Sherco 290 - what carb is this?

[Somkid]

Hi, I've just bought my first trials bike, I think its a Sherco 290 2003 Model, I cant get it to rev out unless I completely remove the air cleaner element.. I have a brand new element in there so that's not the issue, so most obvious is jetting. I've read the various posts on what others use and also read the Sherco USA PDF's on jetting.

However, the bike has a Mikuni carb on it -  does not look like any described on here as being the usual or factory options, i.e. its not a Keihin PWK.  I could buy a Keihin PWK (28mm?) here or a chinese copy easily enough.  Before I do that though - does anyone recognize this carb? I'm in Thailand and maybe in Asia this was an original item and all I need to do is play with the jetting.  This carb measures 45mm Ext Air side, 35mm Ext Manifold, 80mm width and about 130mm height. 

Any thoughts much appreciated

Btw, if you come to Northern Thailand, you can ride the mountains and jungles here, no one minds, the police don't even stop you on the roads, I have enduro bikes as well.

Edited April 7, 2021 by Somkid
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[totty79]

Looks like a VM, I have a VM26 on another bike that looks identical to it.

I can't remember if the pipe at the base that looks like it's plugged is an overflow/breather or a drain connected the the screw that's near it, either way it shouldn't need to be plugged and may indicate that the float height is set wrong. The string pull on the choke may also be a problem, it might not be closing fully. I'd see how it runs after sorting out those two things.

[Somkid]

Thanks Tony, I will check those. Guess I'm really trying to find out if this carb was original on the bike and rather than waste time trying to make this one work, just install the one it should have.. 

Despite searching various sites I can't get a definitive on what it had from the factory 

 

[b40rt]

What position is the clip on the needle ? 

[pauls320]

Oem carb is dellorto  PHBL26BS

[Somkid]

Thanks for the replies, I've tried needle in highest slot but makes little difference. The needle is 'fat' with little or no taper and no pointed end, it does not even start to go into the main jet itself (Mikuni are very short though) so it must only be working in the jet tube itself.  

As it was like this when I bought it and I have no idea what it should run like, Im in the dark a little. it starts ok, idles but not really smooth and runs in mid range but open throttle too far and it splutters and wont rev out, if I remove filter (new and both parts of exhaust cleaned and repacked) then it revs ok.  Throughout the range its definitely not as strong or responsive as my friends 2003 Scorpa 250.

Hard to source a Delorto carb here - thinking I will risk a tenner on a PWK 28 chinese copy, I have two Yamahas WR200 / DT200 that run these and they work fine - but they are more 2T powerband bikes with expansion chambers so not that relevant.  I dont want to go bigger than a 28 as cant easily source a bigger manifold.

[totty79]

I've used a couple of Chinese copies on road bikes including a PWK 28, and they weren't all that bad but I never really got them running as well throughout the range as I did with a genuine, and on a trials bike this will be more noticeable.

If you know the correct jets for a PWK 28 then for the sake of a tenner the copy might be worth a try. The current carb is much better quality though so if you're going to need to spend a lot of time on jetting then it may be a better starting point.

[Somkid]

I've ordered a vm car jet kit with various pilot and main jets, I know how to diagnose rich and lean on a 2T so I'll stop assuming it's some other problem and that it just never ran properly with this vm carb and current jets on it!  If no result I'll try one of my cheapo 28m PWKs.