XR 250 big bore kits
rgd...@misn.com
I have recently purchased a new XR 400 and am considering rebuilding and fixing up my old, 1988 XR
250. First, in general is it worth the cost to fix up a bike of this age? Mine is in pretty good shape but
consuming oil. I am 57 years old and mainly a trail rider. Several big bore kits are available for the bike
and if anyone has experience with them or others I would appreciate your comments. The one's I have
information are from XR's Only and from Thumper. I may have some old info on Powerol kits. The
Thumper kit lightens the flywheel. Since I am not racing I am thinking I would be better off leaving the
flywheel alone, should give me more plunking ability? Also wondering about the value of having the
suspension rebuilt by someone like Thumper or XR's Only. Any advise or suggestions on this?
Robert Shirley
rgd...@misn.com wrote:
Yup. I bought my XR250R brand new in 1987 and had the big bore to
280cc done by XRs Only in 1992. I also had the port n polish and the
3-angle valve grind. I also splurged for the 34mm flat side Mikuni
carb. and let me tell you it WAS worth it. I run the engine on the
White Bros. Megalloy setup and the bike barks and pulls harder (alot
harder) than stock. I can loft the front wheel up and over obstacles
alot easier.
As far as suspension mods I went as far as I could with stock with
revalves at both ends by Scotts and XRs Only. They can only do so
much. I ended up going UD4054 White Bros forks up front and a Works
Performance out back. With this setup I can go alot faster.
Just remember though, its a 4-stroke enduro - not a motocross bike.
But it goes 0 to stupid pretty quick for me!
Jeff Dunham
In article <4nnoom$o...@alterdial.UU.NET>, rgd...@misn.com writes:
|> I have recently purchased a new XR 400 and am considering rebuilding and fixing up my old, 1988 XR
|> 250. First, in general is it worth the cost to fix up a bike of this age? Mine is in pretty good shape but
|> consuming oil. I am 57 years old and mainly a trail rider. Several big bore kits are available for the bike
|> and if anyone has experience with them or others I would appreciate your comments. The one's I have
|> information are from XR's Only and from Thumper. I may have some old info on Powerol kits. The
|> Thumper kit lightens the flywheel. Since I am not racing I am thinking I would be better off leaving the
|> flywheel alone, should give me more plunking ability? Also wondering about the value of having the
|> suspension rebuilt by someone like Thumper or XR's Only. Any advise or suggestions on this?
Currently available you have 3 options.
- 76mm Wiseco Piston (slightly higher than claimed 10.5:1 compression)
sold by Thumper Racing, XRs Only and White Brothers.
- 76mm Arias 11:1 compression piston
sold by XRs Only and White Brothers; Not recommended by Thumper
(I agree with thumper- But I like riding tight woods...)
- 76mm Honda OEM piston from '85 XR250R - stock is 75 mm - fourth
overbore is 76mm.
I have used Wiseco's and stock honda pistons to overbore the '86-present
XR250R motor. I am currently running an XR300 kit from thumper. It is
rather expensive to install but gives the motor more power without
sacrificing the "rev-ability" of the stock XR motor. It is the
greatest bike I have *ever* ridden -> I am so thankful that
Thumper Racing went to the time and expense to develop this kit.
The other thing that will fit in the '86-present XR250R motor
is the '85 XR250R piston. The '85 had a bigger bore (75mm
versus 73mm) , shorter stroke, and slightly higher compression.
Four overbore pistons are available, the largest being 1mm over
for a total of 76mm. This is the same piston diameter as
the Thumper Racing, White Brothers, or XRs Only pistons.
XRs Only used to sell the second overbore '85 XR250R piston
as their "low compression" XR280 kit. The piston diameter
is 75.5 mm yielding a displacement of 267cc. The last time
I bought one I went for the fourth overbore piston instead.
The 4th overbore piston is 76mm for a displacement of 272cc.
