neo Posted October 4, 2009 Report Share Posted October 4, 2009 Hi All, After fully testing the 26mm OKO on the rocks I can safely say I will not be going back to the Keihin PWK28 again. Because on my 250 it's better all round. Combined with Boyseen Reeds it's Smoother off the bottom, more controllable and has (what seems like) just as much power as the 28mm after one third throttle. Tuning seems much more stable and less effected by climate changes. If I were competing in lower grades I'd still go for the 24mm but for me the 26mm is all-round all-better!! I thought I'd include a photo of my current family, just for good measure..... NB...the new OKOs come with an angled throttle cable tube (the tube/cap on the Keihin on this photo). Which is great but this does not unscrew like the previous carbs and the Dellorto. This may lead to cable/wire length and cable adjustment issues. I'd guess you could partly correct this by using one of those universal replace throttle wire kits. But I'm not sure how you could introduce an inline cable adjuster. If your converting from a Keihin or an older OKO just use the cap off of there. Also, watch out for that deeper bowl. as mention in the "OKO 24 Rock Test" Best of balance. Neo Quote Link to comment Share on other sites More sharing options...
copemech Posted October 5, 2009 Report Share Posted October 5, 2009 Now I am totally confused! Looks as though the one on the left says 30mm One in center says 26mm, yet looks as though the lower bowl hose(overflow) is blocked off.(is that so?) This seems to act dual function as a secondary bowl vent if I am correct(as long as the tube is run down) and without it, there is only one. And still yet not in good relation to the muff. The 26 should indeed still supply plenty of power to the motor, ala the stock Dellorto in upper range, yet still be better at mixing at lower speeds. Neo, do you have a spare metal bowl, cause I think I am about to totally screw this one up! Quote Link to comment Share on other sites More sharing options...
tony27 Posted October 5, 2009 Report Share Posted October 5, 2009 I'm guessing you've gotten your carbs from one of the scooter dealers on ebay Neo as they all seem to have either the straight up & down adjustable top or the non adjusting angled type. Oko in Oz list the adjustable 90deg top like dellorto's fitted standard have for about $35 which they reckon fit the PWK as well What sort of jetting do the carbs come with & what have you ended up running with, I'm thinking of throwing one at my bike & would appreciate a heads up on what works. What do you run from the airbox to the carb? You'd be right on the lefthand carb being 30mm Cope, I remember from one of the early posts that was the size Neo runs, would have thought it would effect the bottom end power but it doesn't sound like it does Quote Link to comment Share on other sites More sharing options...
lowbrow Posted October 5, 2009 Report Share Posted October 5, 2009 Thanks for your advice and opinions Neo. I just bought a clear floatbowl and am going to install it in time for next weekend. When you've set your floats with your handy little tool (I take it that is what the black gadget is in the photo) which of the graduations does the fuel level coincide with please, if the carb is held upright? Cheers, Dave Quote Link to comment Share on other sites More sharing options...
neo Posted October 5, 2009 Author Report Share Posted October 5, 2009 Hi Gents, Yes the one on the left is a 30mm OKO. I bought it 2 years ago. It has an elliptical bore so it the same width (opening) at the bottom as the 28mm, but 30mm high....hope that make sens. I originally went for the 30mm because they are very cheap (unusually) and the Keihin was dripping all over the shot at that time. It kinda ran OK too, until the my 250 started getting the "hunting on idle" problem. Then I swapped back to the Keihin in an effort to cure the problem. Cope I do have a spare metal bowl...but it's only an OKO (taller) one. I used the Keihin metal bowl on my 26mm to make is a looser fit. The OKO one will fit but it will rub and wear the gearbox case. You'll laugh but I a have glued and 5c piece onto the that part of my case and neither carb or case seem to be wearing now as a result. The plastic bowl is still a good option....It as low as the Keihin bowl but only wears out the pain on the case. Tony, Jetting for the 26mm is the same as the 24mm....M:112, P:38, and JJH needle (middle clip). But this time I am running Boyseen reeds.....So you may want to try a P:35 if you don't have duel stage reeds. I got this Carb 26mm Carb from the Thumpster market...the setting it came with were M:100, P:35, and JJH needle (middle clip)....if I recall correctly. Dave, thanks for reminding me about this.... I have increased the float height to 21mm (@ 45 degrees). All these Keihin's and OKO's run rich on steep descents and the idling drops as a result. With the carb installed at such a steep forward angle and the pilot jet outlet right at the front of the carb I'm convinced that 19mm is too high for a Sherco installation. This is not fully tested but I've noticed no negative effects to setting it to 21mm yet. And I the idling has not dropped on me yet. I have a couple of more things I'd like to try....Ones a GJH needle and the others a quick action throttle......But even if nothing else changes I'm gonna be a happy man for a long long time Best of balance. Neo Quote Link to comment Share on other sites More sharing options...
copemech Posted October 6, 2009 Report Share Posted October 6, 2009 So the lower (overflow tube) is not blocked off in the center one ? Quote Link to comment Share on other sites More sharing options...
neo Posted October 6, 2009 Author Report Share Posted October 6, 2009 (edited) Sorry Cope...I forgot to cover your question.... No none of the overflow tubes are blocked off...But I'm sure you can see from the Photo that the OKO's only have one high tube on the exhaust side. To cope with the heat one might need to implement my now patented "Spring Trick" ....illustrated on my Keihin photo, below. Also, Lowbrow, That black gadget is my fuel line.....Float must be set at 45 degrees ...no other method will work. Best of balance. Neo Edited October 6, 2009 by Neo Quote Link to comment Share on other sites More sharing options...
