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carburetion problems XT225.


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Hi, I'm new here. Name's Dennis, from Florence, AZ. I have an '02 XT225 that I recently rebuilt the carb on. It was running poorly, and I found the carb pretty dirty. I cleaned it all up, replaced the float needle valve and seat, float bowl o-ring, and float bowl drain screw. The exhaust has had the Z1 mod done to it by a PO (drilling out the baffle) The jets are 130 main, 40 pilot. Pilot screw 2 1/2 turns out. It has run fine before with these jets. When I got it back together, it started right up and idled fine. Midrange is also ok. But it cut out badly on full throttle. After going back through the carb and making sure everything was right, including the float level, it still did the same thing. I also replaced the plug, the old plug showed just slightly rich. I finally removed the airbox cover and air filter (Uni filter) and ran it up and down the road a few times at full throttle. It ran fine. I put the filter and cover back, and it started cutting out again. This would seem to indicate it is running rich on the main jet. But that doesn't indicate how it used to run fine with the same jets. Any ideas would be appreciated. Should I switch to a smaller main jet?

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Thanks. I will try that tomorrow. A vacuum leak was my first thought. I have eliminated that possibility. When I reinstalled the carb, I also replaced the manifold. It was working ok before, but I noticed several small cracks in it. It has the stock clamp, which is not bent. One thing I did notice, is that the new vacuum cap I got with the manifold fit too loose. I replaced it with a piece of vacuum hose that fit very tightly, and put a screw into the other end that also fit tightly. I am convinced that there are no vacuum leaks between the manifold and head, or carb and manifold. I tested it with an unlit propane torch. If there is any leaks, it will suck in the propane, and the idle will go up. It didn't. I also noticed that the '02 XT225 came with a 125 main jet. Mine has a 130. Maybe the PO upjetted to compensate for the drilled out baffles in the exhaust. But still, it ran fine for over 3 years with that jet.

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It looks like I have solved the problem at least for now. I took it for a spin with the filter in place, without the cover, and it still cut out a little bit, but removing the cover helped. I decided to try a 125 main jet in place of the 130. I put everything back together, started it, let it run about 5 minutes while I finished putting the seat on, and took off on it. At first it tried to stall when I opened the throttle. I had to let it run a few more minutes before it would take full throttle. But it runs fine now. Good power, and no cutting out. I suspect it is a bit lean now considering how long it took to warm up. This carb (if it is the original, I have no way of knowing) originally came with a 125 main jet. Somewhere between '99 and '02 they switched from a 130 to a 125 main jet. I don't know if the carbs are different in any other way. But the Z1 mod should have leaned it out at least a bit. 

 

Part of the snorkel is still there. I cut off most of what was inside the airbox, but left the part with the elbow. I'm hoping that elbow will help keep some of the dust out of the airbox. Every time I clean the filter, I also remove what is left of the snorkel, clean it, and coat the inside with grease. It's amazing how much dust that grease catches. My altitude is about 1200 feet. Maybe next weekend I'll take it up to 9,000 feet and see how it does. I may need to jet it somewhere between 125 and 130. I'll keep an eye on the plug and see how it is doing. At least my header pipe is not glowing red. 

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It must be really, really lean to simply not run just by removing the filter and housing(or really congested). Should at least run even without the intake, maybe not great but it should run. may need 120, but higher elevation will be better.

 

It ran fine with the 130, with the filter and airbox cover removed, but cut out badly at full throttle with them in place. Since removing the cover and filter would have leaned out the mixture, it would seem to have been to rich. I replaced the 130 jet with a 125, put the filter and airbox cover back in place, now it runs fine, just takes longer to warm up before it will take throttle without bogging. I have one of those chokes (enrichener knobs) that attach directly to the carb. It starts easily with it pulled only halfway out. It will idle without the enrichener after about 30 seconds. I'm happy with the way it runs, my concern is that it may now be too lean. 

 

I'm also puzzled by it's behavior. I have never had an engine cut completely out from being a little rich before. They are usually down on power, and feel a bit mushy, but this thing was cutting out completely, then coming back, then cutting out again. Just like it was not getting enough gas, or the ignition was being turned on/off/on/off very rapidly. I had even considered an ignition problem, but was convinced it was the carb. 

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When it's idling and warming up it isn't even using the main jet so changing that won't effect it. You might need a size bigger pilot jet or try to adjust the mixture screw(if this model has that ability) Though stumbling at steady throttle is usually a sign of rich condition, but could be lean as well. Let it idle for a while the shut the motor down and look at the spark plug color, that should give and idea of whats going on.

 

I don't think ignitions are a problem with these, they are pretty bulletproof.

Edited by jjktmrider
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