YZ250 pings bad and is running rich

Bike has fresh top end with about 2 hours on it. Has FMF fatty and FMF shorty exhaust on it. I run 40:1 with 91 octane fuel.

 

I've searched and read the FAQ section but I'm having trouble here. Let me start off, I'm a new rider and i'm still scared to move the much throttle except for short blips. My bike has no problem going in slow technical areas. The problem is when I'm at about 1/4 throttle or more the bike starts pinging bad in the upper rpms. I've read enough to say this is from being too lean. Well I took the plug out and it's solid wet black, the slincer has oil driping on it as well as some spray on the white number plate next to it.

 

Splodge aside I took the carb apart. The jetting is as fallows main jet is 178, pilot jet is 50, neddle is on 3rd ring and air screw is 1.5 out.

 

I took apart the silncer and the fiberglass weighed about 100lbs in 2 stroke oil lol. I probably couldve rang it out and recycled it! So I'm going to repack it today.

 

So does anybody have any seguestions? I'm going to repack the silencer, clean the expansion pipe (internally, some how...) and check my carb float level. Any other ideas besides race fuel?

 

Thanks,

Brett

Clean out the carb. Make sure everything in there is clean and not obstructed. What elevation are you running the bike at? I'm close to sea level and have a 45 pilot, 172 or 173 main ( I forget) and the clip in the middle. The next thing to check is the ignition timing.

 

Could be rich on the bottom and lean up top. I'd look online at pictures of plugs. Sometimes they can be deceiving. Rich outter wet and black and light and lean on the porcelin.

I cleaned out the carb last night. It looked really clean. Checking the timing is going to be a little tough because I really don't want to buy a tool i'll just use a few times. Maybe I can find a tool that would work at harbor freight lol.

 

I live in Tucson, AZ so my altitude is at 2500ish feet. A lot of the local trails are around 4000. You're right about the being to rich on the bottom end (I spend a lot of time there).

OK I just checked the float level. It's at 7mm so that's good to go. Couple more things to check before I get out the gas can and match.

Edited by 2011GT

You can make a tool to check the timing for like $12. There is a DIY thread on this forum, I found it via google searching for "how to set timing on yz250"

 

It sounds like you have a jetting issue and the timing is advanced too much. It would be either of those two or the bike overheating causing it to ping.

 

Also, are you certain it is pinging and not a vibration? The two can be very similar if you don't have a very good ear for detonation...

Also, remember that if you pull the plug out at home after you are don riding, you are only seeing what the last couple seconds of operation looked like (likely idling back to the truck), so it really wont give you any information about what is happening when you are hearing the pinging sound.

 

You want to hit the kill switch immediately as you hear the ping, and pull the plug. That is the only way to see what is happening at the time of the event.

YZ's are spoogy by nature.  If anything, you're too rich - I wonder if its stumbling at higher RPM's, not clearing out?  I'd try a 175 and drop the needle clip one spot. 

 

To really dial out the spooge, you gotta look at squish and such.  Thats phase 2. 

OK, I went to harbor freight and picked up a dial gauge. My timing was advanced about 3/4 of a degree. I backed it up to 1 degree retarded or a total of 1.75 degrees. No more detonation!!! WooHoo. Except I think I lost about 30% of my power haha. Right now the power level is fine for me being a beginner and all.

 

Will the top end last longer with the timing retarded?

Is your bike a pre 2007 yz250? If so, a N3EW needle will help in the low throttle range you describe.

OK, I went to harbor freight and picked up a dial gauge. My timing was advanced about 3/4 of a degree. I backed it up to 1 degree retarded or a total of 1.75 degrees. No more detonation!!! WooHoo. Except I think I lost about 30% of my power haha. Right now the power level is fine for me being a beginner and all.

 

Will the top end last longer with the timing retarded?

Depends on how and how much you ride it. Though much more important, how you maintain the bike. Keep the air filter clean and oiled and the transmission oil changed frequently.

 

I personally only mess around on mine. I have no desire to ride competitively, although I have taken it on a smaller track and had some fun, but I'm far from a good rider and just enjoyed the berms and mild jumps. I also have a flywheel weight and really enjoy the extra tractor like feel and less twitchy throttle. I spin the rear all the time I don't know how you guys w/o one even ride these things! lol. 

Glad to year you got her going man. Good luck. 

Edited by Gottadog

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