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XR250R big bore opinions


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OK here is the deal. Been riding since I was about 10 and then I used to race hare scrambles and mostly mx here in central NH and I went OK nothing special but usually top 5 or so in amateur class local tracks. Stopped riding dirt for a while then had kids in 04 and couple years ago got a nice older 95 XR250 but didn't really start riding a lot until this year. I have always ridden 2stroke 250 mxers and lately limited experience with buddies 250 4ts. I was impressed by them but was having fun on my xr doing a bunch of dual sport stuff. Ride out of my house to different trails which can be gnarly rocky new England stuff. Really fun. The xr does this fine especially with the guys I've been riding with lately who are newer to the sport and we all have kids and mortgages. Here's the problem. I convinced one of my old racing buddies to dig out his 98 ktm250sx which he has only ripped across the lawn a couple times since about 2000-2001. He has the same situation as me with family and all. So we went to a huge sand pit this weekend and just blasted around trying to ride in a little loop for a track. You can probably see where this is going. I made the mistake of swapping bikes for a bit with him and a friend on a wr250f. I didn't realize how much I had been missing the 2 stroke snap and the general overall power. So now all I can think about is that snappy ass 2t but I realize it is not practical for my usual riding which includes a bunch of road and single track. Rarely truck it and hate to do so. So to make a short story very long... Do I have any chance of getting some power out of that XR with a 280or so kit or am I in the market for an exc300? I don't want to buy a new bike for me. My wife wants a Ttr and trying to convince 10 year old twin boys they would like riding with their parents. Not really hopeful about them but not giving up. What's an xr250 like after a big bore and lightened flywheel? Thanks and sorry for all that!

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I did a 277 kit in an 03 XR250R this summer.  Very happy with it, more bottom end.  But, as has been discussed here, if you are sticking with the stock sleeve do NOT go any bigger than 277, even that is pushing it.  BTW, in trail riding I have to push it a little, but I can keep up with my kids on their CRF450Rs.

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Just got my 03 broken in;[almost] 277 piston,xr400 baffle,gordon mods,turned down magneto,stock,rejetted carb,etc. What i difference! Was going to put a set of pedals on it from my trek mountainbike to speed it up,was so slow stock. Think i may keep it now,was thinking of getting xr400,but it just became fun to ride it!

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I did a 277 kit in an 03 XR250R this summer. Very happy with it, more bottom end. But, as has been discussed here, if you are sticking with the stock sleeve do NOT go any bigger than 277, even that is pushing it. BTW, in trail riding I have to push it a little, but I can keep up with my kids on their CRF450Rs.

Just got my 03 broken in;[almost] 277 piston,xr400 baffle,gordon mods,turned down magneto,stock,rejetted carb,etc. What i difference! Was going to put a set of pedals on it from my trek mountainbike to speed it up,was so slow stock. Think i may keep it now,was thinking of getting xr400,but it just became fun to ride it!

Yeah this is what I'm looking for. Thank you. I know I'm not going to get big hp out of it but I also didn't know if putting the money into displacement would gain enough to be worth it. I still have to be able to ride with the kids also. I am going to do a search on that thread about this. What are the down sides to this now that you guys have done it and are riding them. Does the shaved flywheel make it crisper but still good bottom? Would I be better off with a 78mm sleeve and does the jug have to be machined for it? What's the down side of going over 277 on the stock sleeve? Thanks again this is great information that I needed.

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Down side of bigger than 277 on the stock sleeve is overheating.  So far I haven't had an issue with that with 277, but even at that bore the sleeve, to me, is scary thin.  I only rode it for a couple weeks or so before I crashed pretty good and broke my collarbone, lol.  Doc says after the surgery this Thursday I'll be riding in another 6 weeks.

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I would not turn mag for trail riding,Do not go over 277 on stock sleeve too thin.

Thanks Baja. Does it lose too much bottom to make the quicker revs not worth it? I found a 78mm sleeve for around $80 do I have to bore the cylinder to make that fit and do you think the difference between 277&284 is not worth the extra trouble?

