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Mile-high jetting question

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Hey all,

 

New XR owner here. I picked up an '02 XR650L with 7400 miles about 2 weeks ago from a nice guy up in Fort Collins. Bike was COMPLETELY stock from what I can tell. It has the stock muffler, and even had the smog crap (I pulled that off right away!). He had removed the stock air filter (still had it) and installed a K&N, but he had not taken the snorkel out. Dave's mod has not been done

 

So here is my question. I have searched around the web for about a week now, looking for other owners that have been in my position. I am wanting to desnorkel, maybe put a UNI in, and go with a DG-O series with a quiet insert. I will be consistently riding around south Denver (5200 ft), but have quite a few rides planned up to the mountains, which range anywhere from 8,000-10,000 ft offroad trails, to the peaks of Mt Evans and Pikes Peak. As far as I know, it also has the stock jetting, which wouldn't surprise me. From my understanding, the higher in elevation you go, the leaner your jetting should be. The bike runs flawlessly as it is, it never stumbles, bogs, or sputters. Also, I know that desnorkling and after market exhausts cause the bike to run even leaner.

What jetting do you think I should run with these mods? 

 

I found a guy online in a similar position to mine, and he was running 155/52, would this be a good starting point? 

I also plan on doing the modification to the adjustment screw, but don't quite understand how that would affect the bike with what I will be running.

 

Afterthought: If I grind the header welds, would this also cause the bike to run leaner?

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I'm in Colorado Springs...

I have many of the same desires to complete the XRL breathing upgrade. I've completely desnorkled, desmogged the bike, added a UNI filter, played with a couple of jetting configurations and all of Dave's Mods. The only thing that remains is upgrading the exhaust (still completely stock).

I've not been up Pikes Peak or Evans (plan to) so my test isn't fully complete but I'm pretty satisfied with a 58 pilot and a 160 main. This may be a little rich but it did run great on a ride between Woodland Park and Pine (8,000 feet?). I may try a 158 main.

Rog

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Hey all,

 

New XR owner here. I picked up an '02 XR650L with 7400 miles about 2 weeks ago from a nice guy up in Fort Collins. Bike was COMPLETELY stock from what I can tell. It has the stock muffler, and even had the smog crap (I pulled that off right away!). He had removed the stock air filter (still had it) and installed a K&N, but he had not taken the snorkel out. Dave's mod has not been done

 

So here is my question. I have searched around the web for about a week now, looking for other owners that have been in my position. I am wanting to desnorkel, maybe put a UNI in, and go with a DG-O series with a quiet insert. I will be consistently riding around south Denver (5200 ft), but have quite a few rides planned up to the mountains, which range anywhere from 8,000-10,000 ft offroad trails, to the peaks of Mt Evans and Pikes Peak. As far as I know, it also has the stock jetting, which wouldn't surprise me. From my understanding, the higher in elevation you go, the leaner your jetting should be. The bike runs flawlessly as it is, it never stumbles, bogs, or sputters. Also, I know that desnorkling and after market exhausts cause the bike to run even leaner.

What jetting do you think I should run with these mods? 

 

I found a guy online in a similar position to mine, and he was running 155/52, would this be a good starting point? 

I also plan on doing the modification to the adjustment screw, but don't quite understand how that would affect the bike with what I will be running.

 

Afterthought: If I grind the header welds, would this also cause the bike to run leaner?

 

I have not performed any of the mods you describe and am at the same elevation (5,000 feet).  The stock jetting works well for me.  I would be careful going too rich.  I've tried reading the plug but with ethanol in the gas and all the other goodies, reading plugs is difficult these days.  155/52 does not sound too far off the mark for the mods you are proposing at that elevation but would likely be rich for 8,000 - 10,000 feet.  Unfortunately, the only real way to be sure is to weld a bung into your header and use a wideband sensor coupled with various riding conditions.

 

I welded a bung in mine and THINK you can get away with a narrow band.  Any serious racer/tuner will say that I am crazy but my logic is grounded in this:

 

1)  The pilot can be dialed in fairly easy, screw it in until it dies, screw it out until it runs rough, somewhere in the middle is where you want to be.  If you can screw in the pilot without the bike dying, then you are too rich.  If you have to go out more than 3 turns, you are probably too lean.  It is not any more complicated than this.

 

2)  A narrow band sensor will not give you as accurate information as a wideband BUT can give you a FAIR idea of whether you are rich or lean at the 1/4 - WOT area.  Plus, they are cheap...

 

Does anyone in your area have a dyno?  I'm going to have to try the narrow band this weekend just to see if it works...

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At 8,000 feet you need about 93% of the A/F at sea level (0.93 x main jet size).

At 10,000 feet you need about 92% of the A/F at sea level (0.92 x main jet size).

You should also raise the needle clip up one notch to address midrange mixture.

 

Since you've done some other modifications all that goes out the window.  I suggest you try Mikuni's Roll-Off method:

"Roll-off Method:
This method is a good way to get the main jet either correct or within one size of correct. It is based on the fact that that as the throttle is closed, the air/fuel mixture richens momentarily. This normal enrichening can be used as a diagnostic tool. The test is started with the engine running at an rpm high enough to ensure that it is “on the cam.” Open the throttle fully and let the engine pull for several seconds. Then, quickly close the throttle to about the 7/8ths position. If the engine seems to gain power, the main jet is too small (lean). Fit a larger jet. If the engine hesitates as the throttle is rolled off, the main jet is too large. Fit a smaller one. When the main jet is correct,  the engine will continue to run smoothly and evenly as the throttle is closed. Note that a main jet that is far too rich or lean may cause the engine to misfire at full throttle."

Edited by VortecCPI
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