Jump to content
Sign in to follow this  

Most popular 250 bigbore, 270,280,300?

Recommended Posts

Gathering parts for rebuiling my 86 xr250. I was hoping to get some input on which bore gives the best bang for the buck. Smaller than the 270 seems like a waste, 280 has a bad reliability factor while the 300 looks like more expense than it's worth. What up guys? Opinion/experience please.

Share this post


Link to post
Share on other sites

when i bought my '88 xr250 six months back it had a 77mm ,277cc kit

but it had been done 15 years ago and was long overdue a rebore,

so 78mm ,284cc was the easiest/least expensive option,

cant comment on long term reliability with the 78mm bore,but no problems

so far,however if it ever needs another rebore it will need a new liner as

its now at max bore,on a standard liner,

my mate rides a '86 250 and when we've swapped bikes the difference in

low down power is quite noticeable,so i'd definetly reccomend upping the cc's

but think i'd go for the 77mm piston as it still gives you an overbore in hand,

no experience of a 300 is that with an oversize liner or is it a longer stroke

nick

Share this post


Link to post
Share on other sites

I have put together several overbored 250s. I like the 77mm Wiseco piston, produces 277cc and leaves room for last 78mm oversize if necessary. I have overbored some to 78mm with no reliability issues. I will add that I prefer the stock cam for general purpose trail riding due to the excellent torque characteristics throughout the RPM range. I also prefer a reasonable compression ratio so that nothing more than premium pump gas is needed, the Wiseco 10.5:1 is about right. Add a pumper carb and the little 280 can be surprisingly quick.

Share this post


Link to post
Share on other sites
...280 has a bad reliability factor...
:moon:

Where did you hear that?

There isn't a true 280 kit for the 250. When people say they have a "280 kit" on their XR they are usually referring to either a 277cc kit as mentioned above or a 285cc kit. Neither one is known for reliability issues. The 277 kit uses a 77mm piston and allows for one more rebore if something goes wrong, this makes it a popular option with people. I had one myself with over 2500 miles, no issues, none. The 285 kit is the limit of the stock sleeve, one might consider it unreliable because the sleeve gets a little thin and if something goes wrong you need to resleeve.

The 300 kit is fun and makes a noticeable difference in torque, but it does seem like an expensive route for this bike. If your building a racer it might be worth it otherwise the 280 kit gives you the most bang for your buck when it comes to bore kits IMO.

Share this post


Link to post
Share on other sites

Either use a Powroll stroker crank with the 78mm piston ( Makes 300cc and I won a Gold Medal at the ISDE on one like this ) or a 300cc big bore kit. Or 300cc Big bore kit with PowRoll Stroker crank (makes 315cc, I won a Silver at ISDE on one and several Nat'l Enduro Class Championships ). When you get to 300cc it makes a big, noticable difference in torque and power. I prefer a 30mm Edelbrock Carb too.

Share this post


Link to post
Share on other sites
Either use a Powroll stroker crank with the 78mm piston ( Makes 300cc and I won a Gold Medal at the ISDE on one like this ) or a 300cc big bore kit. Or 300cc Big bore kit with PowRoll Stroker crank (makes 315cc, I won a Silver at ISDE on one and several Nat'l Enduro Class Championships ). When you get to 300cc it makes a big, noticable difference in torque and power. I prefer a 30mm Edelbrock Carb too.

I've had a couple Powroll bikes (XL175/265cc & XL350/467cc) in the past and really enjoyed them. I wouldn't put that much money in a 250 anymore. My bikes an 86 which apparently rules out the Powroll crank anyway. That 315 sounds great but the install cost would be twice what I paid for the bike. I read a couple threads here about the 78mm pistons leaving the sleeve rather thin and weak. Heard the same about XR400/440cc pistons. I love this 250 cause I can throw it around like a Schwinn. A bit more muscle would be nice though. I waste most of my $$ on the 600s. The 250 gets leftovers and hand me downs.

Share this post


Link to post
Share on other sites

Dont worry what you hear.Our 440-300s are running as long as our stockers.The trick is to bore them at 2 thousands.Then break them in easy.The biggest problem they bore the cyl out to big. Then in 6 months its blowing smoke.Also like Dwight said stock cam is best.We also run 400 oil coolers on some 250s(96-04) your 86 already has a small one if I remember.

Share this post


Link to post
Share on other sites
My bikes an 86 which apparently rules out the Powroll crank anyway.

You can stroke the 1986 up XR250 crank 3.1mm. Not much but it does make a difference. I had no problem with the 78mm bore. I haven't been riding it in many years but I still have that 300cc ISDE bike.

Dwight

Share this post


Link to post
Share on other sites
I prefer a 30mm Edelbrock Carb too.

Is there a cheaper carb you would recommend for a 280 kit? I think the Edlebrock runs around $400. I am a 38 year old novice rider who participates in the Vet class of a local harescramble series. I like the sounds of a 300 kit and Edelbrock but just not that competitive to commit so much $. I know there are a lot of posts on the matter but I would like to know what you would recommend besides the Edelbrock as a runner up. :moon:

Share this post


Link to post
Share on other sites
Is there a cheaper carb you would recommend for a 280 kit? I think the Edlebrock runs around $400. I am a 38 year old novice rider who participates in the Vet class of a local harescramble series. I like the sounds of a 300 kit and Edelbrock but just not that competitive to commit so much $. I know there are a lot of posts on the matter but I would like to know what you would recommend besides the Edelbrock as a runner up. :moon:

It's cheaper than a new bike :cheers:

Share this post


Link to post
Share on other sites

OK guys, I found a Wiseco 78mm for a great price. So 285 it is. I don't really care if it wears somewhat quicker, cylinders are easy to find and cheap. Just don't want it to blow up 50 miles from civilization. I'll be using the stock carb, had a Quicksilver and didn't really care for it. I've got a 79 XL500 pumper I'm going to oval bore and tap for a slow jet. I'll try it later down the road. What size is the stock carb? The 85 XR350 uses the same carb body but I don't know the bore on those either. From checking afermarket cam specs it appears the 250 heads don't flow as well as they could on the intake side (like all size RFVC heads). I'll be doing a bit of portwork on at least the intake. Cam will remain stock. It already revs high enough.

Share this post


Link to post
Share on other sites
What size is the stock carb? The 85 XR350 uses the same carb body but I don't know the bore on those either.I'll be doing a bit of portwork on at least the intake. Cam will remain stock. .

The stock 250 carb bore is 30mm, the 350 is 35mm. Don't go nuts on the porting, you will lose some low end snap. Port matching and light cleanup works well. I'm with Dwight, the Edelbrock is the answer.

Share this post


Link to post
Share on other sites
It's cheaper than a new bike :smirk:

Uh . . . . I only paid $525 for my bike :cheers: not far from a new bike for me. :moon:

Share this post


Link to post
Share on other sites
Uh . . . . I only paid $525 for my bike :cheers: not far from a new bike for me. :moon:

$400 for mine. It needed a seat, Supertrapp repair, tires and a kickstart lever. I had them all on the shelf. I had a 36mm Quicksilver I had already tried on the 350 but wasn't impressed. Sold it and paid for half the 250.

Share this post


Link to post
Share on other sites

Just because the bike you have is a '86 you might want to check out what has and is being done to this bike. Over the top and money most not be an issue but neat to see how a old bike can be a new bike. A friend of mine sent me the link because he thought of me and the '87 I used to have.

http://www.easterndirt.com/stories/xr250/pages/1.html

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...