copemech Posted October 7, 2009 Report Share Posted October 7, 2009 So as things go, and if I understand correctly, Neo made TWO changes with the last test with the install of the Boyesens and the move to the 26 OKO in his findings of nervana! I am not sure which made the most noticable difference, although both come into play. And I cannot recall if he is running the stock ignition timing on the 2.5? The 26 should allow as much full power as the dellorto, which is still plenty for most! The objective here in my case being to add a more precision BUT limiting device to the more powerful 2.9. I am working on a few mods to the 24 Oko I will post up. I will run the standard bore on it at first, but other things are changing. Neo's comment on the downhill performance has been another issue with me as well. Raising the float setting (lowering the level) was well thought of, yet I admit I never did it. Makes me wonder where the actual level IS running in that clear bowl with things in place? And I am thinking mine WILL have some type of secondary bowl vent reguardless, ala the dellorto. It may get ugly! I mat totally trash this carb, but something is about to happen! Quote Link to comment Share on other sites More sharing options...
neo Posted October 7, 2009 Author Report Share Posted October 7, 2009 Hi Cope, I did run the Boyseen reeds with the Keihin 28 too....just for a few days....it was a bit smoother but not really that big a deal (to me). The effect the OKO26 has had is far more than the Boyseen Reeds. I'm running stock timing and everything else. Your OKO24 mods sound interesting.....but while your at it can you lower external drag coefficient of the carb!!!......I like my Trials bikes to cut the air as smoothly as possible Let us know how you go. Best of balance. Neo Quote Link to comment Share on other sites More sharing options...
bostit Posted October 7, 2009 Report Share Posted October 7, 2009 Neo, can you explain how you are setting the float height, 21mm measured from where? The float needle is sprung so do you compress it or with it lightly touching? I'm using a 26mm OKO and the bike seems to richen up when pointing down hill as you describe. Quote Link to comment Share on other sites More sharing options...
neo Posted October 7, 2009 Author Report Share Posted October 7, 2009 Neo, can you explain how you are setting the float height, 21mm measured from where? The float needle is sprung so do you compress it or with it lightly touching? I'm using a 26mm OKO and the bike seems to richen up when pointing down hill as you describe. Hi Bostit, This is all I can show you at the moment. But it'a pretty useless really I'll try and get some photos at the weekend and post them up. Best of balance. Neo Quote Link to comment Share on other sites More sharing options...
copemech Posted October 8, 2009 Report Share Posted October 8, 2009 Hi Cope,I did run the Boyseen reeds with the Keihin 28 too....just for a few days....it was a bit smoother but not really that big a deal (to me). The effect the OKO26 has had is far more than the Boyseen Reeds. I'm running stock timing and everything else. Your OKO24 mods sound interesting.....but while your at it can you lower external drag coefficient of the carb!!!......I like my Trials bikes to cut the air as smoothly as possible Let us know how you go. Best of balance. Neo Ok, get ready! For starters, I have reduced the frontal area to reduce the drag coefficient(CD) and rounded it a bit in an effort to porvide a more laminar airflow! Steel ball of proper size pounded into place to seal off the potential p***ing unit and other hangy down parts that are much offensive in the installation, and rub the motor case and such. Removal of the prick tube that runs up into the bowl and makes bowl instalation a pain unless you happen to be a rubik's cube guru! Screw that thing! Fooking thing is starting to look like a regular carb now, with the exception ov the totally useless fin off the tail of a '57 Chevy hanging off the back of the bowl! This may yet go! That thing and the whole little p*** jet in the inlet side are just about as useless as a dog with two dangles to me! Although I may re-use that stub with the hose on it to provide the added bowl vent tube. Looks "more" better than that straight brass pipe I extracted from the bowl! Need to do some precision drilling and get my measures straight for a good press fit, which means I need to get my number drill index from the airport this weekend, as it must be a near perfect fit. That hose will go next! All said, seems I am working from bottom -up! Quote Link to comment Share on other sites More sharing options...
copemech Posted October 8, 2009 Report Share Posted October 8, 2009 Inside Quote Link to comment Share on other sites More sharing options...
copemech Posted October 8, 2009 Report Share Posted October 8, 2009 All said to this point, I find it a bit hard to fathom why Neo has not experimented a bit with timing change, as even a minor rotation of the stator plate of 2-3mm can have some benifits in areas such as rduced kickback upon startup, less propensity for stalling, and a smoothing effect! In the balance of quickness and power, it all comes into play! Quote Link to comment Share on other sites More sharing options...
neo Posted October 8, 2009 Author Report Share Posted October 8, 2009 Hi Cope, When I had my 2002 290 I played around with the timing a lot. But what I found with the 290 was the power delivery, although softer low down, was inconsistent mid to high range. As you say the kick back on the 290 is enough to break your foot. But it's not so bad on the 250. As timing, port timing and flywheel weight are so tightly entwined I feel it's best to leave that to Sherco. And I really like the way the 250 revs up so I would not want to change that. Carbs (well OKO's anyway) are cheap and easy to work on. And have a broad range of effects on an engines performance. So that has been my primary focus to date. Well that's my story and I'm sticking to it Best of balance. Neo Quote Link to comment Share on other sites More sharing options...
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