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03 cr250 question

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My first post. Hold your applause please.... I'm new to 2 strokes. I recently bought an 03 cr250. It was professionally rebuilt. New top and bottom. V force3 reeds. DEP pipe and silencer. It has about 15 hours on the rebuild. It has the stock mikuni carb with a 390 mj, 30pj, and not sure what the needle is but the clip is at the top groove or leanest position. Air screw 1.5 turns out. Stock is 420mj, 30pj, needle clip 3rd groove, air screw 1.5.  The guy I bought it from was using half race gas and half pump and a premix ratio of 80:1. I can't remember the brand of premix oil and calling him is not an option. I think it was motul 800 or maxima superM???

 

Here's the problem. I ran the bike around the yard slow to medium speeds with the gas and premix he had in it. It pulled good bottom and mid. No top end really, just made a lot of noise. But im a bottom to mid rider anyway. It smoked a little on startup but clean after it got warm. No splooge. When i got through running his gas out I decide to take the carb off, clean it, see what jets it had etc. All good , put the carb back on. Checked the power valve operation( I tightened the cables just a hair). All good. Went to the store and bought Lucas 2 stroke oil and Straight 93 non ethanol gas and mixed it at 40:1. ( 80:1 scared me).  Put it in the bike and it fired right up. The barely bottom runs ok but give it any throttle at all and it smokes like a freight train and doesn't pull hard, just makes a lot of noise. Still no splooge though. My carb is already setup pretty lean and by adding more oil to my premix it should be even leaner from what i read. If its lean then why is it smoking that bad. Will a lean running 2 stroke smoke. And dangit wheres all the power?

  Thanks for the help

 

 

I posted this in the tech forum before i saw the Honda specific page.

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Update: i put a new plug in and rode a little more. Still the same.  Just for kicks I pulled the choke up and rode and that didnt change anything either.

 

Any ideas?

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Thanks, I will. The only thing is, it was running fine before I put new gas in it. I also just read on another forum that the o-ring seal for the pipe can screw things up if not creating a good seal. My oring is flat and wore out and definitely not sealing 100%. I had pulled the pipe off to look in at the powervalve flaps before the bad running started.

could this be my problem? I did also notice it leaking a little before i pulled it off.

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What do you know about the motor? Has it had any machine work done to it? If so that is why the previous owner was mixing race fuel, just running pump gas would have detonation issues. I would stay with at least 40-1, service manual suggests 32-1. I doubt your o ring is the problem but I would definitely fix. Sounds like your going to have to start fresh with Jetting, what's your elevation etc. I would first still do a compression test to find out if it has high compression and your going to need better fuel. If you can post pics of your plug that may help also.

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The other thread was talking about melting the rings near the exhaust port. Generally that results in catastrophic failure and seizure so I don't think that's the right road to be going down for this.

However, if you take off the exhaust you can see right in and have a look at the piston rings for yourself.

I would first try draining the gas tank and putting in what the other guy was using and see if that fixes it. If it does fix it and you still don't want to use that gas, then reset your carb to the new mixture.

If it still won't run right with the original blend then go from there.

Edited by runnybunny

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Check the exhaust flange. If it makes a lot of noise and has no power, you could have screwed that up and it doesn´t seal properly. It does have attachment hooks for two exhaust springs. One goes on top, the other one to the right hand side (seen from sitting on the bike). So when you sit in front of the bike looking at the exhaust flange, it´s one at 12 and one at 7 o clock. If you put it at 12 and 5 o clock, the flange will not seal because the spring is blocking the space between the flange and the cylinder.

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I would play with the jetting. You're much leaner than he had it.

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Thanks for the help so far. I agree that with the new premix ratio it should have leaned it but would it smoke that much if it was lean. Also my carb settings are already very lean. 390 main vs 420 stock and needle in the top clip position. Also i did a quarter to half throttle plug chop last night and the plug came out on the tip slightly glossy black???? Maybe i messed up the float when i pulled the carb off. I will pull it and check it a little later.

I also picked up a compression tester this morning and a new oring for the exhaust flange. I will do some testing and let yall know what i find.

