First ride on a new-to-me YZ250, a couple issues...

I picked up a 2007 YZ250 in the late winter and FINALLY have gotten the thing out for a quick ride after taking care of a bunch of maintenance items.

 

A couple of issues I noted...The bike seems to stutter before coming on the pipe, and then once it does, it hits pretty hard... In neutral if you rev it at all it seems to bog at any more than about 1/4 throttle. The carb and jets were completely cleaned when the bike was down being serviced.

 

Secondly, the rear tire seemed to spin excessively (not hook up) while riding through a grass field once on the pipe. Tires are pretty good but not great, running at 15 PSI on both... Stock gearing.

 

The top end was rebuilt using OEM parts, power valve was cleaned, and the muffler packing was changed. Spark plug is a new stock NGK.  I'm running Motul 800 2T at 36:1 with 93 octane sunoco. The bike is stock other than a FMF Gnarly pipe. Reeds are stock and were in good shape so I did not replace them. I have not yet checked the timing.

 

The prior owner ran Yamalube 2R at 40:1 and the bike was splooging like crazy. I don't think he was a hard rider - did vet harescrambles   He was running a 178 main jet and a 48 pilot with the needle in the #1 (top) position.

 

I decided to drop the main down one position leaner (175) and put the needle back to the stock #2 position (and changed premix brands) in hopes of getting rid of the splooge coming out of the exhaust. Airscrew is at 1 1/8 turns out as set from the prior owner, and I'm using the 48 pilot. I checked the float height when I had the carb apart and it was within spec.

 

I'm thinking maybe I went too lean on the main, but wanted to get some opinions before I go messing with the thing in the wrong direction...

 

I am at about 700ft in elevation and it's about 75 degrees here, moderate to light humidity.

 

Ideas?

 

A couple other notes: I don't think the power valves were EVER cleaned judging from the virgin looking bolt faces (unless the p/o replaced them). They PVs were mostly oily, but otherwise in good shape. Used new gaskets and seals...

 

Also, the muffler packing was absolutely shot and oily. When I took the old packing out, I noticed that the core was probably about 90% blocked with carbon and oil (no, I'm not kidding), which may partly explain the excessive splooge (and loudness).  I literally had to take a dental pick and punch out every little hole in the core. I must have got a couple ounces of carbon out of the muffler core that had the thing all clogged up! 

 

I have not set up the suspension yet either - 185lb rider with stock springs. That will be next if anyone has some quick pointers...

 

Anyway, I'm happy to be finally riding and just wanted to get some opinions on the jetting and lack of hooking up.

 

Thanks!!   

Edited by Clip67

i have an 06 yz 250 and sounds like your jetting is a little off try to go down to a 45 pilot and put the clip in the middle position. i forgot what my air screw is at but once you get it started tune it to the point where you have a crisp throttle. sounds like if it is bogging before it gets on the pipe its running rich on the low. lean it out a little.

Thanks - I'll go make those changes and see where I am at...

 

Any ideas about the suspension setup?

are you sending it out ? or doing it yourself? personally i had mine done at factory connection they valved it for what i was riding and it works awesome.. probably the best suspension i have ridden on. 

It spins the tire because it has so much power. Sit further back and/or roll onto the the throttle slower.

are you sending it out ? or doing it yourself? personally i had mine done at factory connection they valved it for what i was riding and it works awesome.. probably the best suspension i have ridden on. 

 

The prior owner had a set of heavier springs on the bike (too heavy for me) and had the suspension professionally revalved for hare scrambles and woods riding. I had a friend, who has a suspension / engine hop-up business, put the original springs back in the forks and shock. He set everything back to the middle positions, so I am totally starting fresh.

 

I'm going to try to set the sag tonight and then put all the settings back to stock to see where I am at from there... I plan to do some MX and hare scrambles, so I am interested to see  where I am at so far. Just riding in a field, it feels much to stiff at this point - probably why I am not hooking up so well...

 

What is a good sag setting?

It spins the tire because it has so much power. Sit further back and/or roll onto the the throttle slower.

 I raced MX 20 + years ago on KX250s in the am class so I know they are constantly spinning on the pipe to some degree or another depending on traction...

 

What I am talking about is that the bike is nearly stepping out to the side once on the pipe - not hooking up at all.  I know it is too stiff, just haven't played with the suspension yet, and was looking for a decent starting point...

 

I took some air out of the tires too - running at 12 psi for now.

Edited by Clip67

Do you know if the topend had any porting work done by the previous owner?

 

As far as the suspension, you said the previous owner had it resprung and revalved for his weight and riding.  You only mentioned that you changed the springs back to stock.  The springs and valving work together to make the suspension work for your style.  It may be worth your while to have the valving returned to stock as well, or better yet have the whole thing set to your preferences.

 

For the jetting, my experience has always been to go back to stock on a fresh topend, and make the necessary adjustments from there.  The modern YZ250 should rev crisp without a bog.

Edited by USED YZ426F

OK, I put the 45 pilot in and actually raised the clip position one step to the top (leaner) position. I rode the bike and it made a big improvement, although it is not quite there yet, still stuttering just a bit.

