phbl versus vhst carb

[spark]

Hey Neo.

I was under the impression that the plain VHST and red VHST are the same bar the colour. Some people might like the racing red?

I must be honest I have not paid much attention to the OKO carbs. I was even a bit put out when I found out my Gas Gas had a Dellorto. Call me a brand whore but I grew up thinking Keihin and Mikuni were the dogs danglies. I have done some checking up though and it would appear that a lot of the parts from the OKO and PWK 28 are interchangeable so I think it's safe to assume that the OKO is a copy of the PWK 28? Anyways how do you find the build quality of your OKO, and have you had a chance to compare it to a PWK 28?

[laser1]

Interest feedback Lumpylion.

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

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

Best of balance.

Neo

A well tuned VHST on my bike made the bike better EVERYWHERE over the PHBL. It was not easy as the STD jetting recommendations were a poor choice. I read Senior Blanco's info on the VHST and contacted him via email and his suggestions were very helpful. You can get a smoother yet crisp low end (less of the pop/pop/pop surging the PHBL has on the pilot circuit) and better response everywhere else. Not so much MORE power, just very responsive and better throttle feel. I found that I had to run a rich pilot on the PHBL to produce good power. The VHST can run much leaner on the pilot and still maintain good power. (My 250 became a nice smooth running bike with a lean pilot on the PHBL, but really killed the power - felt like a 200)

For Carb cleaning, US is the way to go to REALLY get it clean. The best ones are swept frequency and has a timer. An airline works OK most of the time, but if there is trapped crud, the US can break it down and remove it. (Air line after the US to blow out the cleaning solvents)They are available on FleaBay.

[laser1]

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.

For me, The PWK 28mm is a great carb and the best setup going for the 300. Plenty of power down low. Very snappy - revs very quick. Having said that, I know some folks running a 26mm OKO and they like them very much. I dont care for the 26mm PHBL on the 300 at all. Seems OK, until you ride one with the PWK.

FWIW: in my experience, the 28mm is just alittle too much on the smaller bike(250) and is "alittle" softer down low compared to the 26mm. Has wicked over rev though.

I am convinced there are tradeoffs to every mod. so one really needs to figure out what suits there own riding style best. That usually takes time. You possibly get a great running bike and definitely REALLY fast at taking the carb off/on..

[neo]

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.

Chewy you can minimise much of this but you'll never eliminate all of it.... That's just Carburetion for you....Otherwise there'd be no reason to go Fuel Injection.

Personally I think the OKO24(soft), OKO26(intermediate), OKO28(splatterman!) is a safe bet for the money ... much cheaper to buy and tune and they have proven themselves on many occasions. But one way or the other you're not going to get perfect running every day.

These setting will get you going on an OKO or a Keihin.

110 Main jet

38 pilot

JJH needle on 3rd (middle) clip

Float level of 21 mm at 45 degrees

Thedbf,

"hard bangs instead of smooth"...is a great way to describe running a bit rich....and can happen at low or high throttle opening.

Very easily rev'd up but takes quite some time to return to idle again....is a characteristic of running lean.

Best of balance.

Neo

Edited February 12, 2011 by Neo

[neo]

Hi Spark, Red VHST are a lot more expensive. So I hope Dellorto are not charging that for the red paint.

A well tuned VHST on my bike made the bike better EVERYWHERE over the PHBL. It was not easy as the STD jetting recommendations were a poor choice. I read Senior Blanco's info on the VHST and contacted him via email and his suggestions were very helpful. You can get a smoother yet crisp low end (less of the pop/pop/pop surging the PHBL has on the pilot circuit) and better response everywhere else. Not so much MORE power, just very responsive and better throttle feel. I found that I had to run a rich pilot on the PHBL to produce good power. The VHST can run much leaner on the pilot and still maintain good power. (My 250 became a nice smooth running bike with a lean pilot on the PHBL, but really killed the power - felt like a 200)

You are the man then

Please can you share with us what your current setup is??....

