Strange (to me) problem with 03 YZ250f

[robwbright]

Ok - bought this YZ250f - was getting coolant in the oil, but actually ran pretty good, save for the white smoke. Before I realized the coolant leak was there, the bike started easier than my personal YZ250f - and my bike starts almost as easy as a 2 stroke.

We tore it down and discovered that the prior owner had reused the head gasket AND left out the O-ring and "water pipe" that go between the crankcase and the cylinder.

Thus the coolant in the oil.

We checked the head and cylinder to spec, put new rings in it and reassembled (with all the parts in the motor this time and with the necessary new gaskets.).

The bike was really hard to start after the rebuild. Once we finally got it started (using WOT), it quit after about 4 seconds. A few more kicks, it started again, but felt like it wanted to quit.

Took it for a ride in the yard and up the road and back. Bike was really strong on the bottom and pulled well thru the range. Did feel like significantly more engine braking on decel than my personal bike has.

Idle was WAY off, so worked on adjusting it. Got the idle absolutely perfect, the bike would sit there and idle with no issues whatsover.

Turned it off, started up again 1st or 2nd kick 3 or 4 different times. Was backfiring a bit on deceleration, but nothing too serious, IMO. Figured it was just a jetting issue.

Loaded it up and brought it back to my house and left it in the garage overnight.

I just spent 3 hours in the garage trying to start it. Will not start. Almost did a couple times using WOT, but wouldn't even come close to firing off in any other way. Did get a couple of significant backfires that echoed through the neighborhood.

Cleaned the carb as well as I could.

Fuel screw has been played with between 1.5 and 2.5 turns out.

Raised and lowered the needle clip (for what that's worth).

Two different plugs are getting spark.

Float seems to be working properly.

Could I have just flooded it out badly from the start and never recovered? (I'm baking the spark plugs right now).

Jetting problem?

Or is it most likely a valve issue?

I didn't think it was the valve issue because of the fact that it ran well (all things considered) before the rebuild and ran well and started easy hot after the rebuild.

Any help would be appreciated.

 

[IndyMX]

I am by no means an expert at all, but it would seem to me that if it's trying to start WOT cold, then the pilot circuit must be crazy rich..

I could be completely wrong though. Maybe a clogged leak jet??

 

[robwbright]

Crazy rich is my father in law's educated guess, as well.

Just really strange to me that it wasn't like that before - but I guess the carb could have gotten something in it while we were rebuilding.

 

[robwbright]

Then again, maybe it was crazy rich and the coolant in the cylinder was "leaning" it out. . . ;)

 

[IndyMX]

Then again, maybe it was crazy rich and the coolant in the cylinder was "leaning" it out. . . ;)

If the cylinder was leaking coolant, it's possible that air was getting in too and leaning it out.

I'd tear down the carb again and make sure all of the passages are blown out good.

Did you take the cover off the Accelerator pump?

Very possible it's just a chunk of dirt lodged in there some place.

 

[nikki]

Assuming you had the head off while working on it... might want to pull it again and just check the valve clearances at TDC. We put a top end in my '03 YZ250F once, and had a shim get wedged under the valve cap, and not sit in the groove, and couldn't figure out why it wouldn't start, and finally figured that out.

Might not be your issue, but it only takes about 30 minutes to confirm the clearances are in spec... and then you can rule out valve issues for now.

 

[robwbright]

There was a piece of dirt in the Accelerator Pump. The AP was not squirting at all. Thus, no start.

Cleaned the AP, reassembled and it started right up.

Thanks

 

[IndyMX]

Most excellent! I love an easy fix.

 

[robwbright]

Most excellent! I love an easy fix.

Thanks for the input before - it was your recommendation that got me to take a closer look at the leak jet and AP.

Easy fix? Yes. The blister on my foot from kicking on and off for 3 hours the night before? Not so easy. . . ;)

 

[IndyMX]

Thanks for the input before - it was your recommendation that got me to take a closer look at the leak jet and AP.

Easy fix? Yes. The blister on my foot from kicking on and off for 3 hours the night before? Not so easy. . . ;)

Umm.. 10 minutes no start, I start looking for the problem..

3 hours?? Wow.. you're just stubborn.

 

[robwbright]

Umm.. 10 minutes no start, I start looking for the problem..

3 hours?? Wow.. you're just stubborn.

"Kicking on and off"

Interpretation: Kick it 15-20 times with varying degrees of throttle and choke. . . stop (sometimes cuss), pull carb, clean, put on carb, kick again, check fuel, kick again, pull plug, clean plug, put in plug, kick again, pull plug, spray crab cleaner or gas directly in cylinder, put in plug, kick again, remove carb, change needle clip setting, put on carb, kick again, etc. . . etc. . .

Never did get around to disassembling the AP until yesterday, though. . . in part because I didn't know how that worked.

Still learning about these 4 strokes. Haven't had a problem with the AP on my personal bike.

 

[IndyMX]

I went thru a similar situation with my brothers KX250F early last year..

Could not get that pig to fire for anything...

Finally sent it out to have someone else look at it, I had busted my knee up pretty good by then..

It just so happened that the guy we took it to had experienced the same problem on a KX250F before.. The cam gear had moved on the cam. So he moved it back to where it's supposed to be and tig welded the little ******* in place.

I don't understand why they don't just do that to begin with.. Oh well, I'm sure there's a logical reason.. I'm betting Rich would know.

 

[robwbright]

You're assuming these companies are always logical. . . ;)