New Member with a question

[996pp]

Hi all
I wish I had found this forum years ago. A lot of interesting and fun topics. I've been riding dirt for the past 5 years after I sold my crotch rocket and its been an adventure. I have an 01 CR250 with pro circuit pipe and fmf muffler, other then that its all stock. Last ride I went on my bike would completely bog out and loose power. I've been meaning to get the carb out and clean it, put a new air filter (as its time for that) and put in a new plug and see if that will change anything.
Now my question is how often does the carb need to be re-jetted? Do the parts wear out every so often and need changing? What else should I look into?

 

[dirt bike dave]

Could be you just need a new spark plug. They don't last forever in a 2 stroke, even if they still look good. Once they go bad, even cleaning them is not going to help.

The carb jets don't wear out, but they can get clogged. If the new spark plug and fresh fuel don't fix the problem, there are several things it could be, but I'd try the new spark plug first.

 

[996pp]

Thanks Dave
Hopefully ill get to it next week. I'm an ok DIY'er. How difficult is it to clean the jets. I've done a lot of DIY on my cars and street bike but don't have any experience with carbs.

 

[MXSparx]

How difficult is it to clean the jets.

Simple. Hardest part is removing the carb. Get a manual so you can the location of each jet.
Carb cleaner.
Compressed air.
Should be all you need other than the tools for disassembly.

 

[BrentRichter]

Welcome out here new guy..this forum really is superb for all those who are into dirt bike riding. I am also a newbie out here..so just wishing that you have all your problems sorted out and enjoy your stay here.

 

[TWRT]

If you are going to start taking parts off, how's the top end? When I rode my yz 2s a lot, I would change my top end every year.

Dave

 

[996pp]

Thank you everyone for all the input. I had done my top and bottom end about 2 years ago. It still feels its got good compression.

 

[dirt bike dave]

FWIW, on my old '99 CR250, one of the allen head bolts in the power valve linkage loosened up once, so that the power valve was not opening. The '99 and '01 have the same power valve design.

Bike ran fine at low rpm, but fell flat, and I mean FLAT on its face when you tried to get some power out of it. Like dropping an anchor.

 

[996pp]

Tnx Dave
I will definitely look into the power valve also as I have a lot of gunk around the exhaust outlet rim. Im sure if gunk is there it will also be in the power valve.
Do I need to take the top end off for cleaning?

 

[dirt bike dave]

On your CR, you can check if the power valve is operating quite easily. There is an inspection plug/cover on the left side of the cylinder. I think it takes a 17mm wrench to remove the cover. Underneath that is the end of the shaft that operates the power valve.

Remove the cover and start the bike. Rev it up. If the shaft rotates 90 degrees with rpm, the valve is operating. If the shaft is not rotating, it could be a problem with the linkage (which is on the other side of the cylinder). The parts on the linkage with the little allen head bolts can be tightened by removing the little cover on the right side. I think it has 3 or so 8mm head bolts. This can be done without removing the cylinder.

On my bike I would clean the power valve when I changed rings, so the cylinder was off anyways. FWIW, the '92 - '01 CR250 power valve is a good design and it tends to stay cleaner than most bikes (in my experience).

If you do remove the cylinder for whatever reason, you have to be careful when putting the cylinder back on. There is a 'fork' in the cases that moves the power valve linkage, and a 'pin' at the bottom of the cylinder for the power valve system. The pin has to go into the fork. If it does not, the valve will not work and you will have to pull the cylinder off to align them. It's easy to do right, as long as you make sure the 'fork' is in the correct position when you re-install the cylinder. Since your bike was previously running good, the pin must be lined up properly in the fork. I don't think it can ever jump out if the cylinder was put on correctly.

 

[996pp]

Thanks Dave
If there is gunk inside power valve does that effect operation of the inner parts or just performance? The reason I'm asking is because if I open up the inspection plug and see that its operating correctly should I still take it off and clean it or just leave it until next time I do a top end.

 

[sbest]

Clean fuel and not letting the carb dry out will keep the jets cleanest, so ride often!
The carb does not need to be removed on most MX bikes.
Loosen up the cables or remove their cap, loosen the boot clamps and swing the carb 90 degrees, bowl toward you.
Often you can remove the bottom drainplug to access the mainjet, or remove the whole bowl.

If the gunk around the exhaust (spooge) is liquid, that is good. It lubricates the powervalve.
Good quality synthetic or caster (NOT the same as Castrol) oil will keep the powervalve free forever.

My 2000 KTM 123 is an enduro model and is driven at 50-80% most of the time. 1st ring and piston lasted 7 years.

Steve

 

[996pp]

Thanks for the reply Steve.
I have everything sorted out and have gone on quite a few rides since. The power valve had so much carbon build up it was barely moving. I had bought the bike used and had never touched the power valve in the past 7-8 years I have owned it. It's got amazing power now after the clean, I don't even think it had this much power the day I got it. For the oil part I have been using yamalube for premix since day one and Honda gear oil every 5 rides for the gears.