Help with sons dirt bike

Mellowyellow

Mellowyellow

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Hi guys,

Been a while since I have posted anything on here but I need some help with sons two stroke 2000 cr125. We went out on the trails this weekend with him and his buddies having lots of fun. We mix 32:1 for him but about half way through the ride my son was almost out of gas so instead of running back to town to get more he used his friends gas and found out later he mixes his 50:1. So after that his bike started running strange.
He said it felt like it didnt have the same power and was bogging a bit.

He kept driving it until he could find me on the trails. By the time I got to look at the bike there was a ton of oil coming from the front of the engine. (Looks like exhaust gasket or power value). So I shut it off looked it over and than started it up. Once I started it I put it in gear and it sounded like the clutch was slipping really bad. Couldnt even get the bike to move with me on it.

So we shut it down walked it back to the truck and brought it home. Once home I checked coolent because I thought it may have overheaded badly but coolent was fine. Air filter was fine. So I thought I would run it again for more trouble shooting. fired up fine but the idle went really high and had to shut it down as it just wanted to rev out no matter what I did.

So I am a bit lost, seems to me like bike has good compression.
clutch out of know where starts slipping.
oil and smoke comes out of exhaust gasket area.
idle goes crazy high.

Any suggestions guys as to where to start.
Sorry for the long story but I am sure someone on here will know exactly was wrong.

Thanks guys
 
I don't know much about two strokes and what lettle I do know is a hunderd years old.
If the bike was designed to run on 32-1 and you run it with 50-1 it's kinda like running a four stroke out of oil. It just takes a bit longer to see the damage.
It sounds like you need engine work.
As I said my knowledge is a bit old. Try calling a local dirt bike shop and asking a few questions.
Maybe some one else will give you better advice.
Leo
 
i agree, it does sound bad. but at least considere doing the rings your self?
an engine is an engine, right? you built your 650, so? whats to lose?
 
At 50:1 you dont have enough oil and too much fuel, your fouling the plug. It should look black as night if you pull it out for a look. The problem is also, since your not burning all the fuel properly anymore your loading up the pumping chamber (crank bottom end) with unburned oil. After the volume builds (like you stated the bike ran weird after he filled up) the unburned oil with seep out into the exhaust, powervalve area and then out the stinger end.

The motor should be fine imho. I would do the following, remove the exhaust, kick over the motor a few times (with it off of course) try and empty out the pumping chamber, hang the exhaust from the stinger end to drain the oil of it. Change the plug, check the air filter and carb inlet (for oil coming back out) and change the fuel back to 32:1. Reassemble... should be fine. Might have to smoke it out for awhile (burn off the excess) but without taking it apart its the only way.
 
highspeedhamish, that makes perfect sence to me. I pulled off the exhaust to look up into the engine, slowly kicked it over to see the piston and just from my eye the piston doesnt look to bad (no major scoring or wear).

one more question, would all that oil in the bottom end cause the clutch to slip?
 
I agree.. though engine damage is possible, there is a chance nothing was hurt. The bogging and not running well could very possibly be due to a fouled plug. I have seen quite a few 2 strokes that are pumping out oil from the front exhaust gasket from incorrect mixtures.

As said... drain the gas... fill with proper mixture, while your draining... empty the float bowl. Check the air filter, replace the plug, hell drain the crankcase oil and replace that too.
 
They will be some wear on the piston, the CR series is a high powered engine for sure. I think the piston time to re ring is 20 hours? or less...

The CR is also a unit construction, the clutch and trans are in a separate area of the engine and have their own oil system. If the clutch is slipping it could be worn from him trying to ride the clutch to get the bike move since its bogging down.. its a small clutch basket is those things, I think the 125 makes 26 hp? that's a lot for a high revving engine to put on such a small clutch.
 
Thanks a bunch guys, Im heading out of town tomorrow for the week so I will ding into when I get back and keep you guys posted.

Thanks again for the help guys i really appreciate it.
 
Check your gearbox oil level. If your RH crank seal has gone it will suck excessive oil into your motor from your trans. Low trans oil may have cooked your clutch...?? Running 50:1 will not make the clutch slip, maybe the fibre plates are due for replacment or adjustment...is there freeplay in your clutch cable, your clutch will slip if theres no freeplay.

Good luck.
 
I wouldn't think 50:1 would be that bad. I work at a outboard repair shop and we run 50:1 in all of the two strokes old to new and those engines run 6k rpms. Not sure what your bike runs? The synthetic 2stroke oil has come a long way since the days if running 20:1.... IMO
 
50:1 isnt bad if you jet for it and have a reason to jet for it. With Optimol you can go 100:1 without worry. The CR125 redlines around 11,500 rpm so its moving a lot of air and gas in order to make 42hp. (I thought they only made 27..wow).

If you didnt change the jet when running 32:1 and then you switched to 50:1.. your putting more gas, less oil into the main jets passage way. So your running rich by thinning out the oil mix. Unburnt gas and poor combustion wont burn away the oil and hence the build up. Im sure your boat engines have a much larger displacement than the CRs 125cc cylinder hence run 50:1 without problems.
 
Ok Guys so I got home the other day and drained and cleaned the exhuast reinstalled with new gasket and rtv sealent, drained the tranny oil, flushed and refilled. Inspected air filter cleaned and reinstalled, drained fuel including carb bowl and refilled with proper mixture. Bike fired up fine smoked like a basterd so I kept it running in hopes it would clean it self out. After 10 minutes it still smoked (grey) like a basterd and oil was comming out of the exhaust. The oil smelt like fresh unburt oil (kind of like the fresh oil I just put in the tranny) I also sprayed ether all around the bottom end of the engine with it runnung (looking for rpm change) to try and see if it was a crank seal and didnt notice any change. Also the clutch is still slipping like a basterd and barely moves the bike when in gear with no rider on it.

So here I am again lost any suggestions????? Please Help
 
Do a compression check. I think the ring is smoked. There's a chance you blew a head or base gasket and its sucking in air, that would make your idle rise. The oil may be actually coolent blowing by. When my son raced 50s we always ran 50:1. He is on 85s now and I run 40:1. Remember a leaner mix does make it run rich. I don't think the gas caused it,its just time for a rebuid. We ring them at 20 hours and replace piston every other time. Compression test and leak down will tell you a lot.
 
I think Hotdog has it nailed. What has happened is likely unrelated to the change in premix ratio. 50:1 is a little lean on oil to me, but I'm an old timer; modern two strokes run a lot less oil than we used to think they needed. But the problem is that you have TOO MUCH oil going through the engine. There is only one place for this to come from - the tranny; more specifically the clutch side seal to the crankcase. This would cause the engine to bog trying to burn too much oil, plus now the clutch doesn't have enough oil any more. The tranny is likely undamaged, but you may h ave smoked the clutch plates. Repair may or may not be a big deal. If the seal can be replaced with just the removal of the clutch (from the outside of the center cases), this is not hard at all. However, some manufacturers install this seal from the inside, which means splitting the cases. I have done this, but it usually involves a lot of brute force and washers, shims, bearings and spacers all over your bench, then where did that shim go? etc. As I say, if you've got excessive smoke with the proper mix in the gas, there is only one source for the oil... Hope this helps.
 
Thanks Guys I have been kinda thinking that the mixture may have been just a coincidence.

And yes this all makes sense it sucks but makes sense. I still dont have my 650 on the road between fixing other bikes and the honey do list I should be done in about 5 years lol.

Thanks guys
 
Might wanna pull the clutch out too and inspect. It sounds like it's toast. Gotta love dirtbikes. lol
 

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