Main xxx

Pilot xx

Needle xxx

Clip xnd,xrd,xth from the top

Slide xx

Mixture Screw x turns out

Fuel valve xxx

Atomiser jet xxxK

Choke xx

Atomiser height x.xmm

Needle clip nd,rd,th from bottom (needle has 5 grooves)

Gota go a buy myself one of them swept frequency US tanks ... what fluid do you use (water / methylated spirits)? ... and how long do you leave a carb in the tank for?

Best of balance.

Neo

[copemech]

For clarification to some:

The OKO carbs are basically a copy of the Kiehin PWK. I think the OKO's are produced in Tialand or something, could be wrong there. Parts directly interchange it seems, although I seem to recall hearing some issue on slides.

A budget version, the overall quality of manufacture of OKO is not as good as a Kiehin, and I think one needs to give them a good clean and inspection prior to install, as mine had some casting slag in it, but functionally, they are a good working copy at a level of build quality similar to a Dellorto I would think.

Problem with a Kiehin PWK seems trifold to me. Firstly, seems they only offer it in the 28mm version.(good for some, not for others)

Secondly, they are just more sensitive than a Dellorto PHBL, and may require more adjustment on the day.

Thirdly, they require more phisical space and can be difficult to fit on earlier Sherco models due to space limitations. A tight fit which is a bit of a pain in the butt!

OKO Carbs: Issues 2 and 3 still apply as stated above.

Good things are they are available in a range of bore sizes on the same basic casting. Add, relatively inexpensive. Seem to come set up fairly well if you get one from a decent supplier.

Bad things: Seems there is no left side bowl vent provision in the casting as with the Kiehin. I really dislike that due to the proximity of the vent on the right side to the muffler on a sherco. On a Kiehin, I can open up the left vent which assures proper venting.

[neo]

Just to add to what cope said above. ...There are also some OKO's made in China which are not good quality...

Firstly the ones I've seen do not have a Chrome slide so always ask about that prior to purchase.... Secondly they are a dull metal on the outside too....Thirdly they are sometimes half the price of the Thailand ones..... but if you wanted to get one for your Thumpster than be my guest

An OKO side will not fit in a Kiehin Carb....but a Kiehin slides will fit in an OKO (slightly loosely). The Kiehin slide is great quality and I had no negative effects when I had one in my OKO....which I no longer do.

The 30mm OKO has a vertical/elliptical opening so if you really craving power on your 290/300 it might be worth a shot.

OKO Australia has done a good job at making Kits up for each Trials bike ... might be worth taking to them if you don't mind the price.

Just remember that changing a carb is never a quick fix and it will take some degree of tuning to make it just right for you and your climate.

Best of balance.

Neo

[cabby]

Thedbf,

"hard bangs instead of smooth"...is a great way to describe running a bit rich....and can happen at low or high throttle opening.

Very easily rev'd up but takes quite some time to return to idle again....is a characteristic of running lean.

Cheers fella, I'll look out for that when out this weekend

[copemech]

Dellorto carbs:

As many others, my motto is still "the PHBL is still the best $15 carb ever produced". It just works like a AK47! I did radius the inlet a bit, not sure irf it really helps, but cannot hurt the flow transition it seems.

The standard 26mm version is a tradeoff, and there is no alt. As someone else here mentioned, I got my best results running the pilot rich, at a 38, yet leaning the fuel screw down to around 1.5-1.3/4 range(on our fuel). Sorry, but I don't buy all that BS about running them 3.5 turns out on the screw with a lean jet, screw becomes useless. Just take a look at the taper of it and the screw threads! Never lost the pinging before that either!

The low speed circuits are imperfect, as stated, yet as far as controllability goes, it seems to me that ones is just simply trying to overcome the limitations.

There seems to be a lean spot at transition to needle, or let's say off idle to about 1/8 throttle. This is based upon the "transition circuit" and is unafected by the fuel screw yet runs on the pilot jet. (the other little hole just behind the nozzle)

So basically what I am doing here is taking the pilot jet up into a range that I can really control the idle mix as best possible by getting the screw in a working range(which is also sensitive now) and getting the transition to needle to flow as best possible to accomodate the shortcomings.

