chewy Posted April 11, 2011 Report Share Posted April 11, 2011 Having bought a new 250 ST I have found it quite tricky to ride it to best of my ability. The bike is sound with some really good desighn innovations and it is generally very well put together so this is not a critique but a search for enlightenment and improvement (for me). I've been around long enough to know what I want from a bike and am well aware that I could chop this bike in for something I can manage but I'm stubborn!. The main thing I want to achieve with this bike/motor is to get it smoother, I have been through the whole gamut of carburation ,timing twistgrips reed block spacer, I've not yet thickened up the base gasket which is the next simplest/cheapest option to try. However I was pondering how to describe what I want and recalled moving from a rev 3 Beta to an Evo and the noticably smoothed out running describes exactly what I'm looking for.... I am linking this with the revised exhaust they fitted as being the main reason for this improvement. Before going down the road of fabricating a bigger volume/expansionbox which is a serious project to undertake I thought it worth seeing if anybody else has had similar thoughts or even made similar. Whilst asking questions;... titanium is obvious material choice for performance/weight but is there any spec of titanium that can be welded without a full inert atmosphere? i.e with a shrouded tig or mig system. As I would want to keep the original frontpipe to revert to, the whole front pipe can be redisigned and maybe Aluminium would be good for a prototype. Any ideas Quote Link to comment Share on other sites More sharing options...
baldilocks Posted April 11, 2011 Report Share Posted April 11, 2011 My 2011 250 came with a 35 pilot jet but the mixture screw was 4 turns out to stop it pinking so I have fitted a 36 which means I have a bit more adjustment left. I think this helps as its got more off the bottom now its not too weak. other things you could try are Boysen Reeds as they helped smooth my 290 a few years ago and are not too expensive, get the, from motomerlin assuming the design hasnt changed. first thing to do though is retard the timing as it costs nothing and can be changed back if you dont like it. I havent retarded mine as my last bike was a 300 Gasser so i'm very happy with the 250 as is but it may help you. Quote Link to comment Share on other sites More sharing options...
chewy Posted April 11, 2011 Author Report Share Posted April 11, 2011 Retarded it as much as I dare, think I've got the carburation compromise as best as possible but yes you and Copemech have reccomended Boyenson reeds I'll give Mike a call but I wanted to check out other folks experience and thoughts on the sea change in Beta running? and whether it was all simply down to the exhaust or did they rebalance the flywheels and or other mods to get it so much smoother?. Quote Link to comment Share on other sites More sharing options...
neo Posted April 11, 2011 Report Share Posted April 11, 2011 OKO24mm It's that simple ... Read up on some past posts on this. Best of balance, Neo Quote Link to comment Share on other sites More sharing options...
ormplus Posted April 11, 2011 Report Share Posted April 11, 2011 would go with maximum base gaskets,makes a big differance. Quote Link to comment Share on other sites More sharing options...
chewy Posted April 11, 2011 Author Report Share Posted April 11, 2011 OKO24mm It's that simple ... Read up on some past posts on this. Best of balance, Neo OK (o) OK (o) OKO Quote Link to comment Share on other sites More sharing options...
chewy Posted April 11, 2011 Author Report Share Posted April 11, 2011 (edited) Neo I searched for data for starting point re jets/needle etc (for OKO 24mm) and just spent 10 minutes composing a nice PM to you asking if you have any?. Your mailbox must be chocca bloc full, I'm going to try 1) carb as you suggest but prefer to tell the guy what I want. 2) Boyenson Reeds if that gives me little change 3) base gaskets. These three options are exactly in decending order of cost but I have come to conclude that PBHL carb is like several of the bits on my bike a cost compromise by Sherco and they are together cheaper than re "inventing" the exhaust system . Big thanks to all contributions. Just out of interest: I've been comparing our two bikes today, measured and compared every physical dimension including fork rake distances to footrests from bars rear wheel spindle, wheelbase etc etc last check was the bathroon scales which fully dispels any doubts folk have about weight distribution.. The Sherco is exactly the same as the Evo with rider on board, front and back (just the bike) within a kilo etc etc (All this is after/with my top yoke & shims which puts bar mounts 10mm fwd. and 10mm up). 2 degrees shallower rake angle (sherco 68 deg. Evo 66 deg) is only signifigant difference ..if I change that it will shorten wheelbase ( 1 degree reduces trail by c.25mm) , the only way to change this would involve a non reversable cut and shut of the frame in order to retain wheelbase etc so thats not going to happen to my bike although I did read somewhere that A Bert Cabastany was testing frame mods to balance the bike up. ( I take that back ..I could remake top and bottom yokes to steepen fork angle and keep wheelbase and get more lock ..drew it up this am) Edited April 12, 2011 by chewy Quote Link to comment Share on other sites More sharing options...
