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Jekyll and Hyde performance

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I purchased a new 2012 wr250f this past winter. The following is the list of mods so far...

JD jet kit

185 main

Stock pilot (not sure what comes stock)

Red needle 4th clip position

42 leak jet

JD fuel screw

Merge Racing accelerator pump spring

Yamaha AIS removal kit and throttle screw

FMF powercore 4 muffler

Grey wire mod

Removed airbox snorkel

No-Toil Hi Flo air filter

After all the mods, the bike ran fantastic. No bog or hesitation, clean power throughout the rev range. I did experience a slight "stutter" while holding a constant speed during road riding, but I've read that is to be expected, and it never was more than just a faint stutter. Quickly opening the throttle would pull very hard without any bog or hesitation, and it would accelerate well beyond the 70mph mark. It never bothered me enough to try and resolve it.

Until this last weekend, I had done all of my riding on dirt roads, trying to follow the oem break-in procedure. This was in southeastern Michigan around 600-700 ft elevation at 50-60 degrees.

Friday and Saturday I went riding in northern Michigan at around 1250 ft elevation at around 65 degrees. On this trip, I experienced erratic performance issues. In the first part of the day we were on slower speed tight single tracks. The bike was performing great. Later in the day however, when the trails opened up for higher speed riding, the bike started to stutter and hesitate a lot at around 1/4 to 1/2 throttle. Cracking the throttle would produce no power, constantly sputtering while barely allowing the bike to get past 25-30 mph. Thinking I might be running too rich, I started to play with the fuel screw. I ended up with it turned all the way in without much improvement. It always idled fine, and never stalled, but just wouldn't produce any power.

To get back to the trailhead, we had to get back on the tight lower speed single track. After limping along for a few minutes, the bike started to run well again, and continued to run fine for the rest of the ride, even with the fuel screw turned in all the way. This is the part that is confusing to me. If it's a jetting condition, why is the performance so on and off. I would figure it wouldn't go back and forth between running great and running horribly.

Just trying to theorize, could the faster speed riding have caused the bike to heat up more, thus affecting the the jetting? My first thoughts for corrections are a smaller pilot jet, (due to the fact that it ran with the fuel screw turned in completely), as well raising the needle clip (dropping the needle).

Sorry for the long winded question, but I wanted to explain the problem in entirety. If possible, please offer some suggestions on pilot jet sizes, which JD needle (red or blue), needle clip position, and/or anything else that could be causing this Jekyll and Hyde performance.

Thanks for your support.

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that doesn't sound like jetting to me. It sounds either electrical or water in fuel or crap in the fuel getting stuck in jets.

Just my opinion.

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Thanks for the feedback oldnbold, you bring up an interesting point. The first time I experienced this behavior, it was raining with lots of deep puddles on the trail. The next morning I powerwashed the bike and shortly after that I had the issue again. If water could be the culprit, where should I look for the intrusion?

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I agree with oldnbold.  Drain the float bowl into a cup and see what you get.  And pull the fuel line and drain some too.  I've read that water can get into the carb through the vent hoses.  They all come out in the same place and that moving one or more to a higher location helps.  Pull apart all the electrical connectors and see if any are wet inside. 

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I had a few minutes this weekend to follow the responses and emptied the float bowl. Upon inspection, some sand, water, and other debris somehow found its' way into the float bowl. I'm assuming it was through the vent lines like "flyandride" suggested.

I went ahead and ordered a vent line filter (7602 racing) in hopes of preventing this from happening again. I'll be pulling the carb off soon to fully clean it out and run the new vent lines and filter. While I'm in there, is there anything I should inspect on the engine side? I'm hoping the debris stayed in the float bowl, and I plan on changing the oil, but I'm wondering if there's anything else I can check to confirm that this issue stayed contained to the carb.

Thanks again for the good advice.

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I'm not sure if the Slavens carb filter will stop water from being sucked up (their website is a bit ambiguous about water).  One free mod that my bike came done with (I bought it used) was that some of the carb hoses were rerouted to my airbox.  Here's a link describing what was done:

 

http://www.thumpertalk.com/topic/20000-re-routing-carb-breather-pipes/?hl=%2Broute+%2Bcarb+%2Bhoses+%2Bto+%2Bairbox#entry130830

 

I'm not sure if it's applicable to your '12 as mine's an '04.

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ImageUploadedByThumper Talk1401671204.897316.jpgImageUploadedByThumper Talk1401671221.046645.jpg

After finding the sand and water in the carb bowl, this is the only solution I could find. Here's the filter installed. The blue lines run up and under the tank to act as a snorkel if all of the other lines become submerged. I guess I'll have to wait and see if this works...

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