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Setting the Float height on the Keihin PWK 28

Remove the Carburettor from the bike and clean the outer surfaces off, we use a tooth brush with a bit of the petrol from out of the carb and then blow it dry with compressed air.

Remove the float bowl, turn the carburettor upside down, remove the 2 securing screws and then gently pick the float bowl up from the back right hand side first (as you are looking down at the carb in the upside down position). You need to lift this corner up by about 5mm with the carb upside down, then the float bowl should gently come right off, be warned it isn't easy till you've got the hang of it and don't force it as you will bend the floats or the overflow pipe.

The carb needs to be tilted so the float just touches the the float valve, the float valve has a sprung loaded pin on it so if the carb is held horizontally upside down the weight of the floats will press the spring down and give you a false height. Keihin recommend that you set the floats so they are parallel with the gasket surface of the carb as shown by the 2 red lines in the picture.

The float height is critical to the way your bike runs, setting the floats further away from the Gasket surface shuts the fuel of earlier leaving the level of fuel in the float bowl lower which in turn weakens the mixture of the carb. Setting the floats closer to the gasket surface allows more petrol in to the bowl and therefore richens the mixture of the carb slightly but you risk losing more fuel out of the overflow pipe at the base of the carb. Because of this you can use the float height as a extra way of tuning your carb but to help keep things simple we recommend keeping the floats set at the same height while you get a good base setting.

We find on most trials bike the Carb is held at a downhill angle towards the engine and as such they tend to overflow eaisly so we prefer to set the floats so the top of the float lines up with the casting mark on the carburettor as shown in the picture by the 2 red arrows. Again this needs to be done with the tab on the floats just touching the float valve.
If the float height isn't right or you wish to change it, bend the tab show in the picture with a small flat bladed screw driver till the desired float height is achieved.

If you are having problems with fuel constantly poring out of the carb overflow it is likely that you have another problem, we recommend checking the float valve is clean by taking it out and giving it a good blast with compressed air or carb cleaner.

While you have the float valve out check there is no marks on the rubber tip and that the sprung loaded plunger presses in and returns easily to the same position.
On reassembling your floats make sure you have a fuel filter and it is in good condition, we recommend using these excellent Mann filters as they filter out much smaller particles than most other filters we've tried.
The overflow pipe is another part that can cause the floats to stick, when removing the float bowl it is very easy to bend the overflow pipe if the correct removal procedure is not used. When overflow pipe does get bent it can rub or catch the floats stopping them from closing the valve properly.

Some of the latest Sherco, GasGas and Beta trials bikes using the PWK have a much smaller hole in the end of the overflow pipe pictured, this helps to reduce the amount of fuel that splash's out of the overflow on these carbs. Beta did a modification piece to fit in the end of the pipe but unfortunately it isn't available at the moment but if you have access to a lathe it is easy to make one up.

Many people complain about the amount of fuel these carbs leak and they nearly all mention that the Dellorto carburettor doesn't ever leak, this is because the Dellorto PHBL, as fitted to many trials bikes, does not have a overflow pipe so if the floats stop working for some reason it will flood your engine instead. If you really want to totally stop your carburettor leaking you can block the overflow pipe off, you run a slight risk of flooding your engine when dropping your bike or parking it up at a silly angle while walking a section but we have run a bike with the overflow blocked for 5 or 6 years without problems, another bonus of blocking the overflow is the brass overflow tube that stick out of the floats can be removed making it much easier to remove the float bowls.

9 thoughts on “Setting the Float height on the Keihin PWK 28”

  • Luc Kazimirski
    Luc Kazimirski April 6, 2013 at 6:31 am

    Can you clarify the adjustment procedure for me? I've just done this three times. You say, "The carb needs to be tilted so the float just touches the the float valve." Do you mean that the tab where the float valve is attached to the float just touches the tip of the spring loaded pin? Or do you mean the point at which the float fully closes the float valve without compressing the spring-loaded pin? In your first picture it looks like the valve is fully closed but the pin has not been compressed. That is the point at which I chose to set my floats parallel to the gasket surface.
    I have been having trouble with my bike. I posted a question on Trials Central and I was directed to your page here.
    This is what I posted on TC
    "I have an almost new 2012 2.9 that is stalling on downhills. I have adjusted the float (in both directions actually, as an experiment) but that didn't help. I found the pilot to be clogged 2 times when I took the carb apart. I therefore drained the tank, put on new fuel lines and an inline filter. No help (though the jet is now staying clean). Bike runs really well otherwise. One of our local riders is trying to modify an early 2013 to put a "T" on the main fuel line. One branch will run to the carb and the other will return to the tank through a new inlet. He is wondering if this will prevent the pump from forcing too much fuel into the carb when the float should have shut off the fuel flow. Apparently the newer 2013s have this.
    Anyone have any suggestions?
    Love to know if anyone else has this problem, anyone come up with any fixes? We ride some very steep and long downhills here. It is a bit of a pain to have to think about bliping the throttle to prevent stalling when one should be focusing on brake control and survival."

    Thanks for any suggestions,
    Luc

    Reply
  • Michel

    I had a similar question. It seems that we've got it wrong, the travel point of the spring loaded pin is NOT adjustment point, rather the valve assembly movement point itself

    Reply
  • Donald

    The black plastic floats are not heavy enought to depress the float needle when held upside down.

    The old brass floats did have that problem but not the black plastic ones.


    check that out yourself if you do not believe me.

    Reply
    • chris

      The plastic floats are plenty heavy enough to depress the sprung loaded tip when the carb is held upside down, this is why you must hold the carb at a angle to check the level.

      Reply
  • […] Splat Shop - Setting the Float height on the Keihin PWK 28 / Blog might help you out just done it myself abit of trial and error Reply With Quote […]

    Reply
  • Ron

    Almost every PWK carb I have used has had the Idle Adjuster screw jammed so tight that you cant turn it.
    And because its made of black plastic. It gets rounded off. Making it even harder to adjust.
    Whats the fix and why is PWK not going anything to address this rather common problem.

    Reply
    • chris

      Hi Ron

      Yeah Keihin thread lock the plastic screw in place to prevent it moving but it does make it difficult to adjust, we sell a few different aftermarket aluminium adjusters which make adjustments easier.

      We don't work for Keihin so I can't tell you why or if they aren't working on a better solution.

      Reply
  • Ron

    I have a PWKS-38 and it is doing the same thing. My bike ran rich and was getting bad gas mileage. I finally saw gas was dripping out of the over flow. I corrected by bending tab as to lower the float level by a very small amount and now the bike is starving for gas. It is either leaking or starving I cannot find a happy medium. I have only moved the tab such small amount the adjustment cannot be that critical. GasGas 300 2-Stroke

    Reply
    • chris

      Hi Ron
      At a guess you will have had some muck suck under the float valve or the float valve has worn so it was letting a small amount of fuel to trickle through making your bike rich, then you bent the tab and it ran lean. Give the valve a good clean and while it's out check the rubber tip for any wear.

      Reply
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