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help me trouble shoot my new/old dirtbike...

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i took a 94 RM250 2 stroke in trade a couple weeks back. ive been on it about 6 times in the last couple weeks, and rode the devils racetrack in the san rafael swell last weekend. i struggled on the steep rocky stuff. it seemed that i had to take it twice as fast as everyone else, or my bike would stall. that made it tough to pick the right lines.

im new to dirtbikes, with no previous experience. my buddy came over last night and wanted to ride my dirt bike. he took it up in the mountains by my house, and came back about 30 min later. he has owned a few different dirt bikes, and says something is wrong w/ mine for sure.

he says its way underpowered for a 2 stroke 250, and it isnt running right. he says he cant believe i took in on trails running as weak as it is.

there is almost NO power in 1st gear until the powerband. you cant even get the front wheel off the ground even with significant effort and lots of clutch.

any ideas on what to check first? my friend says he thinks it sounds like it may need a new topend/piston. any input would be appreciated.

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assuming you haven't checked ANYTHING, i would start wth the airfilter. also change the spark plug wouldnt hurt. if that fails, either you're gonna need to replace top end, or change/adjust your jetting. to do that you should start by setting your float height in your carb, theres a lot of good threads in here about jetting if you search for them. also good gas could help too, you should at least be running 93 octane.

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Sounds like jetting to me. Clean and oil your air filter. Take your carburator apart, including your jets, especially the little pilot jet that most people neglect. soak, and clean everything good. Make sure all passages in the pilot jet are good and clean (this is most likly your problem) by carefully poking a small piece of wire through all passages, especially the ones on the side of the jet. rinse all the parts, and blow them dry with a shot of compressed air. Put it all back together according to spec. Before you put the float in, put it by your ear , and shake it. You are listening for any fluid in it. If your hear fluid, the float is no good. check the inlet needle, and seat for any wear. A magnifying glass is really helpfull. The bike SHOULD work much better now! If it does not, rebuild the top end. For the price of a new top end, it should be done anyways, just for piece of mind.

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The bikes 13 years old. When was the top end done last? If it were mine, first thing I'ld do is pull the head and take a look.

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Check the air filter, the exhaust for splooge (rich), the plug for fouling and then check the cylinder for compression. Also check the reeds which isn't the easiest thing to do, but if you don't know the history of the bike, they could very well be worn/cracked.

I would NOT take the carb about right away or at least not until you check the reeds. I'd check the other stuff and then throw into the fuel tank about 10-15ml of methanol or acetone which raise octane and clean the carb. (Methanol, ethanol, and acetone are higher octance, but less energy dense which is why ethanol/methanol only engines use much larger jets and hence you much larger amounts of fuel over the same distance........therefore, if you are using those additives while keeping the jet size the same, you are leaning out the engine. If that addition makes it run better, you know it was running rich. You can also use this knowledge for sea level to high altitude riding so you don't have to change your jets, but that's another subject.)

If it's a dog on the bottom end and then takes off high, it's more likely running rich and/or the plug is fouled.

If it were a dog at all levels I'd be more inclined to say it's compression.

Nevetheless, if you don't know when the top end was done it's likely you're in for a new one and don't forget to check the reeds!

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ok...tonight i pulled and cleaned the carb. it was a mess. tomorrow ill try to find and check the reeds, air filter and exhaust. how do i get to the reeds?

also, i live at 6,100 ft above sea level in utah. here is a pic of the carb mess...

carbft9.jpg

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the reeds are right in front of the carb or where the carb goes into the engine just pull em out and check to see if any r cracked or bent

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The reeds are inside the tube going into the engine which the carb was attached to. Since you already have the carb off you can get to the reeds by removing the 5-6 bolts holding the manifold/tube to the engine case.

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I dont see the pilot jet in your carb picture. You absolutly must pull that out and clean it thoroughly by poking a small peice of wire through ALL the passages in it. By the way you described your bike as being a dog untill it hit the powerband, and the mess you describe the carb being, your pilot is plugged. Without cleaning it your bike will run no better, and you are wasting your time!

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thanks for all of the help so far.

ok, i pulled the reeds and they look like they are in good shape...nothing unusual.

i also pulled the muffler, and would like to repack it. the bolts seem to be really tight. any suggestions?

