Float Height vs. Jetting - What is really happening?

Joined
Jan 22, 2006
Messages
30
Likes
0
#1
Can someone please help me understand the physics of what changes with float height?

With a higher float height, and more gas in the bowl, does the bike run richer or leaner? Is this due to a change in pressure? Is fuel sloshing or entering jets that it would not normally enter?

I have searched the forums, and the best explanation I found was here but even in that thread there is some conflicting information.

Thanks in advance for any technical details you can provide.
 
Joined
Dec 18, 2006
Messages
8
Likes
0
#2
quintwatson said:
Can someone please help me understand the physics of what changes with float height?

With a higher float height, and more gas in the bowl, does the bike run richer or leaner? Is this due to a change in pressure? Is fuel sloshing or entering jets that it would not normally enter?
Physics? Look up "Bernoulli principle". Faster air has less pressure, so air moving through a carb throat allows the ambient air pressure in the bowl to push the gas through the carb jets.

With fuel closer to the top of a jet, the higher fuel level makes it easier for the ambient air pressure to push the fuel the rest of the way through the jet into the throat air stream, so more gas will pass through a given jet for the same throat velocity, or same throat drop in pressure. As such, a higher float height makes a motor run richer.

JayC
 
Joined
Oct 17, 2000
Messages
21
Likes
0
#3
higher flaot level requires less vacuum to deliver fuel thus richer all over big jet also richens depends on jet where it richens main is 1/2 tp full throttle while pilot is zero to 1/4 throttle and needle mainy 1/4 to 1/2