions about specific running conditions being related to float height per se. So and so running condition may indicate it is lean or rich. Incorrect float level can make it lean or rich, but you can't really differentiate a lean or rich condition caused by float level from it being caused by improper jetting. They work together to have one common effect.

The float along with the float needle valve is used to keep the level of fuel in the carburetor bowl reasonably constant. It's true that at the extremes incorrect float height can cause serious problems like the bike stalls under WOT (too little float height) or floods (too high). But within the range between way too low and way too high, the float height determines the volume of fuel in the float bowls which has the important effect of providing the correct fuel pressure of the fuel at the jet.

Fuel pressure affects the rate of fuel coming through the jet. More pressure = more fuel at the jet. More fuel in the float bowls will result in higher pressure at the jets, which makes it run richer in all situations. Likewise less fuel will make the pressure lower and it will run leaner.

The best way to look at it is you must first set the float height correctly and then tune mixture via jetting. But to have variant float level will make it impossible to tune mixture with jetting since you will have inconsistent and unpredictable results.

The float level is not really something you tune. It's something you set correctly to the one correct setting to ensure you can tune mixture via jets and needles. It is important to set it correctly because having it different left to right will make the mixture different on each cylinder even if the jets are the same, etc. I'd even go so far as to say that if you require grossly different pilot mixture settings on each carb, you may have a float level problem. Or if you have very different mixture side to side, check the float levels, the richer cylinder likely has a higher float. But the course of action is not to "tune" the float level, but to correct it, so the carburetor can be tuned via the ordinary means.

[The Buddha]

Anyway fuel level that is too high will give you soggy acceleration upon opening throttle.

Thanks for your input Buddha
So for instance, if i was coming out of a corner and twisted the throttle and there was a slight hesitation. Would that suggest that the floats are too high regardless of RPM?
Johno

Sorry I didn't mean to modify your post - Grrrr admin priv's.

Mr72 is correct on all counts.
In your description - I'd like to correlate it to a throttle position not rpm. Jets that are in use are dependent on throttle position. Fuel level has to be equal left to right and within 1mm of the top of the bowl, and you have to keep it there regardless of what the symptoms are.

So your question has to be re worded to get a definite answer, its like saying I've been smoking all my life but yesterday I got hit by lightning. Now, are my car tires too wore out

Cool.
Buddha.

[crackin]

Thanks for you input guys.
I pretty anal about setting my float heights, i set them with a vernier and a magnifying glass.
So it seems the consensus is set and forget and tune jets and needles etc around that, which was my original line of thinking.
Thanks again, Johno