Beta Keihin Pwk28 Fuel Starvation Fix

[redhubuk]

Just like to share these mods that I've done to my Beta Evo Keihin PWK28 carb's.
This was an attempt to stop the carb running out of fuel during steep or long climbs, If it was preceeded by a sharp drop,
it was even worse. There are reports that the same thing happens to these Keihin carbs on the KTM Freeride's.

The following mods seem a bit and#39;last resort' so always check the simple stuff first, like float levels, clear breather hoses,
particularry on the Evo's where one pipe runs up the frame towards the petrol cap. This can easily get blocked with mud or water
or filled up from a jetwash.

 

Disclaimer- I'm not saying these mods will be a cure all for everyone but I found on the ones I've modded this has cured my problems.
I've tried to do the mods in order of importance, and feel the #1 and #2 steps are most worthy. You maybe able to get away without
having to dismantle the body of the carb for #2 mods, but all of it is at you own risk, this is a guide not an instruction

.

Why? My views are this, the PWK28 was and still is a mighty fine piece of engineering, but it's been around along time.
I'm thinking that Keihin have not refreshed their die-casting tools or broaches for many years, subsequently everything is wearing out
small gaps are becoming too narrow, pocket depths are getting shorter/larger/smaller, cheaper alloys are used with less stability etc.
even lookng at the quality of the slide chamber broaching, it is a ploughed field now.

 

So my aim here was to free up space around the main jet to make sure it can always fill, even with the jaunty angle the carbs installed
on the Beta's, and to open up the holes in the main jet roof too allow any air pockets out and reduce the time to fill this void after a decent.
It's all about fuel flow around the main jet.

 

Enjoy

 

Keihin PWK Mods.pdf

[joe_300]

Instead of screwing around with these small volume adding cuts. why dont you just get one of these that will actually add volume? Made by Trun Racing in Italy. This is where all the top riders like raga, casales, ferrer, cabes get them.

Edited October 29, 2015 by joe_300

[lineaway]

It`s actually a venting problem. http://www.trialscentral.com/forums/topic/41033-kehin-pwk28-drain-bolt/?hl=keihin vent added

[thesolidman1]

Just like to share these mods that I've done to my Beta Evo Keihin PWK28 carb's.

This was an attempt to stop the carb running out of fuel during steep or long climbs, If it was preceeded by a sharp drop,

it was even worse. There are reports that the same thing happens to these Keihin carbs on the KTM Freeride's.

The following mods seem a bit and#39;last resort' so always check the simple stuff first, like float levels, clear breather hoses,

particularry on the Evo's where one pipe runs up the frame towards the petrol cap. This can easily get blocked with mud or water

or filled up from a jetwash.

 

Thanks for sharing what you have learned and your effort with the pdf instructions, interesting.

[dan williams]

Main jet tower is in the center of the float bowl to make it relatively insensitive to acceleration/deceleration. The float center of buoyancy is also centered along the side axis of the carb for the same reason. This helps with the angle of the carb as well but it's not the main reason as most designs are really throw backs to street bike design. I've often thought it would be fun to design an actual "trials" carb. Something that was completely insensitive to angle. It looks to me that these mods actually are intended to help with issues caused by fuel aeration.

[billyt]

 "I've often thought it would be fun to design an actual "trials" carb"

 

  Dan.    it is supposed to be all top secret.

 

BillyT

[jml]

I've been having the same problem with 2010 Beta Evo, I've still yet to fix the issue as I rarely get to ride at the place which causes the issue (very steep grippy sections). I'm still unsure if it's a flooding or a starvation issue so I just recently ordered a PWK28 clear float bowl  . Next time I'm riding on the steep stuff I'll first try bringing up the idle and see if that fixes it, I'm worried that the overflow pipe in the float bowl might be fouling the floats. If that fails I'll throw on the new clear float bowl and see if it's a flood/starvation condition and go from there. That or just get a 2016 Evo