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I dont see the pilot jet in your carb picture. You absolutly must pull that out and clean it thoroughly by poking a small peice of wire through ALL the passages in it. By the way you described your bike as being a dog untill it hit the powerband, and the mess you describe the carb being, your pilot is plugged. Without cleaning it your bike will run no better, and you are wasting your time!

thanks for checking me...im not sure which is the pilot jet. what should it look like? i dont want to put it all back together without cleaning all the right parts.

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Turn the carb body upside down. The pilot jet requires a small slot screwdriver, one of those pocket ones work great. The jet is fairly deep in the body, and you can only see the slotted head, look for it. Do a google search for your brand of carb. All kinds of info. sites will show up. or use a manual.

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Turn the carb body upside down. The pilot jet requires a small slot screwdriver, one of those pocket ones work great. The jet is fairly deep in the body, and you can only see the slotted head, look for it. Do a google search for your brand of carb. All kinds of info. sites will show up. or use a manual.

got it...its good and clean. didnt appear to be clogged. thx.

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Didn't appear? Did you check the 4 tiny, hard to see passages on the side of the jet? I always clean them with a small piece of wire from a wire brush, even if they "appear" clean. Any varnish in those passages will restrict flow.

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Didn't appear? Did you check the 4 tiny, hard to see passages on the side of the jet? I always clean them with a small piece of wire from a wire brush, even if they "appear" clean. Any varnish in those passages will restrict flow.

sure did. the 4 holes were clean and free of any obstructions.

next is getting the ends off my muffler for repacking. then, a friend is comming over tomorrow to help me take the top end down and look at the piston & cylinder.

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Make sure your reeds sit flat and are not curled on the ends.Take a flashlight and look them over good look for any crackes if you see any replace with new ones.Good luck hope you get it going.

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ok guys...we are making progress. here are some updates. i pulled the reeds and they look great. no cracks or bends. removed the exhaust pipe and radiator, and my buddy came over. he suggested we do a compression test prior to pulling the piston. the kick measured 125 - 130 PSI. he then suggested that we take a look at the power valve. we opened it up, and found that the little vertical rod had a worn plastic connector on the end of it. it wasnt even attached to actuate the power valve. im thinking this may have been my entire problem.

so...a couple questions:

-is 125 - 130 PSI a decent compression reading? if so, i may not swap the piston until next winter.

-where can i order the small plastic connector that is worn in the power valve box?

-on the other side of the power valve box, how do i know how it should be adjusted for woods riding?

-i got the 6 bolts off of the muffler. how the hell do i get the ends off? they dont even budge.

any other suggestions would be appreciated. thanks for all the input thus far.

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ok guys...we are making progress. here are some updates. i pulled the reeds and they look great. no cracks or bends. removed the exhaust pipe and radiator, and my buddy came over. he suggested we do a compression test prior to pulling the piston. the kick measured 125 - 130 PSI. he then suggested that we take a look at the power valve. we opened it up, and found that the little vertical rod had a worn plastic connector on the end of it. it wasnt even attached to actuate the power valve. im thinking this may have been my entire problem.

so...a couple questions:

-is 125 - 130 PSI a decent compression reading? if so, i may not swap the piston until next winter.

-where can i order the small plastic connector that is worn in the power valve box?

-on the other side of the power valve box, how do i know how it should be adjusted for woods riding?

-i got the 6 bolts off of the muffler. how the hell do i get the ends off? they dont even budge.

any other suggestions would be appreciated. thanks for all the input thus far.

also, the compression test was done while the bike/piston was cold. any ideas what a normal reading would be? im trying to determine whether or not to order a piston kit. thx.

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Rebuild the top end while it's apart. You've got half the work done anyway, a Wiseco kit is around $130 and it's a hell of a lot cheaper to do before you seize it. Do it and :applause: with peace of mind.

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I agree! For the cost of a new topend, do it! Your psi is OK, but barely. According to the owners manual for your bike, you are to replace the piston after 25 hrs. of use. How many hours does yours have on it? I thought so. Change it! Are you going to take a chance and save yourself 125 bucks? Wait untill a piston skirt breaks off on a high speed straight, jams itself in your crank, destroying it, the rod and your cyl!!! And then dumps you on your head when the motor locks up. Then you wake up shaking your head saying Then you discover your motor is fragged, and you say :applause:!!!!!!!:applause:!!!!!!:lol: !!!!!! Then you ask yourself:excuseme: But deep down inside your doing this:banghead: All because you didnt listen to our advice:bonk:

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