XR 250 build up,opinions please.

:ride: XR Ron here and hello from Panama,the land of perpetual Summer time,My 250s showing 13550 on the speedo,its not smoking or using oil,it starts very easy for a XR and its running as strong as a healthy 250 can run,ive changed the oil so many times,I could open a used oil recycling station,What I would like from you guys is your opinions on what parts or combinations of goodies to build my engine with,Here is my 2 scenarios ive put down on paper,just for a starting point,. Build #1, Full port and polish,with 3 angle valve job,change all head components as needed to up graded stuff@ guides, seals etc.hone cylinder only,and go to a 10-5-1 compression piston kit at stock 73mm bore,install stage 1 cam,all new gaskets,jet accordingly,already done full Gordons,airbox mod,stock exhaust w/welds ground,re-wind stator. Build#2 All of the above except bore out to 10-5-1 77mm piston kit,as ive heard the sleeve gets thin if bored to 78mm,and causes a heating issue,can anyone verify this?,I have a syncrowave 250 miller,tig,mig,stick welding machine with built in high frequency,so I can weld on a big fin head fin extension kit,I just havent pulled the head on my 250 yet,and when I do I want to be sure I do it all at once,because if your like me,you dont want your XR down for any time at all.I salvaged a nice oil cooler off a dead bike at my buds Moto shop,so hooking that up will be no problem,and I own a 96XR250L parts bike,so odds and ends are abundant,Ive been told by SRC that a 4mm over bore is safely enough,going past 4mm surpasses the tipping point,and although it may just work fine,Im not racing this bike,just want to build it for a good dual sport ride,with a few extra ponies to blow off all the hoards of lifan and chinese knock off bikes that are swarming around Panama.Any input from the forum will be greatly appreciated,Thank you XR Ron.:thumbsup::lol::eek::D

valve guides,springs etc

WoW!! Im so overwhelmed by all the responses,Thanks for all the help!!but anyway,since the head and cylinder will be off,Ive decided to go with the bore out,and 77mm piston kit,I mean,why not? This XR has got beau coups miles still to come,it is way far from being worn out,Ive read so much about how big a difference a 280 kit makes,Im just gonna go for it,Thanks XR Ron.

Is the bike your working on a 250L?

If so, you might want to think about getting a 250R header, and possible exhaust. Or, if you have the money, just get a full aftermarket exhaust.

Frankly, if the bike runs fine w/o any smoke or probs, there probably isn't a real need to go through all the effort, unless you really feel like you have to.

From my XR 250 days, I remember that the 280 kit is quite popular, and it should give you a new cam too. I don't know how a port and polish affects these bikes, but I know on my 650R, that if you do a port and polish, that apperently it decreases the amount of power. Something you might want to look into, if you haven't already?

XR Ron - On the subject of porting/polishing, you might take a look at http://mototuneusa.com/thanx.htm There are 4 parts on intake porting (16, 17, 18, & 19) where this guy says that he fills in his ports to make them smaller and gets more hp since the smaller ports cause the fuel to have more velocity. I'm no expert, nor am I necessarily agreeing with his fiindings, but it's definately an interesting read. He makes a decent argument.

Either way, good luck and keep us posted!

With porting you can "go backwards real fast". This is from my honda factory trained friend with 30 or so years experience who built my bike for me..

You don't change the shape of the ports - just clean them up. For instance, if you remove some metal it actually reduces intake velocity (shorter distance) - this is not a good thing. Someone who lacks experience will try to create a straight track to the intake valve and really screw things up. And the exhaust ports gets polished - but the intake ports get left with a slightly rough surface to give a little turbulence - improved fuel atomization and bottom end response.

I went with a 77mm J & E piston. Have them pop kibble white valves in while they have it apart. Don't bother having the oem valves ground - they don't have a long lifespan (older '86-'95 xr250r valves on the other hand have a very good lifespan).

jeff

Thanks for the replys, Thumpmeister its a 99XR250R, Red47403,all I plan on doing is just a basic clean up of the ports,I dont plan on hogging them out, I have also read where If its over done,It will decrease performance,Im just going to polish up the squish area,mirror finish the exhaust ports,and just touch up the intake ports,nothing crazy,just a clean up.Just how much does the 77mm over bore do for the bike?Is it worth it?That and the 1st stage cam should add about 2 HP? right? OregonRider,did it make a noticable difference? or do you guys think Im just spinning my wheels? The dam thing is running pretty good as it is.

Personally, if I were in your shoes, I would go w/ the 280 kit, a cam, filter, jetting, pipe, and so on. Leave the head alone, with the exception of the cam. You don't want to get too carried away because then you might start sacraficing what Honda built the bike for in the first place; reliability.

With those things done, you bike should go plenty well. I know when I had my 650R apart, I was thinking of doing some head work, ie. port/polish, etc. I decided not to because I didn't want to run the risk of the bike LOSING power in the long run.

Remember, this IS an air-cooled 250, it wasn't meant to be a screamer.

The stock honda cam works very, very well. I have never felt the need to go with an aftermarket one. The bike is fast because how well it pulls from bottom to top - why give up bottom end and switch to a rev cam?

I would guess the 77mm piston adds a few top end ponies. But adds more down low and mid than top - relatively...

jeff

I put the 77mm J&E piston in my 2001 XR250. What a difference! If your going to freshen the bike up a bit, put that piston in.

I already had a K&N air filter and FMF quiet pipe on the bike. It ran great, but was still, basically, an XR250.

The 77mm piston made an incredible difference. Best mod you can do.

