Uncorking The XR600R-Jetting Questions

3 replies to this topic
  • Kawabuggy

Posted February 27, 2007 - 06:00 PM


I purchased a 155 & a 158 main jet, plus a 68S pilot jet today for my '93 XR600R.

I have been reading about all of the uncorking mods for the XR650R, but can not find anything specifically geared towards the 600.

I will be running a Hot Cams-Cam, and a factory exhaust. The guy I bought the bike from has already removed the baffle, end-cap, and spark arrestor. The header is stock, but I plan on purchasing an FMF stainless header, and slip-on later on.

Do you think the 68S will be okay? Which of the main jets should I try first? Are they within useable range with my set-up? If it matters, I am at sea level.. Well, in Houston, I think we are about 20 ft. above sea level.

The bike is not here yet. Once it gets here I will confirm whether or the not the air box has been opened up. If not, I will take care of that straight away. The bike already has a K & N air filter on it. Are there any mods that I need to make to the insulator?

What about drilling the slide? Is that something that is 650 only??? I have been reading about drilling the 2 off-center holes out on the slide.

I have heard that removing the extra welded metal from inside the head pipe is a good step. I will try that until I purchase the after-market header. What type of power increase will the aftermarket header & slip on give after the cam, airbox, and jetting mods?

Any insight or advise that you can offer would be greatly appreciated!

  • wickedsprint

Posted February 27, 2007 - 06:09 PM


Not sure on jets with that bike, but if you have the same carb as most XRs do, get the choke plate from XRs only, gets rid of the little spring flapper that likes to break and find its way into the motor. About 20 bucks.

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  • cleonard

Posted February 27, 2007 - 07:13 PM


Here is another vote for replacing the choke plate. I caught mine just before it broke. It wasn't just the flapper, the whole choke was almost broken in half. I just took it out and covered the hole for the shaft. I can start down to freezing with only a few problems. The method is to tip the bike over when it is cold.
That allows it to "flood" a little. I did pick up a new plate, but I haven't put it in yet.

Drilling the slide is only for the XR650L. The L has a constant velocity carb and the slide is vacuum operated. Drilling it allows it to open faster. The slide on your 600 is directly connected to the throttle so there is no need to drill.

The 68S and 158 should be just about right. I have a 68S and 155 in my XR600, but I ride it higher. Most of my riding is from 2000 to 8000 and the 155 is right for about 3500 feet. If you are going to be running it at sea level you might even want to try a 160, and even a 162. You should also try dropping the clip on the needle one slot. The key is to experiment. Try one setting and then make a single change. That way you know what each change does. If you don't know the pilot and screw control the mixture at idle to about 1/4 throttle. The needle controls from 1/4 to 3/4. The main jet controld 3/4 to wide open. There are slight variations between identical bikes. What works for me might not work for you. You need to test.

If you are riding on the street the K&N is great. The consensus is that they don't filter quite as well as the traditional foam element for dirt riding. A little bit of the dust makes it through the K&N. Think of it as the price for the extra air flow.

Be sure to do some maintenance. Check the valve clearance and clean the oil screen at the bottom of the frame oil reservoir when you change the oil.

  • Kawabuggy

Posted February 28, 2007 - 07:39 AM


Thanks for the advise. Before I tear off down the trail, I plan on doing all of the required maintenance, to include the carb updates, the header grinding, the air box mods, the cam install, new piston, rings, wrist pin & retainer pins.

If the K & N allows dust in, I will replace the unit with a foam type.

In regards to checking jetting, this is what I have been told:

To check low to mid-range jetting, ride the bike under acceleration, then simultaneously press the kill button while pulling in the clutch. Stop the bike without releasing the clutch, pull the plug and check the color.

Likewise, I have heard the same about checking the jetting under full acceleration. Does that sound right?

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