converting SR to R spec

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iainross

Member
Nov 12, 2001
31
0
I have just discovered why my jap import 91 KDX200SR feels very flat compared to my mates new 220, apart from 10 years development and 20 cc of course. The SR aparently has a smaller carb (28mm), different porting and a different head as well as several other changes.

Is it worth converting the engine to R spec or should I just sell it to some unsuspecting person and get an R. If it is worth sorting, what is the best way of doing this without spending too much cash. I want to keep the oil injection though as this saves a lot of f***ing about at fill ups.

So far I have stripped out the front pipe, fitted a DEP straight thru silencer and chopped the airbox lid. This has helped but there is a way to go yet.

I'm in the UK so this will affect parts availability and who I can get to do any work.

thanks

Iain
 
M

Masu

Member
Dec 29, 2001
87
0
I've got the 97 220SR, and it goes well, now. I put the Kehin PWK 35 mm carb on it, the FMF Rev pipe and it has a RSV silencer on it. Now the next thing is the Boyesen Power reeds, and a new needle for the carb.

What kind of power do you want? Low to mid grunt, or top end screaming?

If it is low to midrange grund, well the best thing that I can think of on the cheap is to drop one tooth on the front sprocket, if you like it, go back to the stock front sproket and go up 3 teeth o the rear sproket (front sprockets are cheaper rears, so start there).

Look around for that carb, it is on a lot of bikes, here is a list of bikes it works on;CRM250R RMX250R RMX250S RMX250 KDX250SR KDX250R KDX250 KDX220SR KDX220R TS200R DT200WR CR250R WR250Z

That list was supplied to me by the guy who sold me the carb I have.

Other things to condiser,

Clean your air filter ( I know I don't do mine as much as I should)
Put a new plug in there.
rebuild the top end.
New chain?

Worn or dry parts rob Hp.

Just some thoughts.

Cheers!
 
D

Dazza

Member
Jan 1, 2002
122
0
Where did you here about the different porting?Head?
I'm sure the jugs are the same with the same porting.
Mabey I am wrong.I always thought the only main differences were the
carb size 28mmPE /35mm PWK intake(oil feed ) airbox and a nut on the flywheel not a
bolt and the clutch.
 
I

iainross

Member
Nov 12, 2001
31
0
Thanks guys.
I'm riding mainly woods and trails so bottom end and mid is really what I'm after rather than a screaming top. At the moment I can only really lift the front in 1st and it won't hold 2nd on steep hills.

The sprocket is definitely a possibility but I will try to get hold of another carb. What about the manifold and the oil injection?

I read about the porting and other differences after doing a search for SRs here.

Iain
 
M

Masu

Member
Dec 29, 2001
87
0
The PWK 35 mm carb fits right into the stock intake boot, so yu retain your oiler too! The fit is tight, but just lube it and push, make sure it is in all the way around. Use a good qualily worm-gear clamp, not the piece of crap that comes with the sotck set up.

Lower gearing is the best bang for the buck I think, easy mod too, just a few bolts.

Cheers!
 
I

iainross

Member
Nov 12, 2001
31
0
I have tracked down a carb from a CRM. Just got to phone back once the owner has dug it out of his shed and checked the number and we have agreed a price. Any suggestions on jetting?

Iain
 
M

Masu

Member
Dec 29, 2001
87
0
Which PWK carb? the 35, or the 38?

Go to the Tech section at http://justkdx.dirtrider.net/ and look around, the info is there. I have a 220, so the jetting would be different, and it depends on how yor bike is set up etc. Needles are very important too!

Good Luck!
 
I

iainross

Member
Nov 12, 2001
31
0
I have got the info on the CRM carb. It is a 32mm PE carb code PE 31dahd. I checked this info with the keihin site but they only list specs and dimensions for new carbs not old ones. While this carb would probably be better than a 28mm it won't be as good as a 35mm so I will probably look elsewhere.
Any suggestions?
Since info seems to be a bit unreliable I also want to check that my carb is a 28mm. the code is PE v487fc if that means anything to you.

Iain
 
S

Steve K

Member
Jan 13, 2002
2
0
SR to R Power

I too have a '92 200SR. One thing that I haven't seen mentioned is the piston. I have rebuilt the motor twice now, and not being able to get a Jap spec. piston the first time I used a UK (R) version. Luckily I kept original. Second time I ordered a non-genuine PROX brand piston kit. This is virtually identical to original ie the port windows/skirt profile etc. Bike runs much better with the PROX piston - and they are about £30 less! Available from Grampian Motors Liverpool.
Steve.
 
I

iainross

Member
Nov 12, 2001
31
0
Thanks Steve

My piston and bore are a bit scored but I have shown them to a mechanic friend and he says they're OK. Just dress them down lightly with a bit of fine wet&dry and reassemble. I'm happy!

Iain
 
S

Steve K

Member
Jan 13, 2002
2
0
SR to R Power

Hi Iain,
Maybe I am paranoid, but after 10 years building 250 National kart engines where we service life a piston to 6hrs max I really feel you would benefit from a new one. I run my KDX pistons for a season (about 40hrs) and if my useage was harder I'd do it more often. I ride mainly in the Peak District and Wales - the thought of pushing the thing miles isn't my idea of fun! Plus I reckon that if the piston let go a new barrel/replate/rod kit looks dear. I assume you have changed the rings, at least? If not I'm sure you would notice it pulling harder.
All the best,
Steve
 
I

iainross

Member
Nov 12, 2001
31
0
Thanks for the advice Steve. It's nice to know there are others over here.

I have decided to put it together with new valves and see how it goes. If I like the result and am sure I am going to keep the bike I will do the piston and barrel in a few months time. Since the barrel is scored I don't see the point in putting in a new piston without replating. Also I've only just gone back to work after travelling down under and cash is a bit tight.

40hrs for a piston though. Thats about 6 weeks to me. I am using it reasonably gently in the lanes so I don't think it will get that much stress.

Iain
 
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mdewet

Member
Feb 14, 2008
2
0
SR to R conversion

I built a very interesting KDX. it is a 1998 frame with 1991 SR motor. First change was the piston. the SR piston is shorter, sounds wrong, but the longer skirt of the R item opens the intake port later(like the cam on a 4 stroke). the next change I made was Boysens Power reeds. Then the carb rubber of the R model, since I could only get a 39MM!!! Keihin of a KX250. Next was a FMF woods pipe with Powercore 2 silencer. This was a major challenge, as the exhaust port on the 91motor first has bolt on studs for a pipe with a flange. so off i cut the flange from the stock item, weld on a piece of tubing, and 2 lugs for springs. next opstical was the pipe curves are different. just paid huge bucks for the FMF, and it wont fit! darn!!!! make a plan I said. cut the brand new FMF on the big weld on the fat section. cut a wedge section out(10mm) heat up, bend sweat, curse, heat bend, and yes! the next was to sort overcarburetion with the 39mm monster. I coppied RB desighns divider set up and gained huge bottom end, today I am busy fitting my own version of Air Striker. I will definately let you all know how this works. This is my second KDX, and the first went very reluctantly, this one will have to be cut from my dead claws! I love my KDX. 2- strokes rule!!!!!!!!!!!!! if they stop making the oil, i will run on good old caster oil.
 
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