Float Level adjustments

Clark, James, Taffy et al,

Has anybody lowered the float level in an attempt to squeeze some more miles out of a tank of gas?

XR400 guys claim to extend their range ~20 miles by lowering the float 1mm w/o any impact on performance.

Just a thought



What the hell you doin' on the internet during working hours? Shouldn't you be designing some mechanical thang?


This is my last day of vaca before our 30+ day refueling outage. I'll be doing 6 - 12's.

My wrist is still real sore. There is still an appreciable lump on it. My (incompetent) Doc' would not x-ray it. I am supposed to wait another week. Unfortunately it will be two weeks before I get a weekday off. My only day next week is Saturday.

What is a person to do?


i can hardly believe that one. if it was april 1st i wouldn't answer it at all!

there are just too many variables on these bikes to take that kind of risk.



I've seen/heard this from multiple XR guys & on automotive (holley 4bbl) carbs I can lower the float level to adjust for altitude (alot easier than screwing w/jets) & help prevent sloshing over/flooding when offroad in my jeep.

Wasn't intended as an April Fool's.....


don't take it too serious brian, if you know something new i'm all ears. i just couldn't believe it that's all.

when it coughs & goes woraaa!!! etc etc what are you going to blame it on. if you do try it remember all your old settings & record them-& good luck!


Originally posted by Kevin in New Hampshire:

My wrist is still real sore. There is still an appreciable lump on it. My (incompetent) Doc' would not x-ray it. I am supposed to wait another week.

Wow, that sounds exactly like what happened to me in my last race. Does it feel sort of like a charlie horse?

An old high school buddy of mine, now an ortho surgeon, looked at it for me and said that the lump was created by swelling where the tendon had tried to yank out of the sheath that connects it to the muscle. I think. He also said that it would now be better than stock ( :)) due to reinforcing scar tissue.

It took about 3 weeks for the lump to go away but it felt about 90% normal after 2. I couldn’t test it out on the bike though since it was broken.

All you guys talkin’ about Moab really makes me want to go there myself. Maybe next time.

Meanwhile, watch the Vegas open and that MotoHed tape about fifty times. That will help take your mind off the fact that you cannot ride (well, it didn’t work for me but its worth a try).

I also read in a Dirt Bike XR test where mileage was increased significantly by changing the float height. I assume the bike spits gas out the overflow stock...

[This message has been edited by Hick (edited 10-16-2000).]


About the float level, lowering the float level is not adviseable but is an option within a very small range. Some articles talk about the effect on jetting but the change has to be miniscule.

My thoughts on an increase in mileage have NOTHING to do with improving jetting but instead reducing the OVERFLOW LOSS from the center float breather tube. Lean over your bike and it will spill from this tube first. If the float level is slightly high it will spill WHILE YOU RIDE. You wouldn't know it until you stop and then it might only be a drop or 2 because you're not bouncing any more. On Keihin PJ/PWK carbs I always route the center tube over the intake and back down. This increases my mileage noticeably and I'm careful to shut the fuel off at the end of the ride. In fear of fouling my thumper out the tube remains down in the stock configuration for now. It appears not to be dribbling out at this point.


In addition to James comments on these bikes if you are running a check valve in the gas cap vent line when the tank heats up it will pressurize the fuel going to the carb and can really exercise the overflow and blow away a lot of fuel.

On my WR I have removed the fuel tank check valve and lowered the float level about 1mm from stock and it is working great for me. On down hills I used to load up the bike but since lowering the float level problem is no longer present.


Aren't you supposed to be monitoring something?

How's the wrist?



the bike must surely have a flat spot when you hit rough going etc.

you can't have it all ways. at least if it's loading up going downhill it's probably getting enough going


over bumps

leaned over

better to have too much than too little



There are NO flat spots anywhere in the power delivery under the conditions I ride, which is everthing except motocross.


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