08 YZ250 doesnt want to pull hard

I have every reason to believe the bike is running rich in the mid to upper. Example 2nd gear big hill climb I can get up in the revs and accelerate hard to start but then the bike quickly looses power during the climb forcing me to downshift to first and I am still on the throttle hard. I dont want to finish a hill in first or downshift to first I want to continue hammering the throttle and if anything upshift! :thumbsup:

Float height correct

32:1 Castor 927

New top end - noticed prior to latest top end

JD Jetting

172 main -

45 pilot

Red needle one step leaner than JD's recommendation

Boyesen Rad valve

sea level to 3k feet

Plug at last top end looked fine and I do think the bike is running slightly lean at idle (surges) but pulls hard down low and doesnt stumble or do anything silly.

I have not done a plug chop but was going to drop to a 170 main and see how that felt. It is warmer now I know and when the thing starts to bog down and stop making power it gets pretty smokey.

Am I going in the right direction here thinking shes rich on the main?

I think in the past I have just dealt w/ it but as I am continually picking up speed I need all the power this bike can offer at times thus the need to get the jetting tits.

Thanks all

I do not think you are too far off on your jetting....at least not enough to make it fall flat. I would toss a comp test at it, install a new plug and see what that does for me.

is it possible that you have a plugged up main and it is so lean it won't make power?

Def. sounds like the best place to start. I dont see how you should be bogging in second, I actually never use first because I lose traction before the bike will ever think about bogging.

I do not think you are too far off on your jetting....at least not enough to make it fall flat. I would toss a comp test at it, install a new plug and see what that does for me.

is it possible that you have a plugged up main and it is so lean it won't make power?

Well new top end has about 4 hours on it and its similar feeling to the last top end. I dont suspect a lack of compression here.

If I had a partially clogged main and the bike was lean up top (which may be the issue) would I be leaving a huge blue smoke trail when it bogged down if lean?

Not neccesarily, I pulled the plug after my buddy fried his top end on his 125 from running lean to the extreme and his bike never seemed to smoke. It did smell like it was on fire though (says he got his mains mixed up durring installation) but Im thinking he thought he had it dialed in since it ran like a raped ape.

no, they typically will not smoke like that when too lean. I would still go with a new plug, and fresh fuel. check the jetting, I have seen them numbered wrong....that was fun:bonk: I have seen guys chase their tail and it turned out to be poor fuel too.

I have to ask this question.....do you have a spark arrestor on the bike. Reason for asking is, it may be plugged up. Unless I'm missing something here. You didnt mention anything about exhaust.

If your near sea level, you should be at a 178 on the main and I think a 50 for pilot, That is stock, I run 168 main and I think 45 or 48 pilot because I am in CO at 4600 ft and up.

I have a 2010 YZ 250 and I am pretty sure the stock carb and settings are the same as the 08, but double check yours and what they should be, because you might be running a little lean with that smaller jet.

What color is your plug after riding it hard?

Also you might want to try your gas/oil ratio a little leaner. I run Yamalube at 40:1 and never have problems. Yes running your 32:1 would give you more lube, but also takes away gasoline making the burn leaner, not richer.

less oil also means lesser ringseal, the oil helps to seal the rings. The harder you ride the you also need a more oil to make sure that your engine runs with out problems. How about the timung?

Ok where to start?

Timing is retarded a couple degrees but that was done a long time ago in an attempt to help tractability in the slick slick stuff. Bike ran very well in the past w slight timing retard.

Yes the bike is spark arrested. Turbine Core II if I recall correctly.

I dont want to change my mixture to troubleshoot a jetting issue. The issue isnt Castor 927 or 32:1. Yamaha manual calls for 28:1 Yamalube if I recall.

The bike has run very strong in the past w/ the same jetting.

I ride the bike every weekend so the freshness of the gas is a non issue.

