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Making a 2003 CR250 more trail-worthy

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I just swapped a Yamaha Warrior for a 2003 CR250. My riding preference is enduro/trail riding (more technical over fast), and not MX. Without any major engine work or breaking the bank, what is the best bang for the buck to make this bike suit my riding style (flywheel weight, gearing, etc.)? What tuning of the engine itself can be done? It has a full FMF exhaust, but is otherwise stock.

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I bought a 03 cr250 built for the woods. I haven't done anything to it but it was close to everything I wanted suspension on a mx bike sucks in the woods. The bike had the suspension revalved and it's amazing. I also have a rekluse but that isn't a must. Also larger tank, rotor and pegs. There is one thing I want to do is a pwk air striker carb. I really like my bikes jetted well and the tmx mikuni sucks. So if I were to build a cr250 for the woods, suspension and carb would be #1. I also have a turbine core for a silencer. Spark arrestor is a must for most areas I've ridden. Stock pipe is strong. I really don't need extra power. Maybe some low end would be nice but that's what the clutch is there for.

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I bought a 03 cr250 built for the woods. I haven't done anything to it but it was close to everything I wanted suspension on a mx bike sucks in the woods. The bike had the suspension revalved and it's amazing. I also have a rekluse but that isn't a must. Also larger tank, rotor and pegs. There is one thing I want to do is a pwk air striker carb. I really like my bikes jetted well and the tmx mikuni sucks. So if I were to build a cr250 for the woods, suspension and carb would be #1. I also have a turbine core for a silencer. Spark arrestor is a must for most areas I've ridden. Stock pipe is strong. I really don't need extra power. Maybe some low end would be nice but that's what the clutch is there for.

Sweet bike. I agree with you on the mikuni carb it does suck to get the jetting on point. With bit of temperature difference and the bike needs to be rejetted. I will be buying the pwk air striker. I called jd jetting and they said they had a fix for the carb. The fix is throw the carb as far as you can into the woods and leave it there and buy the air striker.

I have an 06 cr250r

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I just swapped a Yamaha Warrior for a 2003 CR250. My riding preference is enduro/trail riding (more technical over fast), and not MX. Without any major engine work or breaking the bank, what is the best bang for the buck to make this bike suit my riding style (flywheel weight, gearing, etc.)? What tuning of the engine itself can be done? It has a full FMF exhaust, but is otherwise stock.

If it was mine I would sell it and buy a kdx if I was only riding woods.

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If you are looking for more low end torque from the motor, the best mod you can do is have the cylinder lowered by .030" and the head cut for whatever gasoline you want to use.  Eric Gorr will do this service for $99 and it is worth every penny.  No other mod, like flywheel weights will do more for woods riding than that one mod.  All a flywheel weight does is add inertia and help the motor to not stall in tight situations, it doesn't add low end.  All a larger sprocket will do is help the motor to accelerate faster, it won't add low end.  Lowering the cylinder adds real low end torque.

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I run a mostly stock 03 cr250 in woods, changes I've been able to make so far are nothing great but having the gearing 13/50, braking and tire setup on point has given me a lot more confidence on the trails. I can't say enough about the tubliss tire system, running a 4-5 psi rear and 7-8 front is night and day vs tubes.

I'm going to follow this because I'm now at the engine and suspension changes and can contribute what if find.

Flywheel weight yes if your really using the low end grunt cause I know I stall mine here and there when my clutch hand dies.

Then again like frdbtr says above the cylinder base mod is the number 1 best bang for your buck as far as gaining low end and I'm just waiting for my next rebuild to dive into that one.

Edited by WeekendRDR

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Nothing against a Gnarly pipe but for the price porting is a much better mod.  You can get a full porting package from Eric Gorr for $225 (low/mid, "mo betta" or Mid/top).  A pipe will cost you roughly the same thing and the porting will give you a much better bang for the buck. IMO, pipes, reeds and what not are gimmicks that move the power band slightly in one direction or another and cost an arm and a let to do it.  Porting is a much better option.

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Nothing against a Gnarly pipe but for the price porting is a much better mod.  You can get a full porting package from Eric Gorr for $225 (low/mid, "mo betta" or Mid/top).  A pipe will cost you roughly the same thing and the porting will give you a much better bang for the buck. IMO, pipes, reeds and what not are gimmicks that move the power band slightly in one direction or another and cost an arm and a let to do it.  Porting is a much better option.

