Tuning help

I need a little help here gang

I was out riding my low mileage XR650r Sunday when it started to run very poorly.

This is a stock uncorked and was running fine for the first 120 miles.

Cruising at 55 it was back firing and surging.

At idle everything seems ok as you twist the throttle it start running very rough.

Though it will rev up and runs better w.o.t.

I have since cleaned the carburetor and checked the plug.

The plug is very black.

It is running better now just when I blip the throttle it is puffing black smoke.

Any thoughts on what I should check next.

Thanks Matt

Change your plug. Maybe you just have it running rich and it is fouling your plug. What main jet are you running?

Have you done any maintenance/mods lately? Is the air filter over oiled or clogged with dirt?

If its not your jetting or air filter....

How is your choke? Sounds like something is cutting off your air flow (intake or exhaust ) or something in your carb is allowing more fuel to flow (Loose jet? Did you tweak with the jets lately?).

Should have a new plug today.

Air filter was clean to start the ride.

I installed what ever the uncork kit was new needle, pilot jet and a 168 main jet. Removed all the plugs and drilled the sparky. Manifold was also changed.

I reset the floats last night still not running right.

I am going to a 165 main next with the new plug.

Supposed to do a 500 three day weekend ride. I really need to figure this out.

Billahjack I think you are right about over oiled air filter.

K&N and I don't really like it.

The new air filter will be foam as soon as it arrives.

So much easier to change on the trail.

For only 120 miles in the dust the filter looks very dirty.

K&N sucks for dirt use. OK for street only applications but I still prefer UNI. If you get a UNI, you can carefully remove the metal cage from the filter to oil and clean it. You can also remove the backfire screen in the airbox of the bike, although there is still possibility of burning the filter when you backfire. I have done this.

I like the No-Toil system as it is a little bit better for my health and the environment, but good old fashioned filter oil then cleaning with gas still works well too. Make sure not to wring out your filters when cleaning and oiling, they will come apart. Just ball or roll up and squeeze.

Your main jet might be a bit small if you are near sea level. You can use a 172 or 175 at sea level to about 1500 feet, 170 or 172 from about 1500 feet to 3000 feet elevation.

I change my spark plug about twice a year since riding is year round here in California.

Try the WWW.XR650R.US jetting page if you have not been there yet.

Excellent advise

I cleaned the air filter and installed a new spark plug voila everything is good again.

Guess I cleaned the carb just for the practice.

I live at 3500 and most riding is higher once you get out to the mountains after the snow melts.

I am trying to set it up for about 4000-5000 feet so it will be a little leaner getting in and out of town.

Then it should be pretty close for the trails.

Just installed the 165 and will bring the 168 and 170 on my 500 mile loop tomorrow.

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