Is this the street legal version without an oil cooler?

No this is the pseudo Street legal R model with an oil cooler.

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Down side of bigger than 277 on the stock sleeve is overheating. So far I haven't had an issue with that with 277, but even at that bore the sleeve, to me, is scary thin. I only rode it for a couple weeks or so before I crashed pretty good and broke my collarbone, lol. Doc says after the surgery this Thursday I'll be riding in another 6 weeks.

That sucks hope you heal right up. My buddy I was riding with Sunday separated his shoulder too so winter is here for him now!

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For my type riding I do not like Mag or crank turned down (horse,foot trails)MC trails with big hill climbs,no run to start up.Go with 277 to start.You want to go to 300cc like ours.Want to do it right,the cost of another bike.You can bore out cases without taking bottom end apart.Yes bore Cyl.We use weld on big fin head,xr4 oil cooler,ss valves,little stiffer valve springs,ported head,34mm carb with mods,big tube header,modded big gun muffler.And more mods,cost about same as used clean 04 Wr250. Of course the Xr300 can do circles around the Wr250 on many single track trails.Stay with 277 makes a big difference.But still not fast,but fun to ride,and call it a day.Also if your bike has a zillion miles,not good to build it.

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Wow Baja, how is the reliability after all that? Is this fun to ride or just a race weapon. Do you have pictures? Love to see that thing. I don't want to go that far at all. I don't really want to change it much from what it is just some more muscle and maybe a little snappier. Anything more than that and it seems like the cost of rideability would out weigh the gains unless I went all out like yours. I would love to pick your brain sometime on those mods like the bigger cooler and proper valve springs. Do stiffer valve Springs help throttle response?

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One more thing.  There are 277 kits and there are 277 kits.  I went with the Wiseco kit because I've been using Wiseco forged pistons in bikes since the early 70s and never had a failure.  The 10.5 compression may be a little high for some folks (I think stock is 9.3), but just make sure you use premium gas if you go that route.

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Personally, I'd leave the xr alone and get a cheap 2t "buddy bike" for when the urge comes to tear some $&@! up. Older CRs and YZs are all over Craigslist for cheap. You'd have less money into a second bike in the long run, and you will keep the XR reliable.

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As far as 300cc big bores reliability we did about 10-11 of those .Im still in touch with 10 of the riders.They where done in 1997.No problems or blow ups.No over heating,all are Thumper racing low comp kits.We have one  bore and stroked 305cc zero problems.The big bores are faster then the stroker. My own 300cc about 3-4 years ago,new clutch,valves,piston rings.How many miles on it,I can only tell you this We ride almost every week 200,300 hundred miles.Some weeks 400-800 hundred miles (dirt miles) baja is real hard on bikes.I do ride different bikes every week,but by now,my Xr300 has lasted longer then any stock xr250 I ever had.Why because you dont have to ring its neck to go fast. 

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BTW, where are you in NH? I lived in Rumney (near Plymouth) back in 99/00. Hard to find anywhere to ride around there if not on a snowmobile.

I'm just down the road in Bristol. It's tough to find legal places to ride around here. The snowmobile clubs have a monopoly on the land. I quit riding because I was sick of loading driving, unloading, riding, loading blah blah blah. I got this bike so I could ride the roads and poach some trails now and then. I lent it to a friend who had to buy a bike after he gave it back. Now I'm riding again and he is getting faster all the time. Are you still in the area?

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Personally, I'd leave the xr alone and get a cheap 2t "buddy bike" for when the urge comes to tear some $&@! up. Older CRs and YZs are all over Craigslist for cheap. You'd have less money into a second bike in the long run, and you will keep the XR reliable.

I will be getting a cheap buddy bike in the spring but it's going to be for my wife and hopefully a couple for my twin boys. I don't think I am going to be able to afford a second bike for me after that kind of outlay... Plus I'm running out of garage space!

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