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Old 06-09-2014, 08:40 AM   #1
HanShotFirst OP
Adventurer
 
Joined: May 2013
Oddometer: 79
XT 225 cutting out at half throttle

1999 Yamaha XT 225
This may be kind of a long post, but I want to give the experts all the data on this bike to perhaps help diagnose what's going on.

Symptom:
Cold - Idles okay, just a touch rough but it will idle. Twist the throttle about 1/3 and she cuts out. Twist it all the way, she takes off and runs smooth.

Warm - Twist throttle half way, she cuts out badly and it just gets worse as it warms further.

What makes it worse
Gets noticeably worse when I ride it off road.

What makes it better
Cooling off, is the only thing that makes it ride better.

Background
This bike was a barn find, 1999 XT 225 that I found in Arkansas. The bike had been ridden to death by a teenager who rode it until it stopped, and then put it in the barn; it was there for 6 years. Believing it stopped due to a fuel related issue, I took a chance, traded the guy a .22 pistol he wanted that I was into for cheap, and took her home. Cleaned up the entire fuel system, new spark plug, new battery, she fired right up and ran like a top.

Moved to Nevada
I'm now at just under 5,000ft elevation, so I suspect the issue while running cold may have to do with the need for a slightly larger primary. My KLX 650 needed a larger primary when we moved here, so that makes sense.

What have I done thus far?
From the time of he move (September) until now, it has sit and dumb me I forgot to drain the fuel. So I took the carb apart and made sure everything was clean. The primary was clean and I could see daylight through the pilot hole, but it does seem to be a VERY small diameter. The secondary (needle): There was grime on the upper part of the needle so I cleaned that off, and verified that I could see daylight through all the holes on the jet. I noticed the float somehow was way out of adjustment; it was way too high. So I put that in order with the hopes that it would fix the problem, but no dice. So everything seems to be in order with the carb, or at least I think so.

A question of valves???
So I have no idea if the valves have ever been adjusted on this bike, I tend to think they haven't because the guy who owned it prior didn't know squat about working on bikes. So obviously this needs to be done, but I'm wondering if this would cause the problem?

I just tend to feel this is somehow a fuel problem, because it just feels like once you crack the throttle, it's being either starved or cut off.

Thoughts from the bike repair Yoda's?
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Old 06-14-2014, 04:40 PM   #2
NicholasDM
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Joined: Apr 2014
Location: Sandy, OR
Oddometer: 8
As somebody else who reached out to this community about XT runability issues and got no replies after days of waiting, I feel your pain. :(

I'm no expert, but I'll take a stab at it from my many years of working on my own vehicles and understanding of carbs. Hopefully something might help! And please forgive my long response; I tend to get wordy.

Quarter to third throttle is where the pilot, slide profile and needle jet all interact as you move from one working range to another. If you're confident that it is 1/3rd throttle, that'd put your carb operating pretty much smack in the middle of the medium speed range where the needle jet and slide cutout provide your F/A mixture. It's also just about where your main jet *just* barely starts to become involved.

First and foremost, I'd check your plug. Is it ashen white? Way too lean. Sooty black? Way too rich. If it's sandy-tan colour, you've got a good mixture.

Second, I'd make double, triple and quadruple sure that there are no vacuum leaks. Even the tiniest (and I mean pin-hole-sized!) air leak can create huge runability issues at different ranges and you'll be forever chasing real problems ten different ways created by a leak. I actually ran into the same problem recently when I was asking about my XT250. Part of the issue was a vacuum leak at the carb boot gasket that was solved with some gasket dressing gunk.

My thinking is that you've got a passage partially blocked or a bit of crud moving around in there or the PO messed with the jets (I've seen some gnarly jets that have been drilled or wallered out). If I had to guess, I'd dig in to the pilot circuit first. Though realistically, if I were in your place I'd strip the carb and rebuild it using all new gaskets, o-rings, jets, needle, etc... Especially having sat in unknown conditions in a barn for years. I know you said you went through it, but unless you used a rebuild kit you're at the whim of those old parts; crushed/dried up gaskets and o-rings, jets of unknown condition, etc... For $30, a rebuild kit is worth it's weight in gold! Rebuild kits come with all of the o-rings, gaskets, needles and jets you need to return everything to factory stock conditions. I'd also strip the carb totally and drop it in a bucket of Berryman's for five or six hours, then rinse, dry, rebuild.

This doesn't sound anything like valves being out of adjustment. Valves out of adjustment would net you any number of the following; backfiring, poor compression (valve hanging open), poor power, poor fuel economy, ugly sounding tapping/rattling noise from the top end... and there are other symptoms that just aren't coming to mind. Interference would be another one, but you'd KNOW if that happened 'cause your top end would be in rattly pieces.

In closing, I think your last statement about the runability problems is very important. By it stumbling and wanting to die just as you crack the throttle, that really does reinforce my idea that it's pilot related. EDIT: Also check your fuel air screw to make sure it's set right. It plays a huge role in idling and coming off of idle. Too lean and it'll choke. Too rich and it'll stumble.

I may be completely off-base, but that's what it sounds like. Best of luck. Please let us know what you find out as it would very helpful to some of us.

NicholasDM screwed with this post 06-14-2014 at 04:45 PM Reason: More info.
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Old 06-14-2014, 06:36 PM   #3
prsdrat
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Joined: Sep 2008
Location: San Diego, CA
Oddometer: 613
Check in over here... http://advrider.com/forums/showthread.php?t=178968

and ask around. Lots of help here.
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Old 06-15-2014, 07:56 PM   #4
rpcraft
Adventurer
 
Joined: Sep 2013
Location: DFW
Oddometer: 65
It seems like from the factory the XT225 was jetted really crappy, after about 1988 to meet EPA standards. I'm currently tweaking mine a little but I am pretty much sure I know what my issue is. I overjetted the main on a rebuild, simply because I shredded the stock main getting it out (talk about a huge pain in the butt). Gonna be a few weeks until I finally get it sorted (traveling with work and stuff) but I'll try and report back once I get it finished to give you an idea of what I did to get it running well. Mostly, my solution for right now with it running rich on the main jet is to pull the snorkel out and that has made an improvement but I can tell it needs to be jetted down still on the power pulls. I'm going to go with the half size larger main jet (127.5) and on the pilot jet I am currently running 42.5 (and plan on leaving it). It currently has the 130 and 42.5 and it starts and idles upon start-up so much better. I am getting some bogging on full throttle and it's just lacking top end power but I think the jet swap will fix my issue without having to fiddle with the Needle setting. Elevation around DFW is only 400 or so feet so maybe that can help you a little in your endeavors.
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