My YZ is being lazy. %#$&

[Blisterphish]

I purchased a well-used 96 YZ 250 at the beginning of the summer. It has always sputtered a lot at higher RPM just after starting then idles poorly after warming up. It kills very easily and kick starting is a #$&!

Last week I went for a quick ride and got about 500 yards before the bike began to make a very throaty sound and died. The sound was the same as if you had the choke on and hit the throttle…..kind of a hollow sound.

I grabbed the Clymer book(after pushing it back home) and began troubleshooting. Here is what I’ve done so far.

New Plug
New Plug cap
Tested Coil resistances – Good
Checked all electrical connections – Good
Checked Stator Coil resistances – Good
Pulled the carburetor and completely disassembled and cleaned it.
Set Jet Needle to the #3 position, which is stock. Someone had it set as lean as possible #5. I don’t know why. The jets are stamped with the stock numbers and did not appear to be clogged.

Flywheel was rusty and filthy and the stator coils were very dirty so I cleaned them all before reassembly. I figured that was the problem but no dice. I can smell fuel and the spark plug is wet after I try to start so I know it is getting fuel. I had just cleaned the air filter and the box looks pretty good so it is getting air.

I am to the point where I think it must be the CDI unit, which costs about $120 or something completely different. I’m hoping some of you have seen this before and can put me on the right trail before I start throwing hundred dollar bills a this thing. I'm at a loss... :bang:

Thanks in advance,
Dave.

 

[wornknobby]

well i didn't see it mentiononed above, so i will ask, did you ground the plug to see if your getting a good spark?

my old kx did the same thing and even looked as though it had good spark, but until i bought brand new coils i then knew how much better it could have been.

 

[Blisterphish]

I did ground the plug and saw and heard spark. Weather the spark is good enough for quality combustion I don't know. I do know that the spark seemed stronger after putting on a new plug cap.

 

[Blisterphish]

the book mentioned that the spark should be fat and blue. It is not. It seems strong but it is white. ???????

 

[robwbright]

What's the plug look like when you pull it?

Have you tried a Wide Open Throttle plug chop?

Are the reeds in good shape?

Has the silencer been repacked?

Are you sure it's not a jetting issue?

Just because you went back to stock doesn't mean it's right. Dad's bike did a similar thing until he got the jetting straightened out.

http://www.ericgorr.com/twostktech/carbtuning.html

 

[Blisterphish]

1. The plug is coated with fuel but clean.
2. I don't know what a throttle plug chop is. sorry
3. I've not checked the reeds.
4. The silencer has not been repacked since I've owned the bike and maybe never for that matter. I suppose no air out is as bad as no air in huh?
5. I don't know enough to know if it's a jeting issue or not. I do know that the guy I bought the bike from knew less than I do but thought he knew a lot so him tinkering would not be a surprise.

The packing of the silencer should be done how often? Can it get so clogged that it keeps the bike from running correctly and then finally not running at all?

I'm a newbie so any info you care to share if valuable.

Thanks,
Dave.

 

[sick 96 250]

sounds like a jetting issue or carb floats are out of whack. You said the jetting in there was the stock jetting? Stock jetting is pretty rich and almost always need to be leaned out some on 2 stroke bikes. When was the last time you did a top end? With the rich jetting and possibly your top end being warn this could be making it hard to start. Also make sure your floats are set to spec, could be letting to much fuel come through on start up as well and wet fouling the plug so it wont start. Also have you checked your reeds for cracks or chips and make sure they sit flat on the cage. And last thing you said your flywheel was rusty and really dirty, this could also be where the problem is coming from, something in the mix of that, as far as i know dirt/debris and water should not be able to get to your flywheel so maybe it messed something up being so caked with crap. For parts just watch e bay, normally you can get CDI's, stators, etc pretty cheap

 

[John Cena]

How old is the piston?

 

[Blisterphish]

Thank you for your responses:

I just got the bike this summer and have not done a top end. The guy I bought it from did not do it either but I'm not sure how much he rode it. I could be the 10th owner for all I know though.

I will check the reeds tomorrow to see how they are looking. The floats look brand new and I made sure they were to spec when I put the carb back together; it almost looked like the carb had been rebuilt not to long ago. The flywheel cover is obviously letting junk past the gasket so that will have to be replaced. I've been expecting to have to do a top end but I was hoping to get through the season and do it this winter. May have to do it sooner. I'll also have to look at repacking the silencer and I'm still curious to know what a throttle chop is.
Thanks again,
Dave.

 

[weez440]

sounds like a tired motor i would just give her a top end and then away you go. either that or before you would do anything give it a compression test i dunno what they should run 130? i guess i dunno on dirtbikes i am sure one of these guys could tell you what the compression should be. and i got a brand new YZ if you wanted to i got a compression tester i could take the compression off of that and let you know what mine is running.

 

[Xtremesports445]

the plug throttle chop has to do with testing whether or not your main jet is lean or rich or just right. http://justkdx.dirtrider.net/carbtuning.html you can find that test and others at that site. it's under the "Tuning from idle to wide open throttle, plug reading" section.

 

[tyler hougen]

hey ne one know about fork oil specs?

 

[Blisterphish]

Thanks. I have the book and it should have the compression specs. My toolbox is getting full with the odds and ends that I have to buy to keep this thing running. I love it though.
I have to admit I love it more when I'm riding it then when it's sitting in pieces in the garage. DOH!!