KVF 400 Float Height

[Travis_Smith]

I have a 2002 Kawasaki Prairie KVF 400 and im trying to figure out the actual float height... i have read 17mm +- 2mm, seen 13mm and 23mm... what is happening is it will start right up, rev a little and all is fine, when it warms and you put a load on it bogs down and sputters. no i don't have a manual

[Mech]

I looked in two manuals and they bopth say 17mm +- 2mm, measured with the carb body tilted so the float is just shutting the jet off(check by blowing into the fuel fitting), and measured from the body to the highest point on the float. You can also check the fuel height with a clear plastic hose attached to the drain fitting on the bottom of the bowl. You open the drain and hold the hose up alongside the carb body and the hose fills to the level of the fuel. The fuel level should be 0.5 +- 1mm ABOVE the carb body to bowl join.

[Travis_Smith]

thanks for confirming that; I have it adjusted correctly, then. I cant get the screw loose on the bowl and i don't want to strip the screw so i cant really test the float level... I have also tried setting the fuel-air screw to no avail... i replaced the spark plug and cleaned the air filter... its a brand new carb so no clogged jets. new petcock also... is the timing adjustable?

[Mech]

I don't think the ignition timing will be adjustable.

So you have tried adjusting the idle mixture screw ? I mean, the screw goes in and out right ?

And so, when you did try it, did it start effecting the mixture if you wound the screw out(rich) and in(lean).. In other words can the idle mixture be adjusted both too rich and too lean ? Or does it just stay too rich and can't be leaned, or too lean and can't be enriched ?

And... Tell us more about how the bike behaves when it's cold, how it drives then, and also warmed up and how it drives then. Try to figure how much throttle it takes to get it to misbehave, and whether perhaps you can coax it past the bad spot by carefully working the throttle.. Load, revs, throttle opening position and speed of opening all are relevant. A good test if you can manage it is to go up a long slope/hill and then back down again, trying both runs at varying throttle settings and using different gears so you detect if it's the revs or the load that's making it misbehave..

[Travis_Smith]

It seems to me that the fuel/air mixture screw is working but it does seem to have its limit of effectiveness... i can screw it all the way in and the last 1/4 turn causes it to rev just a little... i have used the idle screw to hold the throttle open just to point it starts to sputter and then adjust the F/A screw but it doesn't seem really help it... it just seems to stay too rich...

it starts right up, but when it's cold and you give it throttle, it will just die... when it warms up and you rev it-it seems ok till you put it in gear and it starts acting up and then continues whether in gear or not... you can get about 1/4 throttle before it starts acting up and you cant throttle past it, just sputters but wont die.

[Mech]

Ok, and this is the original carb, the one that had been on it and operating ok until now right ?

I think there's two things you need to do.. They might not cure the problem but they will give us some clues about what's going on.

First off it's important to adjust the idle mixture with the throttle wound off as far as possible. If you look under the butterfly there are two tiny holes where the idle mixture gets discharged, one on each side of the butterfly when it's closed. At idle the hole near the air-filter end allows air in to chamber connecting the two holes and that air dilutes the fuel/air mixture which you are adjusting with the idle mixture screw. Once you have the mixture set right with that extra air coming in, and then start to open the throttle, the hole that had been letting air in starts to discharge the relatively rich mixture that the mixture control screw is supplying. The effect is that the mixture goes from optimum to slightly rich because the hole that was diluting the mixture is now discharging fuel/air mix instead. That has an effect similar to a accelerator pump on other carbs. If you wind the throttle opening up and adjust the mixture then you end up trying to dilute all of the fuel coming out of the two holes with the mixture screw, which doesn't really work so good(you get badly atomised fuel), and then when you start to open the throttle the mixture goes lean instead of the desired richer.  So I think you should do that first. Wind the throttle back as far as possible so it just idles, then try adjusting the mixture. If it speeds up, back the throttle off again and repeat.. Keep repeating until it starts responding to the mixture screw as it should, and it idles steadily at a low speed, and then, once the idle mixture is right at the very low throttle setting, adjust the idle speed screw so it idles at the recommended revs.

Try it like that and then if it's not reving as it should I think you should try lowering the slide needle by one notch. That's an easy job on most bikes. There's no reason why a slide needle should need changing during the normal course of events, but they can get misadjusted if people have had them apart, and the slide needle starts to control the mixture at about 1/4 throttle, so the symptom fits it needing adjusting. While you have the slide out check the diaphragm carefully for splits. You need to flex it carefully to find splits sometimes.

 

[Mech]

And..  All that advice and recommendations are based on the assumption that you've already had the carb apart and cleaned it thoroughly, with every brass jet out, and all the drillings blown out..  Also, you are sure the breather hoses on the carb and the fuel tank are on correctly and clear.. A blocked carb breather can make them flood badly..

[Travis_Smith]

This atv was a project when i bought it, it seemed to run fine but becuase the driveshaft joints needed replacing i was not able to really test the performance. The carb is brand new, the other one was also a repacement but it was missing screws and with all the trouble i decided to just replace it, but clearly that didnt help... Ill try your suggestions and see how it goes and report back.

[Mech]

Yup. Adjust the idle as I suggest then try riding it. If it still stumbles at about 1/4 throttle then try lowering the slide needle one notch. I think lowering it will be what's needed, but if I'm wrong it will hopefully make a change to show that is the part needing work.. If lowering the needle does make it worse then we will try raising it by two notches. Which ever way you move it to improve things, try moving the needle one more notch in the same direction until it starts performing badly again and then go back a notch..  The idea being to check the slide needle can go too rich and too lean, and finding the best spot.

[Gwbarm]

Good choice replacing the carb, i dont spend my time trying to repair aftermarket carbs. Just get a new one OEM is better but expensive and the last few aftermarkets i have tried have been good idle perfect runs very well through all the speeds but if you want full throttle perforce it is not there on an aftermarket carb.

[Travis_Smith]

UPDATE: took the carb out let it fill with fuel and found it was barely filling with fuel, maybe a quarter of the way. Adjusted the float and the bowl is now filling to the top... however in a purely coincidental action while testing and getting much of the same problem i had turned the handle bars while revving up and it throttled right up to wide open.... so no its down the electrical rabbit hole

[Gwbarm]

Good job getting the float height corrected hopefully that will solve your issue. When the handle bars rotated it might have pulled the throttle cable causing it to rev up, if it is an electrical malfunction from pinched wire etc on the switch it should not have revved up to wide open unless carb is misadjusted, i would think that would be a problem with the throttle cable causing that.

[Mech]

Yup, that sounds like not enough freeplay in the throttle cable..

[littleguy]

Hmm very useful info, iirc this is the same for the bayou 400