50 replies to this topic

[rockyrider]

I bought a new Sherco 1 year ago, an access, it came with the vhst carb, although the owners manual only refers to the phbl. I was under the impression that if Cabby uses one, this must be the better carburetor. However, much of the reading i have done suggests the phbl can be well tuned, and may be better for a novice rider. My friends bike came with a 26 mm phbl, mine has the 28 mm vhst. We both have the 250cc models. Any comments or experience with this?

[Neo]

Me too

I bought a VHST 26 some time back and I intend to fit it to my 06 250 but in-between waiting for the new jets to arrive I did a mod on my OKO 26 which makes the tuning just prefect (lively) for me. So I'm kinda reluctant to change it and tune it now.

I rode a 2010 250 a few weeks back (which had a phbl) ... nice and soft down low but still with plenty up top too.
Some say the 2011 250 has lots of power. I noticed that it has a base cylinder gasket of 0.4mm (Standard is 1mm). So if it's power you're looking for you might want to try that simple mod first.

Thanks for starting this thread rockyrider. I hope many others join on in this one.

Best of balance.
Neo

[coriolis]

Always likes the PHBL's. Realy easy to set up, and very consistent and reliable. I think the offset of this is that they maybe dont extract as much performance from the engine as some may like, but more than enough for most.

Got the VHST on my 2011, and im not a huge fan just yet. Ive tinkered with various settings which seem to work, but then will start running lean or rich for no apparent reason.

Biggest problem i have is it runs very week between an 8th to half throttle. Ive just put a 55 slide in to richen it, which seems to have helped a little.

I think it has the potential to perform very well. Just hasnt reached it yet in my case.

Whilst on the subject, this is a very good guide to tuning: CLICK ME CLICK ME CLICK ME !!!!

I cant remember if it has already been posted on here or not, but there it is anyway!

[Thedbf]

[Neo]

coriolis, on 10 February 2011 - 08:57 PM, said:

Ive just put a 55 slide in to richen it

Hi Coriolis,
Which slide did you have in your VHST previously?... is that a 26 or a 28mm VHST?

Best of balance.
Neo

[coriolis]

Neo, on 10 February 2011 - 09:34 PM, said:

Hi Coriolis,
Which slide did you have in your VHST previously?... is that a 26 or a 28mm VHST?

Best of balance.
Neo

Its the 28mm and i think it was a 50 slide in there before hand.
Thinking about it, a 55 would weaken it over a 50.
Deffinatley wasnt hunting for fuel as much though.
Go figure !

Edited by coriolis, 10 February 2011 - 09:40 PM.

[Neo]

That right a 55 would weaken it over a 50 but what's interesting is that I've had a similar result working on an OKO26.
I had a bit of hunting but it was also a touch rich on initial throttle opening. So I ground the slide myself then adjusted the airmix richer...now things are much better.

Best of balance.
Neo

[laser1]

The VHST is a more "performance" orientated carb. Flat slide, better pilot atomizer, trumpeted intake for smoother air flow ect...However, If its not jetted correctly, or dirty, no carb will work well.

In general. the 28mm carb will have less throttle response down low than your buddies 26mm. I personally think the 250's run better with the 26's. Conversely, the 28mm will have alot more up top. (not very meaningful to a novice)

I think that there are 2 other things going for the "simple" PHBL. One is that it has been used on alot of OEM bikes (GG and Sherco) and the best jetting has been very well established. The other is that the Pilot circuit of the VHST is much easier to clog or get restricted from dirt, whereas the simplier PHBL just (seemingly) passes everything (no small atomizer holes to deal with) and also has the fuel inlet screen filter that the VHST doesnt have.

I would verify the jetting with RYP. Clean the carb (ultra sonic if you can) and put on a clean fuel filter, air filter and good gas. If you cant get the bike to run to your liking, the PHBL's are inexpensive.

I run a 26mm VHST on my 250 GG and really like it when its "clean". I need to strip it and clean it every now and then though to keep it optimized. I never did that with my PHBL. I can see why the PHBL makes a good OEM carb.