Thats exactly why I posted this,to get a feel of other members experiences,Ive thought about it,and Im gonna leave in the stock cam,and just do a clean up of the ports,and do the 77mm piston,Im using a uni filter now,but I may switch to a K-N, Im doing a lot of street miles on this bike,I dont need to build it into a race motor,Im going to try a few less teeth on the rear sprocket,lets say a 43 or 44,theyre both available from sprocket specialists,Im running a 45 now.With the extra torque from the over bore,it should pull the smaller rear ok,I dont want to mess with the de-comp set up on this bike,changing cams means removing some parts for the de-comp,and I use it to start,and it works just fine,Ive read lots of hop up articles based on XL-XR250 4 valve head motors,and every one of them say to clean up the ports,knife cut the crank,shave weight off the flywheel, bore it, cam it, pipe it,carb it, but they were building those motors for moto-flattrack racing,all Im looking for really is a little more to pull up all these mountains,and decent cruising speed without going way radical on the build.Shes running quite well as it is,but,its only a 250 4-stroke,so I guess a little help wont hurt nothing!

I would stick with a foam filter. The stock foam filters best and is slightly more restrictive than the UNI. If you ride in alot of fine dust - I would cut the backfire screen out of the stock cage and use the stock filter. The UNI works fine - but passes more fine dust than the stocker... K & N passes dust of all varieties and clogs easily- it is not a good filter for this application.

The bike will easily pull slightly taller gearing with the new piston. I always went up one tooth on the countersprocket on my '86-'95 XR250s. For my '04 with the ohlins shock - it is taller in back now - I had to switch front and rear sprockets to get the gearing I wanted plus have swingarm clearance.

jeff

OregonRider,what gearing are you using now?Realistically,how small can I go on the rear sprocket,Im talking the max?

My first experience with a K&N filter was with my Yamaha TT350. I rode the bike stock, added the filter and rode it again. A noticable power increase was definitely there.

I have K&N filters on both my high mileage '94 XR600 and '01 XR280. Both these bikes have been used in some pretty dusty areas (Baja, UT, AZ, CA, CO). When I service the filters I use a lint free white rag to wipe the inside of the intake once the filter is off. I have never even seen a dicoloration on the rag, as the intake tracts are always spotless.

I know some people say the K&N filters pass a lot of fine dust, etc, but that has not been my experience.

I put the K&N on the XR600 when the bike was new. I have several thousand miles on the bike and it still runs as strong as ever.

OregonRider,what gearing are you using now?Realistically,how small can I go on the rear sprocket,Im talking the max?

How fast do you need to cruise at? And what kind of accelleration do you need in the lower gears. For off-road racing - I would step up to a 280 or 300 kit and drop two teeth in the rear without a problem. Actually ran better that way.

What year bike do you have and it is the south american "tornado" model? You might be limited in how small you can go and still get good clearance at the swingarm pivot.

You might need to experiment with the gearing to see what meets your needs - variety of terrain, etc.

jeff

My first experience with a K&N filter was with my Yamaha TT350. I rode the bike stock, added the filter and rode it again. A noticable power increase was definitely there.

I have K&N filters on both my high mileage '94 XR600 and '01 XR280. Both these bikes have been used in some pretty dusty areas (Baja, UT, AZ, CA, CO). When I service the filters I use a lint free white rag to wipe the inside of the intake once the filter is off. I have never even seen a dicoloration on the rag, as the intake tracts are always spotless.

I know some people say the K&N filters pass a lot of fine dust, etc, but that has not been my experience.

I put the K&N on the XR600 when the bike was new. I have several thousand miles on the bike and it still runs as strong as ever.

Here is a picture of the K & N - with the steel plate - the K & N has less usable surface area than it's foam equivalent (either stock or UNI). e.g. The foam filter has foam on the backside rather than a steel plate. The result is that it will clog quickly in extremely dusty environments - I have had friends who have had to stop and bang the dust off the filter in the middle of a race.... Sorry to be sarcastic - but for the back of the filter - where the k & n is a steel plate and the UNI and stocker have foam - the foam flows a little more air than the steel plate!

When clean, the K & N does pass air more free-ly than the foam filter - but it also passes more dirt. I have see test results that prove it - K & N versus paper versus foam - the K & N passes the most dirt. period.

jeff

HA-1312.jpg

Thanks for all the help guys, 99XR250r USA model,I want the tallest gearing it will pull,without it over stressing the motor.

Thanks for all the help guys, 99XR250r USA model,I want the tallest gearing it will pull,without it over stressing the motor.

The tallest hey, well when i purchased my 1998 XR250 it had 13/39 on it since it had been used for mainly road miles and i rode it like that for a while and found that its top speed was about 140-150km/h and that wasn't anywhere near the rev limiter it just had nothing left to give. I would say 13/42 or something similar would be a better combo. What do you want to do with it mainly? and also i don't think you can actually stress these motors much as they are bullet proof.

Matt

I'm with oregon rider and Thumpmeister. A 77mm piston kit, stock cam, cleaned up exhaust header, and proper jetting is the setup. Porting and a racing cam, while improving mid range and top end, sacrifices bottom end torque which is the 250's forte. I've had two tweaked 280s, and while they were great for flat out running, even a stock 250 was better for trailriding. I use a 48T rear steel sprocket with a 14T front and carry a 13T for tighter riding conditions. If you are riding mostly road, go to a 42T rear.

Thank You creeky,now when its back together,and the last bolt is tightened,I wont feel like I would of,could of,should of,,If any of you guys ever make it to Panama,I promise you a great time,theres so much to do here,the party boat tour is awesome,this one is not for kids if you know what I mean,XRRon dont drink no more,but who says you need to be drunk to meet girls,right,get your ass to Panama.

I read motomans article on porting,his method is dyno,and race proven,it must be right.hes getting results.

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