WOT too rich, lean, or somthing else?? Please give opinion 00 YZ250

NateZ

Member
Feb 27, 2005
83
0
1. Riding with a 95 cr250 today we opened it up on a long straight (i have a 2000 yz250) And we accelertated at the same pace, until about 1/4 way through 5th gear, then he started pulling on me hard! WTF? Im 30 lbs lighter than him, plus my bike is lighter by a few. Both have the same gearing. Whats goin on here you think? The bike doesn't feel like it is opening way up when i give it more than 80% throttle or WOT. (it seems to change to a lower pitch when given WOT) Before i start doin a plug chop and mabye clean the carb/see what jets are in etc, what do these symptoms sound like so i have an idea of what im lookin for? Too lean or too rich up top? Could a silencer than needs to be repacked do this?

2. Also, when cruising at part throttle keeping a constant speed, the bike surges, not s smooth cruise. What do i need to adjust for this?

Thanks,
Nate
 

joe265

Member
Feb 13, 2005
42
0
. Was the bike running good until now? Or is this something that just surfaced? Sounds like it's running lean. Put a fresh plug in it and run it through the gears wide open a few or more times and check the plug. If it's still white then you could have a clogged carb or possible reed problem. I'am also taking in consideration the jetting is right and the bike just started doing this recently. Good Luck...... :)
 

reelrazor

Member
Jun 22, 2004
340
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A) clean that silencer first thing if you suspect that. It doesn't do any good to start playing with jetting with other things like that affecting it.

B) I agree with Joe in that you sound lean. By lower pitch, do you mean the exhaust note sounds kinda flat? Lean.

You may find that you need a little higher needle and maybe more main jet.

Was it cooler than average that day?
 

NateZ

Member
Feb 27, 2005
83
0
I just got the bike, so it's been doing it ever since i started riding it. Yes the exhaust note flattens out. The bike is completely stock. I will clean out the silencer, and check the plug. Nope it was about normal temp. About 89 degrees. I'll put a new plug in it now and do a plug chop and see what color it is.

Nate
 

NateZ

Member
Feb 27, 2005
83
0
Ok just did a plug check with new plug , it's def lean. Plug was white. So up one or two on the main jet? Also you mentioned a reed problem? Would they be cracked or?

Thanks,
Nate
 

Micahdawg

Member
Feb 2, 2001
503
0
Check the carb vent tubes that they are not clogged. I just bought an 01 RM 250 that was in very good shape, but the plug was lean and the idle chopped around a bit. One of the vent tubes was plugged with dirt and the other crimped shut. I haven't put everything back together yet, but on Eric Gorr's site he claims that clogged vent tubes can create a lean condition.

You should probably change jetting last because if you've got some other problem then changing jets may not help.

Micah
 

NateZ

Member
Feb 27, 2005
83
0
Ok guys heres what i have done:

1. Pulled the petcock to clean it, there was alittle crap on it, but nothing that would clog it. Cleaned.
2. Checked all the lines, they are good and clear.
3. Took the carb out and cleaned out all the passages and jets.
4. All the jets were at the stock settings. (size wise) The jet needle clip was at one notch lean, so i put it back to the stock position of number 3.
5. Reeds looked good, no crap in them, no cracks or anything like that. HOWEVER i don't know if they are stock or not, do they require special jetting for aftermarket ones? AND if so, do aftermarket reeds make the bike richer or leaner?

Otherthan that, everything else is good. My mix ratio is 32-1 btw. So i guess the only thing i could do is try a 178 main jet to richen the top end up (stock is 175), is it unusual to richen up a main jet on a stock bike, especially when considering the temps down here are around 80-90 degrees? If there are upgraded reeds in the bike, and it was not jetted for them, could this be the problem?

What do you guys think? Please help me out.

Thanks,
Nate
 

NateZ

Member
Feb 27, 2005
83
0
Aftermarket reed jetting

Do aftermarket reeds generally make a bike richer or leaner on the top end? What about on the bottom end?

Thanks,
Nate
 

WillyM

Member
May 18, 2004
84
0
It is normal to re-jet a stock bike if you want it to run at optimum.
Remember that the jetting is effected by ambient temp ,humidity,and elevation.
To answer your other question the reeds shouldn't effect the jetting that much.
It sounds like you could have a crank seal going also the way to tell is a leak down test, this is a guess though without hearing it.
 

NateZ

Member
Feb 27, 2005
83
0
Crank seal?!!?! Oh man that would definatly suck. Can a dealer do the leak down test? Should i have it done before i run it anymore?!

Nate
 

Kawi4life

Member
Feb 21, 2005
105
0
Woah.. hold on.. don't get all worked up just yet. Your bike might be just fine.

NateZ said:
is it unusual to richen up a main jet on a stock bike, especially when considering the temps down here are around 80-90 degrees?

I would say in some rare cases some stock bikes require richening up the main jet. For example, when my friend bought his brand new 1991 YZ125, it was so lean on the top-end it would cut out bad when wound out and forget about white spark plug colors, the inside of the silencer was even GLOWING cherry red!

I forget how many steps up he had to go on the main, but once he richened it up, it ran fine every day since. I bought the bike off him and owned it for a year or two and had no problems with it. So I say try changing the jets. It's cheap and very easy to do.
 

High Lord Gomer

Poked with Sticks
Sep 26, 1999
11,790
34

NateZ

Member
Feb 27, 2005
83
0
Could it be possible that a chain that needs to be replaced would cause me to loose so much power up top?

Could it also be possible that my ignition is causing me to loose the power and it needs to be adjusted?

Nate
 

NateZ

Member
Feb 27, 2005
83
0
Yea it was clear and not messed up. If the plug wasn't as white as i thought it was (im having second thoughts, mabye the plug isn't as white as a lean plug should be, as in no white specs on it) what else could my prob be? I mean my 95 CR only has boysen reeds, and a procircuit silencer, thats it. How could it beat my 00 YZ like that?

Nate
 
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kxmike

Member
Feb 2, 2005
65
0
how about a 2003 kawasaki kx125 with vforce delta 2 reeds? im at stock jetting. is there a chart for the vforce or is it the same as the boyessen
 

gonzo843

Member
May 24, 2004
199
0
Expect to jet leaner still. For example, my 125 comes stock with a 40 stock. I am now down to a 35 with Boyesen reeds and a Factory Fatty pipe and shorty silencer and it's 40 degrees outside.
 

Kyleb15

Member
Oct 8, 2004
116
0
Hey guys, I had a problem similar to yours were the top end was really flat and not much power. Turns out my powervalve pushrod was snaopped and the powervalves were stuck closed you might want to check those valves.
 

joe265

Member
Feb 13, 2005
42
0
If it is your ignition side crank seal, you could take off the ignition cover and when it's running spray some carb cleaner liberaly at the seal and see if you notice any change in the engine speed, it shouldn't have any effect on the engine if it's sealed up still. If you don't find anything there then go back to basics, you will almost always find your answere there. Check compression, jetting for your altitude and avg. temp/humidity, ignition timing, plug heat range/gap. Make sure your powervalve system is functioning properly. Hope my .02 helps....Good Luck!
 
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