Properly set, and a tad(push)on the lean side(screw), the Idle is good, and low end power smooth, and transitions well with good power, still smooth. If it gets a bit lumpy on the transition(unregulated circuit) then you have gone too far with the pilot and may need to back off a bit.

Needle in third groove down on the clip, so rich as well.

And thats all i have to say bout that!

Edited February 12, 2011 by copemech

[neo]

As many others, my motto is still "the PHBL is still the best $15 carb ever produced".

Cope I think you could make some good money here. You wouldn't get much change out of $250 for a PHBL over here.... kinda makes me feel a bit when I think of what you can get it for.

Best of balance.

Neo

[copemech]

I think I will need another batch o'beer to get into the VHST thing, later!

[spark]

Hi Neo, from what I can find the plain and red Dellorto's are the same price. Maybe you were looking at the red Dellorto with a throttle position sensor?

From Splatshop-

"Dellorto VHST 28mm Red Performance Carburettor

[neo]

From Splatshop-

"Dellorto VHST 28mm Red Performance Carburettor

[copemech]

Cope I think you could make some good money here. You wouldn't get much change out of $250 for a PHBL over here.... kinda makes me feel a bit when I think of what you can get it for.

Best of balance.

Neo

Yea, heard that, more in relation to what they cost to produce than anything! One could probably trace that basic carb back to a time when it was true!

Better than an Amal, me thinks!

[laser1]

FWIW: In my bike GG250 @ near sealevel in NewEngland (hot humid in summer)

Main 122

Pilot s34(small hole atomizer - easy to clog,but works well)

Needle d48

Clip 4th from top(top being #1) to 3rd from top(mid summer)

Slide Stock

Mixture Screw x turns out - 1 1/4 (not a static setting - WOT lean bog +1/2 turn method)

Fuel valve 300

Atomiser jet 272HH (small hole atomizer - not large hole HE)

Choke stock (60?)

Diffuser height I have the old style LOW height - the higher (7mm?)ones provide a richer midrange and run "may" better with a D37 needle and 271 HE atomizer.

This is ALL on Race Gas. If in the UK with a pump gas and tall diffuser VHST, I suggest the settings that Senior Blanco of Marlin Tec suggested and he used with on his GG250.

124

S32

D37 2T

271HE

300 valve (important)

For the US - I strip the carb and throw all the jets in clean gas for 20 minutes. (just dont want to dry out all the little orings) If I have a nasty looking carb body,(like post winter) after stripping, I put it in a water based degreaser for 20 minutes, then gas for 20 minutes - air blow out. As far as time, just dont let the carb get real hot. I find I can usually just pull the pilot jet and blow it out real well with canned air and Im usually back in business, but I do like to US the sucker every now and then to make certain its all good; For instance, like to give it the US treatment after a long dusty event. Im also very anal about the air filter. After finding a bunch of crap in my fuel petcock filter, I also check that couple times a season. (been fine so far after switch to race gas and clean can)

FWIW:I used to over oil my air filter. It didnt seem to impact the PHBL, but noticed the VHST likes to run fairly dry. (maybe part of the reason it clogs easier - but does run better) The VHST doesn't use the rubber donut that the PHBL uses and combined with the trumpeted inlet,I feel has a much higher flow than the rather ugly looking PHBL inlet. (it may be all in my head)

I had my VHST turned down to fit the stock manifold on the GG. I could swap the PHBL back and forth threw out the process to compare ridability. In the end, I preferred it, but its not night and day. Just better for me. Crisper would be the word I use. I also prefer the light return spring on the VHST.

I encourage testing. My last GG250 liked a little leaner setup. 120 main s32 pilot. I do have different reeds in this bike as well as a HC head. Also - read the VHST info on the Marlin Tec page. He has also written up a carb comparison on the TODO site. He's very knowledgeable and provides some great insight into why these carbs got a bad rep in the past. Havent seen him post here in awhile though.

Hope this helps - but remember what they say about free advise...