Pwk 38 ec 250 - 2005

[bally123]

Guys

Having refreshed my motor I have again tried and failed to get the carb set up to idle properly. Bottom line is the idle mixture screw is simply not effective. Having carefully set the slide so it is not bottomed out on the idle screw I have tried a range of jets from 38 - 45. The mixture screw makes no difference with any of them.

The closest I can get is running a 40 jet but the bike idles for maybe 10 - 15 seconds before dying. Again idle mixture screw makes no difference and the idle screw is probably too far in by this point.

So considering that the bike also displays a real richness with very slight throttle openings I am wondering if the bore of the emulsion tube is worn oversize - I think that would explain why the idle circuit is not effective as the majority of the idle mixture is coming from an excessive gap around the straight portion of the needle. This would also explain why the bike seems persistently rich at <1/8 opening. (who knows maybe it ran a bent needle in the past) (note it runs good at every other throttle opening)

I realize the emulsion tube is a pressed in, factory fit only, but does anyone know what size it should be? - better still if anyone in the UK has a spare PWK38 body they want to part with - I am up for trying to fix this, even if it means making parts and pressing them in.

Appreciate your thoughts / suggestions........

(Yes I have thought about buying a new carb but ruled that out as it's too easy)

 

[motopsycho87]

I solved that problem by using the needle in my sig otherwise you may have some top/bottom end issues...

 

[stian]

I guess you ruled out bad reeds?

 

[gassergrant]

what needle are you using, I all ways had a bad low end with the standard needle try a n3eg it sorted my bike out

 

[gray]

Pwk 38

Either your float height is to high/or dirty carb circutry. Also could be a leaking crank seals.

 

[Caravan Monster]

Allen's Performance might be worth a call. He is helpful and has been working on Mikuni and Keihins for years.

Which reeds are you running ? I find the carbon fibre type can require quite lean jetting on slow and rich on main circuits.

 

[bally123]

HI Guys,

Float height is correct, even adjusting it too be low makes no difference.
Crank is new with new seals, leak down tested fine.
Top end is new
Reeds are original Gas Gas, they have not been replaced but look mint and seal tight, no gaps, chipping or signs of wear.

Currently got a DDK needle in.

The bike has always had this issue, different needles obviously affect it but don't cure it. Spent time on it today experimenting with pilot jet,s 38,40,42,45. Now running a 45 and still same problems.

I am starting to consider a #8 throttle slide would be worth trying.

Cheers for your advice.

 

[Zman]

It is possible that your idle circuit is plugged. Can you soak the carb or run it through a ultrasonic bath to clean out its internal passages then blow air through all of them?