Is Eric Gorr in the House??(125 tuning)

[marcusgunby]

Eric we have covered the KTM and Cr engines fairly well over the past couple of months and we have touched on the YZ.My question is on the 02 YZ i rode it managed to pull really well under load and it had a really good wide spread of power-is this anything to do with the tapered carb or it is just sound tuning of the components ie carb/reed/port areas?The RM seems to make good power but struggles a bit under a heavy load the YZ copes with-how does the RM stack up in terms of its engine configuration?Lastly the KX has yet again got a slower engine than most what is Kawa is doing wrong-they have a big carb and yet still have no top end(and a big dip in the power at 8000rpm)i remember you saying the porting on the 2000 was better than previous years so what are they missing?Now the CR it has the least bottom of nearly any 125 ever yet it has a 36mm carb so it should benefit in pick up-where did the bottom go??Did Honda give it to Yamaha as a thanks-giving present??thanks for your time as always- Marcus:p

 

[steve125]

Wow, right now we wish Honda and Yamaha merged instead of Suzuki and Kawasaki huh Marcus!:) :p

 

[marcusgunby]

Steve I was thinking more KTM engine/Honda chassis:p

 

[David Trustrum]

I have a friend with a spare CZ engine if you have a Penton chassis sitting about.

 

[marcusgunby]

And why cant i stuff that engine in a 02 CR chassis??Service honda do something similar;) only kidding

 

[MXP1MP]

I think its a configuration setup yamaha has found the magic porting setting, is and has done everything possible to keep it that way. Same with ktm they done everything possible to keep thier bike with the killer mid/top spread it has but have been slowly working on increasing the bottom over the years. Suzuki just learned from them and applied it this year I think so it had to do with travis and that fact that it was like a "new" bike for '01. Honda and kawasaki have been trying, but I feel they are being reactive not pro active like yamaha & ktm have been. But I would love to have my YZ's motor or the KTM motor in the CR's chassis. The YZ is as close as I can get but nothing beats the CR's suspension and handling. I still love the way the aluminum frame handles especially in the whoops and how confidence inspiring it was.

 

[marcusgunby]

It sounds to me like Honda would have had a killer top end motor as the porting on the 02 is almost the same as what EG uses for pros.I think they bottled out and then downsized the inlet and exhust manifolds to try to get some bottom and ended up with nothing.They should have left the manifolds and stuck a 38mm carb on it and at least they could have boasted how it rips through the mid and top.It would be then very similar to my 01, and it would have won the shootouts easliy IMO.

 

[MXP1MP]

I think we'll see it but the bike will bare the model insigna CRF250R :p
yes I really want one ;)

 

[EricGorr]

Hi Marcus,

Theres no doubt that the YZ has the best overall package. In 2000 Kaw copied the same port shapes with minor changes to accomodate the KIPS valve. But the biggest mistake was to advance the port timing 1mm over the YZ. Yamaha hasn't struggled with reliability in the past 3 years. 1999 was probably the hottest model year 125 they ever made. But with an ignition map that was sensitive to good quality fuel, and a cylinder with narrow bridgework, hords or riders broke open their piggy banks to keep them running. But Yamaha responded to the reliability issue and improved the top end by widening the bridges, shrinking the ports, changing the head- stud pattern, and a rear port and piston pinning that should cure the reliability issues for good. The rear boost port is two narrow ports and the ring centering pin of the piston runs down the middle. Thats similar to Suzuki's design and something that I've been promoting on my 58mm pistons.

Centering the ring pin enables tuners new freedom in transfer port design. Now the rear transfer sets can be widened, re-angled, or whatever. This is common to the RM and YZ. Another thing common to these bikes is the exhaust valve design. It has two distinct functions, to reduce vary the effective stroke (distance from TDC to exhaust port opening) and the exhaust port velocity. The RM is more effective but Yamaha changed the size of the valve so when in the wide open position, the valve cleanly tucks up into the exhaust port roof, whereas the RM has a nasty sharp v-groove. While we're on that topic, the comments you make about the Kaw are clicking. The valves open at 8,000 rpm, if theres a dip in the torque curve on the dyno, its probably linked to the fact that the valve is in transition. The new KX KIPS valve is far more reliable that previous designs. Theres no more articulating flap that can break and shred the top end. Now theres 2 sliding plates, its a great idea but probably needs some tuning. I'll keep an eye on that and keep you all informed of what I find out. Regarding the porting, Kaw retarded the port timing over last years model and I'm sure all it needs is a little fiddling to suit any particular rider.