neo Posted April 11, 2011 Report Share Posted April 11, 2011 PM InBox now cleaned up Data... TRY THIS Best of balance. Neo Quote Link to comment Share on other sites More sharing options...
houseape1000 Posted April 11, 2011 Report Share Posted April 11, 2011 Seems to me that you're trying to turn your Sherco into an EVO.....Why bother, why not just exchange it for the bike you yearn for and save yourself all the hassle ? I thought I read on here a while back how much you liked the evo....has that changed or did you just fancy a change. Not trying to be funny, just stating what I'm thinking. Andy. Quote Link to comment Share on other sites More sharing options...
copemech Posted April 12, 2011 Report Share Posted April 12, 2011 would go with maximum base gaskets,makes a big differance. That number being three, as I was told by reputable source, that works there. Quote Link to comment Share on other sites More sharing options...
copemech Posted April 12, 2011 Report Share Posted April 12, 2011 Baldilocks, try the 38 pilot and getting the screw in an even better working range down near two turns. I had goodluck with this, yet does make them more sensitive on the day, Err towards the lean side for more smooth operation. Chewy, you are just getting out of the playing field here!!!! You have been told the basics, yet do not listen, or try things then you want to re design the exhoust! Get a grip man! Rule 1- Throttle= easy peasy! Rule 1.5- Be sure your jetting is in a working range= Cheap, easy! Rule 2- Timing= Cheap, easy , changable! Rule 3- Reeds= Cheap, easy , changable! Rule 4- Base gaskets= Moderatly labor intensive, parts cost as much as reeds probably, same to reverse. Rule 5- Carbs= Not reccommended to to complexity of setup, bigger or smaller, unless you are willing to put up with the twitchey animals. They are only a slight bit smoother than a well set reliable Dellorto. Having ridden a few 250 Betas over the years, in my mind they are just more a torque set motor and mostly flat as a pancake. I have doubts one would ever get the same out of a Sherco, as they seem more perky in the mid and top range, on average, and thus in the transitions. There is a LONG header pipe for the Sherco from '05, as far as I know they still fit, but that would need to be verified. They cost more than an OKO! Yet cheaper than TI! Quote Link to comment Share on other sites More sharing options...
copemech Posted April 12, 2011 Report Share Posted April 12, 2011 Most dealers would probably give away theri collection of #30 pilots! Quote Link to comment Share on other sites More sharing options...
neo Posted April 12, 2011 Report Share Posted April 12, 2011 Personally guys I think that messing around with the ignition or port timing to this degrees gives some unpredictable performance characteristics and side effects. I also think it's a shame to lift the pot on such a new engine. And with this goal I think the Boyenson Reeds are a waste of time .... I actually got more power (not less) when I fitted mine. Leave that nice new engine alone. Just fit the 24mm OKO. It's not expensive, it requires no special tools (puller or torque wrench), it's easily removed and it's easily resold. Best of balance. Neo Quote Link to comment Share on other sites More sharing options...
chewy Posted April 12, 2011 Author Report Share Posted April 12, 2011 You're all right.... its this retirement thing as cope said before ."just got to fiddle" I am now trying to order 24 mmm oko with following innards DATA as supplied by Neo (current settings....M:112, P:138, and JJH needle (middle clip) then slapped it on there using the slide (and JJH) from the Keihin, which went straight in) I assume that the general concencus of opinion is that following Bernouli and his equation (to get same amount of fluid through a smaller apeture it will have to flow faster, I'm not sure if gas/air mix counts as a fluid?) we go with smaller bore and the metering (throttle adjustment) is more profound/noticed by the engine. Re houseapes comments yes you're right fancied a change and/but( great grammar that) I am now overbiked/finding the Sherco a handfull and have to live with it until depreciation "hit" is "normal" unless I can get to ride it properly in which case it will last a damm site longer than the Evo and be better value for money. Yes I like the Evo.... Still got one but they have thier foibles also. If anybody can suggest what "spare" jets to order at the same time to give me a bit of adjustment for fuel /altitude variations ( fiddling is a way of life.. I can't help it I spent 45 years as a mechanical engineer). I.d be gratefull and able to add my info from experiences to the "databank" herein. Thanks guys for keeping me on the straight and narrow, will keep you posted . Quote Link to comment Share on other sites More sharing options...
mikee Posted April 12, 2011 Report Share Posted April 12, 2011 I've had a ride on a new 2011 290 and found that it was a lot smoother than the 250. Weather it was just setup better i don't know,but it was a lot better off the bottom end than the 250. Not saying go and buy a 290, but find someone who has one and have a go.. Quote Link to comment Share on other sites More sharing options...
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