[Lumpylion]

I have a 26mm PHBL on my 2010 Sherco 2.9 and I feel that the bottom end isn't nearly as strong as bikes I've ridden with the 28mm Keihin PWK or the 28mm VHST. I'll try to launch directly after landing on the rear wheel where I won't have enough time to use the clutch to wind the motor up but often find the front end dropping.

[Neo]

Interest feedback Lumpylion.

So do you find the VHST well powered up high on your 250?

laser1, on 10 February 2011 - 11:16 PM, said:

ultra sonic if you can

You really do this?? .... and it does a better job than an Airline?


Best of balance.
Neo

[copemech]

Hummm, been waiting for this topic to come up fro a while now based upon folks experience. All basically comfirms my initial thoughts.

Am a bit surprized to see what carbs are winding up on what bikes. Seems to me that although the VHST shares most the attributes of the Kiehin carb, is is simply not as well refined. Add seems they can both be more fiddly, yet I do not find the personal desire, time or money to try to polish a VHST, in either 26 or 28 version.

All said, I did not seem to find a particular complaint in Rockyrider's post, so if it is working for him as well as anything, well just go on. If not, then I would likely just find a good phbl and put it on for the sake of (simple just works)and leave it alone.

I got a good working Phbl here in front of me, but even though I got an OKO oon the bike, I'd rather keep the Phbl than trade it off for a Vhst, because it just works!

[Spark]

Interesting topic. The main reason I am getting the Racing model Gas Gas this year is to try out the PWK 28 carb. Ohlins shock is a bonus too I must admit. Whilst I am very happy with the performance of my 300 with the PHBL carb I can't help but feel that it runs a little rich down low. I also find I use a lot of fuel relative to the other bikes but that may be more related to my riding style and the power of the bike. Although I have been reading up that the pilot circuit of the PHBL is inefficient. I am just hoping I don't get a loss of bottom end going from a 26mm bore to a 28mm bore. People describe the PWK as being smoother.... I hope that does not mean weaker. Another slight concern is having to twist the throttle further with the PWK to get the carb fully open. As it is with the PHBL I would like a faster action throttle than the white tube. I imagine with the PHBL the slide needs to open 26mm, with the PWK it would need to open 28mm. Maybe this is not true, guess I will have to wait and see. Worst comes to worst I could always machine up a faster tube out of ally.

Anyways if I am not happy with the PWK I am going to try out the VHST 26mm before resorting back to the PHBL.

[Neo]

Hi Spark,
I think you'd love the way I've tuned my OKO26 ...sounds just up your street to me

But just to add another twist to this does anyone know anything about the Racing (Red) VHST's?...How are they better (or different) and why would they only be suited to racing? I would have thought that they're not suited to trials at all but I've seen some on Trials bikes...so what's the story?

Best of balance.
Neo

[Thedbf]

This is great reading for a novice carb man like myself, but can someone tell me how you tell if your running too lean or too rich ?? Honest, I really am a novice when it comes to carb maintenance

[chewy]

Have we reached any conclusions? I'm ready to buy/try an OKO on my 2011 250 Sherco as (only intuitivly) it seems that the carburation isn't as good as it could be with th Dellorto PHBL26BS, I have followed with interest many discussions regarding Sherco carburation and fuel specifications. My bike is running as good as I can get it but it wants to stall too easily /drinks fuel and is not consitent on the bottom end of rev range either lumpy tickover (for Thedbf hard bangs instead of smooth might be a way to describe it) or dies from lack of fuel. For those of us who like to ride with tyre "hooked up",just on lean side gives snoother feel of whats going on regards grip; this is my problem when I'm looking for close control of throttle it is either too harsh or stalls too easily. Notwithstanding being fed up with paying good money for a series of problems I (like many I imagine) need to sort it out. In fairness to the bike when I go riding in Southern Europe all the sections are dry and invariably require fast response..rocky steps etc. as would the going used to develop these bikes be; the bike out of the box is idea for that. Could Neo or Copemech be persuaded to tell us/me the exact OKO setup (it would get me in the ball park as we are bound to have differentr fuel and climate conditions.