What happened to the Honda you might ask? They seemed to be on the right track last year, making significant changes to adapt their 10 year old street bike cylinder to a dirt bike. For 2002 it seems like the design team was torn over whether to make it torquey and rideable or pipey and orientated more for experts. So what they did was advance the port timing to be on par with a typical shifter kart or roadracer, then they strapped on a reed valve spacer and smaller area and longer exhaust manifold to try and get more low end. The problem is they don't work in sych. But I'm glad Honda made the manifolds available. For more low end on the 02 I'm turning down the base of the cylinder 1mm and recutting the head, stuffing the rear transfers and keeping the stock manifold. For more top end I'm grinding the upper corners of the exhaust port to allow for more blow-by past the outsides of the valves and using the 01 exhaust manifold. We did the low end mods to Rich Rohrich's 01CR125 and now his lap times are improving and he's more competitive in the tight sections like turns and whoops. Of course the R&D technicians would ask why a 5'5" 250 pound adult is riding a 125cc dirt bike when he's much better suited to velo bicycle racing or carrying safes up staircases.

The point is the manufacturers should stop trying to win the Dynojet Colored Line contest that appears in magazines every year, and start looking at the people who buy their bikes and asking them what they want. Maybe they should consider selling tuning kits that affect the powerband for a certain riding style or racing.

 

[Vic]

Originally posted by EricGorr
Of course the R&D technicians would ask why a 5'5" 250 pound adult is riding a 125cc dirt bike when he's much better suited to velo bicycle racing or carrying safes up staircases.

:confused:

 

[marcusgunby]

Thanks eric- excellent info:)

 

[Pete Payne]

I think that the yz and rm style powervalve are also way better than the cr or kx. The YZ and RM powervalve seal way better than the other 2. This will help add compression and not just speed up exh. gas velocity as the CR and KX do. This will help the YZ and RM pull better/stronger under a load. Honda & Kawasaki realy should make a better powervalve system that fits better and functions better.
Steve125 and I just got through doing some Dyno work on his o2 YZ 125 and were talking about this very issue. It is amazing how the YZ eats up the CR down low. The YZ is way more ridable and user friendly. Between the better powervalve and Ignition mapping the YZ is hard to beat.

 

[marcusgunby]

I wonder if Kawasakis are coming with port timing out of spec, i know in the past the KX cylinders were very badly cast in terms of port heights-if you put a piston into the bore and pushed it up until it hit the top of the lowest transfer-the other 3 would be of verying heights by as much as 0.5mm.

 

[NC514]

02 CR125 ignition

I was wondering, Has anyone tinkered with the CR's timing? How about a different ignition? Maybe it will give the CR something down low< or maybe i'm just totally wrong.. Any takers?

 

[steve125]

Marcus from what i understand Kawasaki back pedaled at the last minute and installed a 36mm carby instead of the 38mm on the 02 125. I just recieved team greens jetting spec for the 02's and the main jet of a 350 seems to back that up.:silly:

 

[marcusgunby]

Steve im surprised they have done that-what a bunch of wimps:mad:
NC514 i have got a WULF(FMF) ignition waiting for my 02 i will test it as soon as i get the bike but i have to sell the 01 first:(

 

[EricGorr]

Marcus, the quality of the casting on the 01&02KX125 is fairly clean and the port heights and widths seem very consistent. I've been staring at the new exhaust valve for 2 days. I see how its more reliable but I question the performance aspects. The valve is too thin to influence the effective stroke and the sharp edge exposed in the port when the valve is closed has to cause a shock wave that could show a torque trough on a dyno graph. I don't understand why Kaw doesn't employ the same type of plunger valves as Husky. I think the Patent has lapsed on that design. Another thing that Kaw could do is to change the shape of the exhaust manifold between low and high rpm. I've heard that Pro Circuit has different shaped manifolds with bushings to seal the pipe, similar to a KTM.

Marcus...Are there many guys racing Husky 125s in England? My friend Bud has one and its got the best low to mid response of any 125 I've ridden so far.


Reader notes:
Effective stroke (power-stroke from TDC to exhaust port open)

 

[Adam 982]

I work at a Kawi/Yamaha dealership and am giving some thought to getting a 02 KX125.. its gonna need some work to keep up with the other bikes ive had in the past but i think once i get stuff dialed in it should be fine.. Im 5' 10", 200lbs so i do ask alot of my 125s..

