Low float level symptoms are???

So my KX250f was dripping fuel from the float overflow line which indicated low float level. Got the spec from kawasaki today, and sure enough, it was 2mm below spec. Now that I've done the adjustment, no more dripping fuel.

What I'm now curious about is what performance issues, if any, would this cause? I did have a initial hesitation that seemed to clear up by playing with the pilot, but curious what I should've been looking and listening for.



Would you please take the time to post the standard jetting from the manual?


pilot air jet

Fuels screw setting

leak jet?

needle code

needle clip position

main jet

main air jet?

What pilot jet are you using now?




I'll post up whatever specs the owners manual provides tonight. There is no service manual available yet, so I had to get the float level #'s from the Kawi technical support people (very cool guy, btw).


I just read the link posted above about FCR carb tuning, and the technique they mention for adjusting float level was different. The Kawi service page indicated that the carb should be upsidedown, perfectly level, measuring the top of the float to the top of the float bowl mating service which is what I did. But the internal spring on the needle was compressed by the weight of the float, while the link above indicates to take the measurement without the spring compressed. Did I misinterpret the instructions. If so, I'll now theoretically have a pretty lean condition which couldn't be good.

btw, I took the floats off to see if they had any leaks or fluid inside, and they seemed dry and airtight. But just the weight of the float definitely bottomed the valve out.


The procedure for setting the level on the Keihin on my XR4 is:

Holding the carb, rotate it so that the float just contacts the spring loaded end of the needle jet "without" compressing it and take the measurement at this point. Like you did, from the bowl mating surface to the bottom side of the float "in-line" with the main jet, which would be just about in the middle of the floats length, depending on your carb.

Actually, it's not a low float level condition you describe, it's a high level condition. That's why you were venting fuel out the overflow tube and getting a flooding condition. Which would make the engine seem like it's running rich. With the minimum float height measurement, the smaller the measurement, the higher the float level. The minimum height should be set at the point where the needle jet just closes off the flow of fuel into the carb from the tank, hence, setting it so the float just contacts the spring loaded end of the needle jet "without" compressing it.

With the max height setting, the larger the measurement, the lower in the bowl the float is allowed to drop.

Too big a measurement for the minimum height level could give you a lean condition at certain throttle positions and loads because your carb isn't able to keep a proper level of fuel in the bowl before the needle jet closes off.

And then there's the difference between the min. and max float height settings. If the float is allowed to drop (max setting)too much, it will tend to flop around inside the carb over rough terrain and displace fuel out the vent and up into the jets when the carbs not ready for it and cause a rich condition and possibly a stumble.

I found the factory max height setting on my XR to be overly generous and cut it back from 25mm to 19mm and fixed the stumble that XRs are known for over rough terrain.


Thanks for the detailed explanation. I had a feeling my description of float level was backwards, but at least you knew what I meant :)

I'll reread the Kawi description of whether the needle should be compressed or not, but am pretty sure they want it set with the carb perfectly upside. And when it is perfectly upsidedown, the needle is compressed. If the method you state is correct, then I'd say the level was probably close to correct in the first place, but then why would it be leaking?

Thanks again,


Results of my tinkering.

I had done the float adjustment wrong initially, thus raising the floats about 3mm too high as I took the measurement with the needle compressed. Thing is, the bike sounded real good and clean down low. I was afraid to ride it as I knew this was a lean condition, but now I wish I had.

So I pulled the carb back off and adjusted without the needle compressed, which is 6.5mm above the float bowl line. But it still leaks gas now and blubbers/pops and sounds downright ugly at low rpm's. Leaning out the air screw helped, but still rough.

Even more strange is that if I kill the engine and restart, it may actually run better or worse each time. What could that be about? I'm getting frustrated and will be bringing the carb by the shop tomorrow to have them check it over.

I'm at about 1200' above sea level, temp around 80 degrees. So according to the Kawi manual, stock jetting should be good. Also strange is that my last ride was around 3000 feet and 90 degrees (should be running rich) and it ran great?

fyi, stock jets for the KX250f are:

slow jet:40

jet needle: obeks

jet needle clip: 3

main jet:178

Any advice here would be greatly appreciated. The new bike joy is coming off my new baby :):D


Keep an eye on the spark plug while doing all this tinkering until you get it dialed in. A rich condition can foul a plug and you may be trying to dial it in on a bad plug.

I'd say if your manual tells you to set the float one way, then that's how you should probably do it for that model carb.

Be clear that when we're talking about float heights, a high float level is taken to mean with the carb right side up, not upside down like when you're setting the levels and taking measurements.

With the carb right side up on the bike, fuel enters the bowl and raises the float to a point where it closes the needle valve and shuts off fuel to the carb. If the float is set to allow it to rise too high before shutting off fuel to the carb, the level of fuel in the bowl reaches the overflow tube height and is vented out. If you can't get it to stop venting fuel and you're sure you have the level set right, then the needle valve or valve seat is bad or there's trash between the two.

This is on the KX250F right? This is a 4 stroke, right?

4 strokes have a fuel screw, not and air screw. It meters fuel, not air. So if you're adjusting it thinking it's metering air...................oops.

Sounds like you need to get some hands on help from someone local. This over the net thing is great for simple problems but it's tough to help on more difficult problems without actually being there, ya know. Hope you get it figured out.


Thanks for the terminology tips on the float level. This is new to me (never had jetting issues). I'm referring to the adjustment heights, not actual float level on the bike. So you're right that I'm trying to lower the float level, by raising the height during measurement.

The bike is a 4 stroke, but yes, it is in fact an air screw, not a fuel screw. Per the owners manual they refer to it as an air screw, and per jetting suggestions, turning it out allows more air, thus leaning it out. I was surprised to see this, as my two previous pumper carbs had fuel screws, not air screws.

I'm bringing the carb by the dealer today, and also good idea to run a new plug just to eliminate that possibility.

I'll be curious to see if my measurement, which I really believe was close, agrees with what they get.

Thanks for your help,


Don't you hate that. Just about the time we think we got jetting and the different carbs figured out, they go and change something from the norm.

The bike is a 4 stroke, but yes, it is in fact an air screw, not a fuel screw. Per the owners manual they refer to it as an air screw, and per jetting suggestions, turning it out allows more air, thus leaning it out. I was surprised to see this, as my two previous pumper carbs had fuel screws, not air screws.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now