xr280 question

[Lowryder1012]

What is involved in converting a XR250 to a 280. Is it as simple as just ordering a 77 mm piston & ring, pulling the cylinder and send it to a local automotive machine shop for boring? Do you need to get an oversized head gasket, or will the stock one work? What do you do for jetting changes? Anything else involved?

 

[70 marlin]

White brothers have a great kit! you'll love it!

 

[TobyS]

I did it. I got the Ross piston, JE is just as good. First I got the Wiseco piston and it weighed 10% (~30 grams) more than stock! The Ross was right on, so I switched because I was worried about balancing.\
Thumper racing has a reworked steel gasket for the oversized piston. I was told that the steel works better than fiber because it transfers heat from the head to the cylinder. That makes sense.
Looking back, I would have went for the 78 mm piston. There's enough meat in the cylinder to support it, and I figure the bore job will last a long time. Now that I think of it though, I'm not sure JE or Ross makes that size.
Hope this helps.
-Toby

 

[70 marlin]

What carb you going to run?

 

[Lowryder1012]

The stock carb. I wasn't planning to make a 2 stroke eating fire breather. I am not out to beat anyone. The bike is used for casual, but as fast as I can ride trail riding (which is about average speed). Maintaining the stock bike's ease of starting, reliability and tractability is very important to me.
The stock piston has a ton of miles and is worn out it's second set of rings. It is definately getting sloppy (it rattles until the bike warms up) and I just thought I'd try to get a bit more bottom end for a few extra bucks. I don't want to spend a fortune on this bike. (I, unfortunately don't have a fortune!) Thats why I don't just turn it over to XR's Only, or a pro shop like that. If I can't do this for a reasonable cost, I will probably just buy a stock piston (with a slight overbore,if needed, but I bet it doesn't).

 

[Garyb]

Your bike will become hard to start like the 400. My friend went to a 280 kit and now he struggles to start it.

 

[SFO]

Hey Rich, who is the big bore xr250 guy?
Can't grok his namen wish he posted more...

 

[70 marlin]

my 280 starts like a champ. even with the 33mm flat slide carb. you just need to learn the drill and what your machine wants!

 

[SFO]

I remember now, OCHSTER!

 

[DEANSFASTWAY]

Definetely use a steel gasket , They also run a bit hotter so use good oil and maybe a bigger cooler .Back in the day ny friend used to race one and it was trich he had WP forks and all . That thing he ran wide open all the time and it got so hot that it started to melt his SCOTT plastic boots. We put a 84 CR480/500 air scoop on another one and swear that it helps cool it down .

 

[VintageTech]

I have a 98 XR250 punched out to 277cc. I got the Wiseco piston and I think they also list a gasket kit for it. Check to see if Eric Gorr can get these for you. If so, send him the jug and have him bore it with piston in hand. This will assure you of good work at a reasonable price. It would also be a good idea to check the condition of your valves and their seals while you’re in there, as bad valves will negate the good of the kit.
Mine became much harder to start and felt like it had no bottom end until I went up one size on the pilot jet (stock carb). Huge difference. Turned it into a tractor. I think you’ll like it once it’s finished.

 

[Rich Rohrich]

Eric Gorr can get the piston kits and do the machine work as well. He did the bore on an XR280 engine I just finished putting together using Kibblewhite stainless steel valves.

 

[70 marlin]

DEANSFASTWAY: Where'd you folks get the WP stuff, what year bike was it? My bike came off the East Coast, Jersey area origonally? I bought it from a kid in Cleveland. Wouldn’t be funny if it was the same bike. I'm sure there's not that many 92's with WP bump sticks and a White brother's 280 kit, off the East Coast?

 

[DEANSFASTWAY]

White Bros It was a A Enduro riders bike Rob Provost. Might be the same bike . It was pretty Hammered . Im really not sure it was a 92 though. Ill have to ask him when I see him .

 

[70 marlin]

Ya my bike came pretty hammered! she's cleaned up real nice.

 

[TexKDX]

Mine starts just fine. All stock with just the usual mods - 277 piston, snorkel removed, UNI filter basket with No Toil filter, head pipe welds ground down, '98 and later XR400 baffle in the stock 250 can. I've run the gamut on jetting and have it set up pretty rich right now to keep the valves alive longer.

Stock carby.

Next time I'll put a higher compression piston in it since I ride it mostly above 7k feet.

