37 replies to this topic

[pedronicman]

has any one fitted a dellorto vhst flatslide 26mm carb to a sherco?
i am thinking of fitting one to my 03 290 to improve thottle response.

[Sirap]

Sorry, i only have information in Spanish: Marlintec, VHST in TodoTrial.com. .

Bye!!

[ILoveTrials]

Yes I have it in my sherco 2,9 2005...
a great improvement over the PHBL stock carb, indeed better than my keihin in lows (unbeatable lows), also deliivers more grunt at lows... by far the best mod i have ever made to my sherco...
the story behind this carb was very interesting..., this carb was made specifically for trials, montesa made a partnership with dellorto in order to develop a competition carb for its 315r trials bike back in 2002... however as everybody knows, this carb came as stock in 2003 gasgas pro models... for any reason, the early series of this carb came with a faulty gas valve(a craftsmanship defect..) , which is the one that controls the level of the bowl and floats, therefore it was almost impossible to get a good idle (behaves sometimes rich, and sometimes poor at idle).. thats why almost any gasgas pro 2003 user swap it for the keihin,
...so the VHST was charged with a very bad reputation among the trials community...
DellOrto figured this out and in latter series they corrected this... now it has an improved desigend valve, with a higher (bigger) valve, allowing more bowl flow...

you can read more about this in this pages... (in spanish though...)

http://miarroba.com/foros/ver.php?foroid=6...&temaid=4547056

http://www.terra.es/...ller/vhst1.html

hope this helps...

Edited by ILoveTrials, 11 May 2006 - 03:36 AM.

[copemech]

ILoveTrials,

Are you saying it is Smoother than the round slide in the Lows, or just more powerful?

[pedronicman]

message to i love trials,

how easy/hard was it to fit your vhst?
do you need a different cable and do you run the same jet size as the old carb?
by the look of the carb it seems that it should fit straight on,but what about the angled top metal cable fitting?

any help would be great as i will probably order one soon.
thanks.

[ILoveTrials]

It fits straight in (in shercos)... however the intake "neck" of this carb ie. the one that goes inside the intake manifold, should be reduced 2-3 mms for a proper fit. maybe with a special grinder or something, (I just sent it out to a metal machining place and they did it in minutes.).

The response I inmidately notice over my Keihin was a more powerful and crisp response in lows as others VHST users have noticed...,
Keihin is "flatter" in lows compared to my VHST, but in highs keihin has a highest reving due to its 28 mms bore..., however is almost unnoticeable for my riding...

hope it helps..

good luck, you wont be disappointed...

Edited by ILoveTrials, 12 May 2006 - 10:37 PM.

[ILoveTrials]

I forgot..
in todotrial forums yu can read that Paxau indeed, in his oficial workshop in spain, has fitted some shercos with the VHST.... if you want more predictable and powerfull lows this is the carb for you...
Marlintec (Jose Maria Blanco) who is a very brilliant guy with a long tradition in trials (from spain) also have compared the VHST with the Keihin and we have notice as everybody have it, a crisper, powerful, and controlable response in lows...
personally, I´ll never go back to keihin anymore...

regards..

[pedronicman]

do you need a different length throttle cable?
will the carb inlet fit ok without machining it down?

[HAM2]

'Ilovetrials' Did you keep the reed block spacer and did you keep the 05 (mellow)exhaust?
All replies welcome

[HAM2]

Pedronicman--the Marlintech page answers your questions about the inlet diameter and the cable, you just have to pick the bones out of the Spanglish text

[ILoveTrials]

I have it stock.... exhaust, cable, manifold rubber spacer, ignition timing etc... is stock.
the VHST fits straight in..you dont have to cut the trottle cable, however you have to force it in the intake manifold (apply a considerable force for the carb to pop inside!!!...)if you wont machine it.
We prefer to machine it, and not to force it because of the risk of damaging the intake manifold rubber...
Another consideration to have in mind is that you need to specify when ordering, that the carb you are needing is a 2 stroke VHST carb... this is because the VHST is used in 4 stroke also (sherco 3,2 4t, and scorpas 4t), the 4t model has the "brass diffuser" shorter, see below... this will have a modest effect at idle so you will need a larger pilot jet, the 2t model has it larger (7mm), so the pilot needs to be smaller because the carb will have more mix at idle (ventury effect).... this is explained by Jose Maria Blanco in forums and in his web page in detail... we call this part in spanish as¨"brocal", and there are a lot of guys who have machined a couple in order to find the perfect setting... it appears that the 7mm (the long one..) is the perfect match (ie. the one that comes stock in the 2t model)...

The shorter diffuser in more detail (this is the 4t configuration)...



VHST Parts in detail...


People in spain have made a couple of diffusers to compare and to figure out what is the perfect match, take a look..


Long diffuser below (this seems to be the perfect config for a 2t)....

Last picture is the one with the larger difusser (2t configuration)...

hope this helps...

Edited by ILoveTrials, 10 May 2006 - 07:22 PM.

[hugo]

ILoveTrials, on May 9 2006, 11:19 PM, said:

...so the VHST was charged with a very bad reputation among the trials community...
DellOrto figured this out and in latter series they corrected this... now it has an improved desigend valve, with a higher (bigger) valve, allowing more bowl flow...

ILovetrials:
I had fitted a Keihin on a 2.9 ’04 in the past, now would be interested in trying this VHST on a 2.9 ’06. Just need to find someone that sells them.
How would you distinguish the old ‘problematic’ models to the new, ‘improved’ ones ? Is the part# different ?

[ILoveTrials]

Ok... let me explain some important points.
Ideally, if you are going to order this carb, is better to buy it with the new upgrades... HOWEVER....My carb (and many others) is the old type VHST (Jose Marias also), that doesnt means, those are faulty carbs... the old design worked great also, only some units have a poor valve craftsmanship (in the valve that controls the inflow of gasoline to the bowl)... this can be corrected just by swapping this valve from the stock PHBL to the VHST, and it works fine... the ideal number of this valve should be from 250 to 300...
the valve that comes stock with the "old" VHST is number 200... (that is 2 mms diameter), however in extensive test made in spain, this valve seems to be very small for this model... therefore almost everybody have swapped it for the 250 that comes stock in the PHBL. the ideal number appers to be 300, as a matter of fact, in the new VHST (silver levers), it comes 300 stock!!!... this confirms that the ideal valve needs to be 300, however my VHST have the 250 that comes with the PHBL, and it runs fine whatsoever!!

This is the "old" model... the little levers that action the floats are golden brass....

This is the new model with the silver levers... take a look at the 300 valve

Edited by ILoveTrials, 12 May 2006 - 10:41 PM.

[pedronicman]

thanks 'i love trials' for all the info and pics.more than i expected!!
i am going to order one tomorrow from eurocarb
they quoted me £135+vat.
make sure you order one with the air/mixture/idle screws on the left hand side-for a sherco/gasser!!!

[pedronicman]

one last question?
on your VHST do you use the same type and size of main jet (126) and pilot (33/34)?.
in the above diagram it seems that the vhst pilot jet is very long.
cheers for the info.
pedro.