 

This^

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The bike already has a FMF Gold Series Fatty and FMF silencer. After first getting the bike and riding it a little, I figure the first thing I need to do is give it a good going through. I set all the suspension clickers back to the baseline settings, and adjusted the race sag for my son's weight. This process is what got me figuring I better go over this bike good before we really even bother to worry about anything else, being mainly because everything was so out of whack. Even with my 200-210 lbs on the bike, it only had 72mm of sag. My son is roughly the same weight as the fella we got it from (about 180lbs), and it sagged only 60mm. Clicker adjustments were all over the place. Kinda gave me the overall impression that there's not much telling about everything else. So, this weekend, the carb and reeds are coming out for inspection and cleaning, and I will likely go ahead and pull the cylinder to clean the power valve, measure the bore, and see what else I find. It runs "OK" right now. Might be that once I get it back running like it should, it might just fit the bill without much else. (fingers crossed)

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The bike already has a FMF Gold Series Fatty and FMF silencer. After first getting the bike and riding it a little, I figure the first thing I need to do is give it a good going through. I set all the suspension clickers back to the baseline settings, and adjusted the race sag for my son's weight. This process is what got me figuring I better go over this bike good before we really even bother to worry about anything else, being mainly because everything was so out of whack. Even with my 200-210 lbs on the bike, it only had 72mm of sag. My son is roughly the same weight as the fella we got it from (about 180lbs), and it sagged only 60mm. Clicker adjustments were all over the place. Kinda gave me the overall impression that there's not much telling about everything else. So, this weekend, the carb and reeds are coming out for inspection and cleaning, and I will likely go ahead and pull the cylinder to clean the power valve, measure the bore, and see what else I find. It runs "OK" right now. Might be that once I get it back running like it should, it might just fit the bill without much else. (fingers crossed)

 

I don't know how old or the experience your boy has.  I have an 03 cr250 and my 19 year old son rides it.  I put a 50 tooth rear sprocket on it and the Keihin PWK carb on it.  It came with the fmf fatty pipe and powercore silencer but other than that it is stock.  The bike works well for him because it has a very linear power curve which is good for him.  He only weights about 130 so the bike will carry him well on the technical stuff.  If he gets more experience I will probably get some porting for it.  These case reed CR's have tons of potential.  Anyway, the power curve of the bike might be exactly what your boy's experience likes, even without porting. The 50 tooth rear is a great investment for a stock 03 CR though because they are a bit soft off the bottom.  I bought a vortex steel sprocket from RMATV, I like that one because it is steel but still light. Only $40

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Personally for woods riding on a cr suspension should be on the top of the list of things to do. Mx suspension sucks in the woods. It makes the bike really smooth and helps the rear tire with traction

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Sweet bike. I agree with you on the mikuni carb it does suck to get the jetting on point. With bit of temperature difference and the bike needs to be rejetted. I will be buying the pwk air striker. I called jd jetting and they said they had a fix for the carb. The fix is throw the carb as far as you can into the woods and leave it there and buy the air striker.

I have an 06 cr250r

+1

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Personally for woods riding on a cr suspension should be on the top of the list of things to do. Mx suspension sucks in the woods. It makes the bike really smooth and helps the rear tire with traction

This times 173. The stock engine jetted properly has very good woods power. It is very very easy to ruin an engine with porting, be careful. The stock pipe is also very good.

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I ride 94 cr250 in the trails no flywheel weight pwk carb stock pipe with pro circuit silencer amr coil no Suspension change and I love it I know if I get Suspension work I'll love it 21 yrs old at 115 lbs lol I'm pretty little

Edited by devendontedavid

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Thanks again everyone for your advice. The power curve as it stands is anything but linear. It wants to either putt along, or hit really hard. On the top end, it runs like a scalded dog. It kinda acts like more than just a carb issue along. I downloaded the service manual, and looked at the section on the power valve. I haven't done the test it outlines yet, but will stuck or improperly working power valves cause this. The bike has V-force reeds in it, but stock carb, and a 49T rear. I know that the original owner (I got it from the 3rd owner, but he only had it a matter of weeks. And, as it turns out, I know the 2nd owner, and he didnt do anything to it), at least at one time, raced it in the Black Jack enduro series, because I found a sound test sticker on the head tube for that. I also think at least the front forks have been reworked. It actually handles "OK", but I'm sure it needs fresh oil and seals. So, my next step is to order a top end gasket kit, pull the carb and see what's inside (jet and gunk wise), pull the jug and see if it's been bored so I can see what piston I'll be needing eventually, and clean the power valves. I will take the advice of not worrying about any add-ons, i.e. flywheel weight, etc., at this time. Until I get it running properly as it is, everything else is on the back burner.

Edited by BigShooter

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RE-read post #6 about the cylinder and head cut. Very inexpensive and very effective for this engine. If you do a top end it would be a perfect time to do it. Huge difference in the woods with accurate jetting even with the oem Mikuni. Good luck, that is a great bike.

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my 03 cr250 has the smoothest power delivery of any 2 stroke I have ever ridden.  If yours is all or nothing, you have a problem.  I would definitely pull the powervalve cover and see if it is opening and closing.  It is possible your powervalve is stuck open.

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