 

[bbullet]

I have the Wiseco 284 kit, Kibblewhite valves, Hot Cams camshaft, and 34 mm Mikuni flat slide. The bike starts much easier than stock, but is a little rich right off the bottom. I love how much wider the powerband is, and it seems like it never quits pulling. I haven't sprung for a temperature type dipstick yet, but I can't really tell that it runs too much hotter than stock, but I haven't ridden that much this summer either. What is the consensus on the difference in power comparing the JE piston and the Wiseco? Would the heavier piston actually increase torque???? or decrease peak HP? hmmmm?

 

[DEANSFASTWAY]

I think its pretty much negligible . Ive weighed almost all of the 400 EX pistons and while a ROSS may be the lightest they had the heaviest wrist pin. And on the Ohaus they all were pretty close ,that was a while back but if I can dig up the info Ill post later . I always thought there might be more of an advantage/disadvavtage more consequential in a 2 stroker.

 

[70 marlin]

Bbullet: How do you have yours jetted? Mine is, main 200, pilot 35 a/s 11/4 +- a pube, clip 3rd up, needle 6DH3, slide 4.0. Your bike sounds a like its set up like mine. Except I don't have the cam or valves that you have. But I do have a XR only header and super trap megaphone SA

 

[bbullet]

I have a 6dh3 needle, 3rd clip; P-0 nozzle; 195 main; 40 pilot; air screw @ 1-1/2 out. I ran a hare scramble this weekend and the bike ran flawlessly. If the rider had only done as well as his ride, oh well. I dumped the bike 3 times and I was wondering if it was gonna be the old drill of 40 kicks. (nope)This carb is great ! 3-4 kicks and I was on my way. I could not ask for better jetting, perfect. My bike was just as fast as any bike out there. It is an extremely easy and competitive bike to ride. Give the cam a shot.

BBullet
xr 284
hot cam
kw valves
h/d springs
stage 1 porting
fmf q-pipe
mikuni tm34
uni filter
amsoil 10w-40 m/c oil

 

[70 marlin]

Thanks for the spec.’s bbullet! Who did your porting work? My bike's topend will need to be freshened up soon. So I think I'll send the head off to Al bakers XR only to have some of his magic done to it. "Porting, cam & valves"
JR rode this bike earlier this summer on a really tough trail and put it down way to many times!!!!!!! And the old girl always started very quickly!

 

[Patman]

I'm still in the process of sorting mine out as far a jetting (new brass came yesterday) but I'll say this. If you decided to freshen up the top end on your bike TALK TO RICH FIRST! The big bore he just finished putting together was mine. Eric punched it to a 284 and Rich sent the head to Kibblewhite for a complete valve job. They used a Serdi (<-- is that correct Rich?) for the machine work and put in their valves, seats, seals... (PLEASE check the actual technical issues with Rich). Rich then worked the head to match the new pieces. One word describes this engine AMAZING!. After discussing with Rich what I wanted in a finished product I bought a Thunder Alley exhaust and let the modifications begin. I'll venture that there is no other exhaust that will even come close to the TA system for the XR in both performance gains across the board and fit. It bolted up easier than the stocker. I'm trying to put together a complete write up on my new toy because it is pretty much what I consider the ultimate bike for me and think there are a lot of people that might really enjoy a reasonably low maintenance, low crash damage, good performing bike that has custom suspension setup for the rider plus all the good pieces and it costs the same or less than a showroom bike. Sort of like my own version of a KTM ;)

 

[70 marlin]

Rich would be a great sorce of info! I can't wait to read your write up! Even though my bike Has WP bump sticks front &amp; back. I day dream about stuffing the motor into a modern MX bike frame like a CR, KX or maybe a YZ? But that is just a&nbsp;fantasy.

 

[bbullet]

I had a local guy do my headwork and porting. He only does machine work on bikes and japanese cars. Fantastic work. I also had MX-Tech do the revalve and re-spring on my forks. that was a dramatic difference. I am very happy with the bike. I think the rear shock needs something, I just haven't found the cash to do what I want to it. I guess the only thing I'm not crazy about is the increased amount of stalling I am dealing with. I just can't roll as slow through the tight corners with the clutch out anymore. Other than that , my XR is 'works' in my mind!!

 

[70 marlin]

I had that problem. what I did was mess with the A/S. also I was having a small crank case venting problem of blowing oil into the air box. so it removed the vent tube from air box and added a small automotive stlye breather to it. now she has no flat spote. But I think the flat spote is just a flat slide trait? I feel a small pumper carb would be the whip!