Final questions about XR650L carb mods

I have read the article about 650L carb mods by Dave and Brian. I understand why to drill out the slide, and why to raise the needle. But my question is about jetting and the air mixture screw. I have a full white brothers E-Series exhaust and a K&N filter. When I go to re-jet does a 160 main and a 55s pilot sound right?. Also what do you look for with the air screw? Do you check the spark plug? Is it in the performance of the bike? Or maybe the idle? And can you damage the engine if it is a little off? And finally how do you test all these? Can someone with experience with these modifications please give me some advice. It would be greatly appreciated.

160 is prob. a good place to start, maybe someone here who's running that pipe will chip in. I'm guessing you'll need to go a little bigger on the pilot, but I'm not sure.

The way I could tell the pilot jetting was a little off was when I'd romp on it for a good distance and then stop and let it idle- if its a little too lean, it'll stall, or almost stall. If you go more than 2.5 turns out on the idle screw, you need a bigger pilot jet.

As far as I can tell, the only way to get the jetting perfect is to find what's a little too rich, then go the next size smaller.

Dave aka Dave_CL

They make a Edelbrock for your bike............... :naughty:

I agree with Dave, he's the man. I have the e-series s-bend and run a 58 pilot and 160 main, its perfect at about 2000'. Also I believe the screw is a fuel screw not an air screw, meaning that if you turn it out you'll be richening the mixture, if its an air screw you'd be adding more air leaning out the mixture when you turn it out. Anyway mine is between 2 to 2 1/4 turns out depending on the air temp.( I live in North Dakota and ride between 20-100 degrees.) I run 12 discs in my exhaust and if I start to backfire on deceleration then I open up the screw about 1/8 turn, it does make a difference. I recommend you take the smog stuff off as many posts here can tell you how and the block off kits to do it with. If your fuel screw is set right your bike will not backfire under deceleration and like Dave says your idle will be rock steady after a hard romp or extended idle at stop lights etc. A side note if you use the smog block off kit, do not disconnect the anti-backfire valve selanoid, it should have a hose connected to it and not blocked off. There's lots of threads devoted to telling you how to do that as well. I hope this helps and lots of luck.

Thanks for the info, I'll try the jets you have. Also what thickness of a needle washer did you use? The article said between .020 and .030.

yep, about 20 or 30 thousandths.


I just got my jets in the mail yesterday, and am gonna mod my carb this weekend. Going to use 158/58 combo for San Diego area (0-1500ft). I have a Uni ready to go and will remove the snorkel of course. I am running the WB E-Series S-Bend also, and love it so far. Even the tiny spot on my fender that melted away dont bug

I hope all goes well, as I will also be adding a Summers Racing fork brace, Seal Savers to remove the accordian boots (yuck!) and adding the top fork cover guards over the seal savers as well. Should be fun removing the carb and, then putting it all back together to go play in the hills.

I went ahead and did the carb mods. The throttle response is allot better. I am at 1500 feet. The only problem is that the bike doesn't want to idle right. After throttling it, the bike goes down to a idle and gradually slows till it dies. There is a little smoke now, could it be that the jets are to rich, or maybe just one of them? Or is the pilot jet to lean, should I go to a 60? I put in a 160 and a 58. I had the mixture screw set between 2 and 3 turns with no real difference at idle. What are the characteristics of a too - rich situation. Before I started I had a 152 and 50 pilot. Anyone have any ideas?

I got a bug up my ass, and a head start on my weekend mods. It took me about 3 hours including a trip to Radio Shack for the washer assortment to get the right size.

Installed jets, ground tab off bottom bowl (so you can turn screw easier by hand)...and installed my Uni filter. Did a very small test drive (time for work :naughty: ) And it seems pretty close. May need to adjust mixture screw upon more testing, but it felt great.

Thanks to all TT members who have advised and assisted, Especially big DAVE !

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