 

I followed Spankey's Jetting guide that is posted in the FAQ and started to play with the airscrew. The bike idles the fastest at about 3 1/4 turns out, so it looks like I am putting the next size smaller pilot jet in it. Luckily, I bought a 42 last time I ordered parts, although I am kind of surprised I have to go this low...  

Do you know if the topend had any porting work done by the previous owner?

 

As far as the suspension, you said the previous owner had it resprung and revalved for his weight and riding.  You only mentioned that you changed the springs back to stock.  The springs and valving work together to make the suspension work for your style.  It may be worth your while to have the valving returned to stock as well, or better yet have the whole thing set to your preferences.

 

When I put in the new top end, I did not notice any porting work done to the cylinder, and in fact I noted a good bit of sloppy casting still around, so I am pretty sure that nothing was done to the motor other than the addition of the gnarly pipe.

 

Yes, I know I may end up revalving it again for me, but figured I should ride it a while to see where I am at. I'll probably end up compromising a bit between MX and the slower hare scrambles as I will probably do both with the same bike...

 

Thanks!

It sounds like you have been down the same road I have jetting wise.   My jetting work really helped but it was still not quite perfect.  Did you check your timing? Detonation might be causing the remaining stuttering like mine was,  Check out this link:   http://www.thumpertalk.com/topic/584339-yz250-timing-thread/    carver really knows what he is talking about this has made my bike awesome.  Still haven't tried all the options yet but my bike is much better running after my timing adjustment.   

Edited by greenejr

It sounds like you have been down the same road I have jetting wise.   My jetting work really helped but it was still not quite perfect.  Did you check your timing? Detonation might be causing the remaining stuttering like mine was,  Check out this link:   http://www.thumpertalk.com/topic/584339-yz250-timing-thread/    carver really knows what he is talking about this has made my bike awesome.  Still haven't tried all the options yet but my bike is much better running after my timing adjustment.   

 

Thanks for the link. No, the timing is the one thing I have not looked at yet. I have the new gasket to check it, but have to order the tool. I'm going to try to get the jetting close while I am waiting on the tool to ship. I'll probably retard it a degree or two after checking it.

 

I'm a little surprised that the jetting is this far off on the bike. When I test rode it before I bought it back in the late winter, it seemed to run strong with the owner's jetting. But then, it was winter and he was running a hotter plug, many parts were worn, not to mention all the splooge coming out of it with the yamalube he was using.

 

Live and learn I guess!

Yeah, mine was with stock jetting which was way too rich...I had bogging with throttle on bottom and top.  Also fowling plugs left and right. I leaned out the pilot and main jets and lowered my needle but still had some stumbling and I retarded the timing 2 degrees and it is great now!!  Been thinking of getting a gnarly pipe like yours next!

Interesting jetting prob. When Im running an open silencer I use a 50 pilot and 170 to 172 main But I dont ride very fast when I have the spark arrestor in I run a 48 pilot with a 168 to 170 main originally it had a 50 pilot and 175 main spooge city. My fuel oil mix is 40 to 1 super unleaded gas

Anyone else running Motul 800? I thought it was interesting that the mixing ratios on the motul bottle, used 66:1 and 50:1 as mixing examples. Seems a bit light on oil to me...

 

I'm running 36:1 right now and see just a hint of oil at the exhaust pipe tip, and little smoke before it got up to temperature. This was with the 45 pilot, and I'm going to try the smaller size, hopefully tomorrow....

JD jet kit red needle,,just do as the kit says,,,all will be good :ride:

Anyone else running Motul 800? I thought it was interesting that the mixing ratios on the motul bottle, used 66:1 and 50:1 as mixing examples. Seems a bit light on oil to me...

 

I'm running 36:1 right now and see just a hint of oil at the exhaust pipe tip, and little smoke before it got up to temperature. This was with the 45 pilot, and I'm going to try the smaller size, hopefully tomorrow....

I think your going in the wrong direction. Pilot is fine try stepping down on the main jet 1 size

Motul 800 has a very high flash point. I wouldn't run that in anything over a 125. I'd also go back to 32:1, which will actually lean out your AF ratio a little, helping the spooge problem. I'm not sure why it's studdering, maybe it's old gas, or maybe you cleaned the carb a while ago and it needs another cleaning? Clean all the circuits too, not just the brass bits.

I think your going in the wrong direction. Pilot is fine try stepping down on the main jet 1 size

 

OK, I'll try that first and see where I am at.

Motul 800 has a very high flash point. I wouldn't run that in anything over a 125. I'd also go back to 32:1, which will actually lean out your AF ratio a little, helping the spooge problem. I'm not sure why it's studdering, maybe it's old gas, or maybe you cleaned the carb a while ago and it needs another cleaning? Clean all the circuits too, not just the brass bits.

 

The gas and premix are new. I thought I did a pretty good job of cleaning the carb when it was off, but I can always go through it again while I am making changes...

 

Things did get better when I changed the pilot, but it is still there to a lesser degree. What kind of oil do you recommend? Going to be doing MX and hare scrambles...

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