I will try a new plug. My problem is I dont really have the time to fiddle w/ this thing in the woods. It seems like my riding is all business anymore. Show up. Unload. Get the mileage in. Load up go home. No stopping or waiting really. Maybe I need to sacrifice a day and mess w/ the bike? So I haven't pulled the plug aside from my last top end and it looked fine. But then again I dont necessarily need to look at the plug to tell me somethings not right. The smoke says rich. The lack of revs and power up top tell me rich.

but the sparky is due for another pack. probable have about 100+ hours on the last pack. But wouldnt a clogged sparky give me issues everywhere in the rpm range?

Guys thanks for the suggestions here. I am completely open to everyones ideas even if it may seem like I am not. just trying to help rule out obvious things. :thumbsup:

Hello there

I check the plug after each ride. Since I put a hole into a piston I'm kind of paranoid. The crank seals are hard to catch when they are about to fail, and the consequences are expensive in time and money alike.

An older plug can also deteriorate performance I think, I remember that a new coil on a Chinese bike (my first) did make the bike perform better. A new packed silencer also makes an engine perform better. Since when do you use the same packing, or did you ever change it? Recently I came across a line saying that every 40 hours or so the packing should be changed.

Regards

Arnego2

Yeah I use new packing but I am due for a repack. I will put a new plug in it as well and go from there.

Thanks

I just had a kawasaki come through the shop that had a bunch of money tossed at it. It would do the same thing. It was a bum plug.

If the new plug doesn't solve this problem...try this.

Just had a friend with this problem. Sounds like you could be running out of gas at high rpm.

Do you have a fuel filter in between your tank and carb? If so, take it off or replace it. Check the fuel flow coming out of the tank. (take the hose off and view flow into a container) Check the fuel flow coming out of the carb drain.

Check your transmission oil level to be sure you are not sucking oil through the clutch side crank main bearing seal that would explain the excessive blue smoke that you are seeing. The jetting specs that you listed seem to me to be ok.

Edited by Snipetracks

if it,s smoking suddenly and down on power,with no jetting changes,my bet is a leaking crank seal.

Ok where to start?

Timing is retarded a couple degrees but that was done a long time ago in an attempt to help tractability in the slick slick stuff. Bike ran very well in the past w slight timing retard.

Yes the bike is spark arrested. Turbine Core II if I recall correctly.

I dont want to change my mixture to troubleshoot a jetting issue. The issue isnt Castor 927 or 32:1. Yamaha manual calls for 28:1 Yamalube if I recall.

The bike has run very strong in the past w/ the same jetting.

I ride the bike every weekend so the freshness of the gas is a non issue.

I will try a new plug. My problem is I dont really have the time to fiddle w/ this thing in the woods. It seems like my riding is all business anymore. Show up. Unload. Get the mileage in. Load up go home. No stopping or waiting really. Maybe I need to sacrifice a day and mess w/ the bike? So I haven't pulled the plug aside from my last top end and it looked fine. But then again I dont necessarily need to look at the plug to tell me somethings not right. The smoke says rich. The lack of revs and power up top tell me rich.

but the sparky is due for another pack. probable have about 100+ hours on the last pack. But wouldnt a clogged sparky give me issues everywhere in the rpm range?

Guys thanks for the suggestions here. I am completely open to everyones ideas even if it may seem like I am not. just trying to help rule out obvious things. :thumbsup:

We are in the same boat. I show up and ride. Not a whole lot of time during the week to work on bikes. But. I ran into this before on my Honda CR250. With all the woods riding I do, I dont open it any more like I use to. Found my bike not to rev. Pulled of the muffler to check, found the core plugged up. Enough to run at slow rpms, but would not rev to climb any hills. Just a place to start. Good luck.

Hi

I just remembered one thing that happened to me. It could be that the rings are not seating properly.

regards

Arnego2

Edited by arnego2

Guys thanks a ton for the suggestions. I will definitely report back w/ whether or not the new plug fixes things. First things first I guess.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now