Wiseco's used to be really heavy and take out the small end
of the rod very quickly on the XR250R. I purchased one from
thumper racing about 2 years ago (a 76mm piston) and installed
it in my last XR (a '94). It was only slightly heavier than
stock and worked well. Didn't rev quite as freely as the '85 XR250R
honda piston, but had great bottom end.
Do's
----
- Call thumper racing!
- Install either a stock honda piston ('85 fourth overbore) or
a wiseco from thumper.
Don't
-----
- Don't use a high compression piston (11:1) unless you want to full out
race. The Arias piston is very high compression and falls in
this category. This is the one usually pushed by XR's Only and
White Brothers (along with a cam).
- Don't go to an aftermarket cam.
- Don't go to a flat-slide carburator unless you are running in open
terrain and don't mind a loss of power off the bottom. (If you
do want one -> I have two of them with gunnar gassar throttle
assy's that I will sell -> they have been sitting in a box
in my garage for about 6 years).
I have been running with the flywheel machined down by thumper.
I was worried about stalling the bike in corners -> the owner
at thumper told me the stock flywheel is too heavy and that
I wouldn't have a problem. Also, he said he has never had
anyone complain or return one.
I have never had thumper lie to me or sell me something that
didn't work well. I can't say the same about White Brothers
and XRs Only. I will never deal with XRs Only again -> I think
that since Al Baker passed away they haven't done anything
worthwhile...
Anyway, the lightened flywheel from Thumper Racing works great
and I didn't notice any decrease in chuggability or pop-and- stall
problems that occur with four strokes that don't have enough flywheel.
jeff
--
jeff dunham Your Friendly XR Xpert
jdu...@wv.mentorg.com 1995 XR300R
(503)685-4835
Jeff Dunham
Forgot to delineate the fourth option which is the XR300
piston (80mm) that I know and love. Requires insertion
of larger cylinder sleeve and disassembly and boring
of cases.
Robert Shirley
rgd...@misn.com wrote:
>I have recently purchased a new XR 400 and am considering rebuilding and fixing up my old, 1988 XR
>250. First, in general is it worth the cost to fix up a bike of this age? Mine is in pretty good shape but
>consuming oil. I am 57 years old and mainly a trail rider. Several big bore kits are available for the bike
>and if anyone has experience with them or others I would appreciate your comments. The one's I have
>information are from XR's Only and from Thumper. I may have some old info on Powerol kits. The
>Thumper kit lightens the flywheel. Since I am not racing I am thinking I would be better off leaving the
>flywheel alone, should give me more plunking ability? Also wondering about the value of having the
>suspension rebuilt by someone like Thumper or XR's Only. Any advise or suggestions on this?
I had the 280cc bore "kit" done on my 1987 XR250R back in '92. It
included the 10.5:1 Arias pistion, 3 angle valve grind, and port and
polish. I went with the Mikuni flat side carb with the White Bros.
Megalloy pipe and oversized header and a 12-ring supertrapp.
This is a NICE motor. Pulls harder, grunts down low, a midrange hit
(well it is a 4-stroke, maybe not a hit but a good punch or perhaps a
hard slap, certainly more than a tap - oh back to the story). Its
alot easier to get the front up and over obstacles, and it'll eat most
other XR250s for breakfast without burping. I had the stock
suspension done by both XRs and Scotts Performance - while they do a
good job with the stock stuff if ya want to go faster you'll end up
going aftermarket like I did; White Bros. UD4054 forks and a Works
Performance Ultracross shock (nice shock!).
IMPULSE
Robert Shirley wrote:
Hey,
I am thinking of getting a new shock for a 93 XR 600. Can you give me a
rundown on how your ultracross works, the cost (if you don't mind) and
other mods you did to your forks.
Thanks a boingo
richard...
shu...@gmail.com
john
> I have a Aria's piston from xrs only, purchased in the 80s. Bike runs great but need to find rings. Any ideas?
>
stop by Wiseco pistons and they will hook you up.
if not go to a motorhead shop with measuring instruments and get a cross
reference.
john
gasgas ec274