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Alright I did a compression test using the $30 tester from oreillys. I got a consistent 165 psi. What kind of numbers do some of yall get?

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10-4 the thread adapter was the same length as the spark plug. Is 165 super low? I read where people get 2 different numbers from 2 different gauges. Also it was running fine( as far as i know) before running out the previous owners fuel mix out and putting my own in. I also cleaned the carb during that time. Would a float set too high cause the symptoms i am having. It seems to run pretty good at idle and barely past. But more than that and it gets bad.

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I know when it's time for a fresh topend rebuild by the kicker & how the comp. feels thru the stroke.  165psi is on the low side & would indicate a need for a fresh topend.  You want to be close to the 190-200 psi range with a fresh piston depending on if it's had mods for more comp..  If you recently picked up the bike chances are it needs a fresh topend.     Did you hold the kill button down & hold the throttle WO till the psi. stopped rising on the gauge ?

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165 is lower, but not horrible....and I don't see the float causing your issues either.

Like these guys said, sounds like you need to work on the jetting or try to find race gas in your area and go back to what the PO was running.

When I bought my 03 I rode 2 others and both had jetting issues with the stock carb, even the one I bought.  I put my Lectron on it and it runs perfect.  I didn't do much research on the stock carb but based on the 3 bikes I rode I would say the stock carb has some issues and is sensitive to changes.

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H4L, I did hold the kill button down and the throttle wide open.

 

I pulled the carb again and checked the float. It wasn't far off. Then I pulled the float assembly out and checked the rubber needle and seat. The rubber needle has a bad uneven groove in it. Maybe fuel is leaking by? Reckon that would cause the richness? I just cant understand why it was all of a sudden. If it is the problem then i suppose I have to decide whether to buy needles, seats, jets, nozzle maybe, or just get a keihin.

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H4L, I did hold the kill button down and the throttle wide open.

 

I pulled the carb again and checked the float. It wasn't far off. Then I pulled the float assembly out and checked the rubber needle and seat. The rubber needle has a bad uneven groove in it. Maybe fuel is leaking by? Reckon that would cause the richness? I just cant understand why it was all of a sudden. If it is the problem then i suppose I have to decide whether to buy needles, seats, jets, nozzle maybe, or just get a keihin.

I'd recommend replacing the topend & checking the bottom end while top is off since it's a used bike you just picked up.  It can potentially cost you more down the road if the piston goes & takes the Bottom / top of the motor.  Do you know how many hr's are on the piston ?

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I'd recommend replacing the topend & checking the bottom end while top is off since it's a used bike you just picked up.  It can potentially cost you more down the road if the piston goes & takes the Bottom / top of the motor.  Do you know how many hr's are on the piston ?

 

I agree. Trying to jet a worn out engine is a waste of time. Then replace the carb if you want. 

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So before you go rebuilding the thing try a different compression gauge. Those things are not very accurate. I have 4 of them from different manufacturers and they all read differently. Some will read high some low. The important thing is to know how yours typically measures then base judgement from that.

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Ya i feel like my compression is good even tho the gauge said 165. It feels like it has good compression when i kick ot over and it starts very easy like second kick every time. I did thin my mixture down today to 80:1 like the PO had it and it did take care of some of the smoke but it still ran like crap. Wierd thing is the plug came out looking perfect. I am getting a gallon of av gas tomorrow to see if it helps. The PO said he was running race gas and pump 50 50. Not sure the difference in race gas and av gas but im gonna try it.

As far as i know my engine is stock with a top end and hot rods bottom end that is only about 15 hrs old. I have receipts where it was done. No porting as far as i know.

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Alright its been a few hours later and i rode the bike again with the 80:1 mix. The smoke finally cleared up and my power came back tho you can tell that the jetting is not spot on.

That being said, i dont want to run the bike at 80:1. My preference is 40:1 but that smokes like crazy. I guess that can be cured with proper jetting???? But going from 80 to 40 I should technically go fatter right??

It just doesnt make sense to me to throw more fuel at it when its already smoking. Or does it? Anyone else have the same experience?

Thanks for the help so far. It's a fun but frustrating learning curve on these 2 strokes

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