650L carb opinions needed

What do you guys think about this?

Thanks to ***** information and knowledge on the 650L carb we have come across what I think could be a jetting problem solver for many 650L riders who have done the carb mods by Dave and Brian. The 650L carb seems to operate a little differently than I had previously thought. At 1/4 throttle and under- most of the fuel is supplied through the bypass ports which is controlled by the pilot circuit or jet. Also the throttle plate in the carb needs to be closed enough to block the bypass ports off and let the motor idle only off the idle mixture screw. What I am getting at is the stock 650L is lean on the pilot jet for emission purposes and the idle is raised and mixture screw is richer, allowing more fuel for idle. By going a little richer on the slow jet(example a 55 to a 58), leaner on the mixture screw(1 turn out on pilot screw), even maybe a little leaner on the main(example - 160 to 158), and lowering the idle you seem to gain the following:

1. Better idling under any and all circumstances

2. Lower operating temperatures

3. More low and mid range power

4. Still even better throttle response

5. A lower but more stable idle

5. A spark plug that always seems to be tan and gray(which is perfect)

All info on the operation of carb was pulled out of the service manual. I have been looking for a reason why my bike's spark plug colors seemed to change depending on what kind of riding I was doing. This changed the condition for the best and so far it runs better than ever.

My carb is setup as follows - 158 main, 58 pilot and mixture screw is about 1 turn out, depending on elevation. Also I lower the idle way down to close the throttle plate fully to let the bike idle off the mixture screw only.

Drilling the slide is mandatory for good throttle response.

The dynojet needle is poorly shaped- it has a large step in it, and radical mixture changes are not conducive to smooth throttle response.

The stock needle is fine, it just lacks adjustment- hence the shimming to raise it a little.

55-158 is the standard recipe, some have been tweaking it with good results.

I think the 58-158 is for a setup with an aftermarket pipe.


A friend and I recently completed the Dave and Brian carb mods with excellent results. We both recently purchased new 05 XRL's. We are near sea level in Houston, Texas where it gets very hot. The following was our recipe:

55 Pilot

165 Main

Stock needle shimmed.026"

Slide holes enlarged to 5/32."

2.25 turns out on the mixtue screw.

Big Gun, EVO "Quiet Series" complete system.

K&N high flow filter.

Snorkle removed.

We get an instant start, smooth idle, and excellent throttle response throughout the range and checking the plug indicates a good mixture. So far we are very happy with the mods. Thanks Brian and Dave!


Yer welcome, Mac!


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