Eric or Steve.. do you guys have any Opinions on the Team Green Updates that dealers get about performance modifications on the KX's?? The more i read the specs they give, the more i thought that you could do a much better job than what they tell me to do..

(p.s. im lookin at the kawi because i know better than hopping on a Blue HandGrenade YZ125 :p )

 

[marcusgunby]

Eric thanks as always for your valuable information -i love finding the low down on the bikes-i wish someone would bring one of each brand and loads of parts to try-all for free obviously;) i cant understand why people arnt beating down my door every day:p The husky while not popular in the Uk are around.I actually owned a 2000 for a day but never rode it as the deal fell through with the sponsor.We have a couple in the AMCA chapionships and when modified they rip and rev unlike any 125 ive ever known(more like a 80 that really revs)they do very well but do tend to be the most modded bikes on the track.The low end is ive heard very strong but on the dyno ive seen in the mags it has the strangest powerband ive ever seeen, with a almost vertical climb from about 8000rpm.Then it plateaus for about 1000rpm then drops off.karl Preswood has developed pipes for the husky that really let the engine rip.Ive seen a dyno print out of a 125 that had 37.5hp ,over 30hp for 3000rpm.I know i go on about dynos alot and they arnt a true measure of how a engine performs, but in winter without being able to ride the bikes its about the only subjective way to see how a engine performs.Its a good tool to make progress though the cold winter months then back it up with testing when the weather permits,last season we had no meaningfull riding until at least March as every day was thick sticky mud:(

 

[cr-man]

Hey Eric,

How are the manufacturers getting such good low-end with these big carbs? I tried a 38mm carb on my 96 CR125 and it added top-end that's about it and I went back to stock. Your old rule use to be little carb low-end big carb top-end and that use to be the case, but the rules seem to be changing. I'm curious of your take on how the manufacturers are getting such great bottom-end torque out of these 125's with 38 and 39mm carbs?

 

[EricGorr]

Adam, I think that the Team Green specs are a good baseline and an excellent effort considering none of the other manufacturers care enough about their customers to provide helpfull tuning info. Most of the TG specs are designed for simple tools like straight porting tools and bench lathes. If I was a Kawasaki dealer mechanic and wanted to build a reputation as a tuner and race mechanic, I'd advertise the fact that I do those mods in accordance with Team Green recommendations. Get yourself a nitrogen tank and some suspension tools and soon you'll be building a stable clientell.

CR Man, I think the reason why the 38mm carbs are becoming more prevalent on production bikes is due to changes in crankcase volume and reed valves. It also has to do with advertising and machismo. Riders want to brag about the size of their carb like it has some direct connection to their riding prowess. And that same concept has parallels across the industry. For example when I go riding my 380lb 640cc KTM at an mx track, people think I'm a better rider than I actually am because I ride a huge bike, yet in reality its easier for me to ride an open bike rather than a 125. If they saw me struggle riding a 125 they'd think I was a spaz! So theres my twisted explanation of the symbolism between large bore carbs and large bore dirt bikes. Sigmund Freud is probably rolling in his grave right now:p

 

[marcusgunby]

More info on the 02 125s-i just spoke to karl prestwood who has has most of the 02s on the dyno-heres what he told me

02 Cr very poor engine 29hp but the curve was alot better than 01 with no big dips.
02 YZ good engine 32-33hp good bottom and mid top end falls of alittle.
02 KTM good all round almost identical to 01
02 KX like the Cr but even more peaky
02 RM not had one on the dyno yet.
02 Husky-right up there this year with 32hp and a very good spread of power


02CR250 was good engine-very broad power with no powervalve dip like the 01, and the exhaust was one of the hardest to improve on, like previous years.
Hope this helps but remember these all all std bikes and most can be made to run well with not too much money:)

 

[Vic]

Marcus- I'd be very interested in hearing what he has to say about the RM, when he get's one.

 

[Pete Payne]

Marcus,
The 02 cr 250 made 47.1 @ 7900 RPM on my dyno and that was all stock .The curve was very straight as you mentioned. Steve 125 and me got 33 HP out of the 02 cr 125 with some fiddling with the intake and carb.

 

[marcusgunby]

The bike Karl tested he did some mods to and got 35hp-not bad.His pipe added no top end but gained 1hp from the bottom of the midrange to just below peak.He was happy with the straight line.Once i sell my 01 i will be working with him hopefully, and my aim is big power this year-we will see.