New XR650R "misses" occasionally

My new '02 XR650R has 625, 85% dirt miles on it. It came from a notable Honda dealer set up with the Honda Power-up kit installed.

I put a UNI air filter on and removed the backfire plate. I have not adjusted anything. The needle is supposedly in the stock position.

It "misses" when I roll the throttle on over fast choppy terrain at lower RPM's. The jet is a #168 for the 4,700 to 6,000 foot elevation I generally ride, although it can extend to 10,000 plus feet. It generally runs flawlessly, especially at higher elevations and on smoother ground. I have been told by one Honda shop that this jet is too lean and another Honda shop says it is perfect. The sparkplug tells all and is burning light tan with a dusting of carbon indicating a good jet, no? The majority of my riding is at the lower elevation.

What do you think is happening? Thanks in advance for your tips. :)

If the problem is only happening over fast choppy terrain, then you may want to double check the float drop to make sure its setup within specification. Another thing to check is to make sure you have the white plastic shroud around the main jet. It easily falls out and some guys just trash them and think they don't do much, but it does have a purpose. The white plastic shroud traps fuel around the main jet to minimize it from fuel starvation under hard acceleration or on choppy terrain, etc. The last couple things that comes to mind is to make sure your decomp adjuster is within spec and to double check your intake for air leaks. Just twist the carb around a bit to see if it will move and then tighten up the clamps to make sure they are tight enough. You should not have to worry about running too lean with a 168 at thsoe altitudes and in fact you may find it to be too rich, but the color of the spark plug won't tell you the whole story. Also, the spark plug will only accurately show you what's been happening with your engine during the last few seconds you shut it off. In other words, if you shut your bike off while it was idling, then the spark plug won't accurately reflect what's been happening at half throttle or at wide open throttle while under load.

I ride around 1400 ft. and my bike ran better with the stock pilot. The color of the tip of the tail pipe tells me more than the spark plug.

Hi RWilson,

Got a couple of questions for you.

1) Have you tired going through the choppy stuff with a steady throttle, say in third gear (lower RPMs) and get the same result/miss?

2) Have you tried: starting the bike, leaving it in neutral, roll on throttle as you would in choppy stuff and having someone bounce the bike to see if you get the same effect? Look for possible gas overflow from carb (gas would come out the overflow tube near rear wheel).

3) Have you checked for loose wiring a) under the seat, b)possible abrasion of ignition (high tension wire) under the fuel tank along the right side the frame and 3) a good seating of the sparkplug wire?

The main jet size is fine. I run a 172 main at 4700' because of sand (better response under load). You said the needle is in stock position. Most people (including myself) have found that the middle (3rd clip) position is best.

The most common problem is as Qadsan pointed out, float level.

Good luck

First, you're main jet is fine, if not a little rich. I run a 160 in Colorado with excellent results and no overheating even on steep, slow trails. Second, if the needle is set to stock position, that is not correct with the power-up items in place. If you're running the competition needle and seat, then it should be set in the 3rd (middle) position. If you're running the stock needle, it should be in the 4th (down from top) position. Stock position is too lean, which is 2nd from top.

Next, slight missing over rough terrain could easily be a result of the float bouncing around. I doubt this unless the bike is being run at high speeds over deep whoops. The main jet has a splash guard around it, as well as baffle plates in the carb body to help prevent the problem. Still, it's a possibility and it does happen.

Finally, never trust or believe the Dealer. If you want something done right, do it yourself. They are complete idiots if they said it's "jetted too lean" with a 168 main jet at such a high altitude. That's absurd! In my opinion, at elevs over 6000', the bike runs strongest, without getting hot or scorching the plug, with a 160 main jet, and ALL of the correct power-up items in place exactly as they should be. Good luck with it!

L.L. :)

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