NEED HELP: XR650L Pilot Screw Problem


It was inevitable. I had to adjust the pilot screw 1/2 turn after installing a Uni-filter on my 98 L. What I didn't expect was it falling out after test riding it! :D

I found the screw, put it back in, but needless to say I'm pretty unsure how to get this d-mn thing to run right again. How sensitive is this adjustment? Do I need take it to a mechanic? :)

I've got it to idle o.k., but it pops and dies (more than before adjustment) when downshifting and coming to a stop. I kind of remember the position of the pilot screw before it fell out, but I didn't seat the screw and count how many turns that was.

Any advice, other than going to the dealer, on how to remedy this situation is greatly appreciated.

Did you find the spring also?Start with two turns out form lightly seated, and adjust from there.DirtRider magazine has a good article on four-stroke jetting(nov 03).Are you running the stock pilot jet?Stock is a 50,with just an air-filter mod. go 52,with pipe go 55.Hope that helps. :)

Thanks MotoChris,

I do have the spring and the Honda Shop Manual.

I tried the initial setup and settings per the Manual. No go. Way to lean. The carb has a #52 slow jet and a #155 main jet. Before I did any turns to the pilot, I could see the exposed threads of the pilot screw below the opening. That's why I put it back roughly in the same place.

My thinking is since the screw doesn't have the factory keeper on the head, it might have been slowly backing out due to vibration when riding all this time. This meant it wasn't properly adjusted for quite some time or at all. The bike did run better with the stock air filter like this, go figure. I don't want to go back to that.

What I do know is that setting the pilot screw per the manual and opening the throttle it hesitates (it still does, but not as bad as with the factory settings).

Still not 100% and it needs more fine tuning, maybe more carb mods if the screw needs to backed out so much? :)

I've used as rich as a 60 in mine, near sea level. That being said, don't expect to solve all of that carb's issues with a pilot jet. Drilling out the holes in the slide helps (see other posts for details). Many XR650Ls will always have a bog under certain conditions (low rpm, quick snap of the throttle), something you learn to live with unless you want to buy a pumper carb.

That's probably true, but upsizing the pilot screw is a good place to start as stated in the other posts. I at least want to make sure that enough threads are engaged to keep the (properly-sized) darn thing in place!

I've heard about "drilling holes in the slide" but really don't exactly what that means. Any recommendations, or is any on-line information available about how to do it? :)

Improving throttle response on a CV carb can easily be done by trimming the slide spring and drilling out the vacuum hole on the underside of the slide. I have done these mods on CV carbs on a KLX300 and KLR250 and throttle response is greatly improved. The bikes jolt forward when you wack the throttle. Not sure if this would be desirable on a big 650 though! As usual, proper jetting has to go along with the mods. There are various makes and sizes of CV carbs, but the concept is the same - you want that slide to move up fast! Here are two links:


Thanks to you and to everyone for the tips and links. I'll post a message to the group after I change out the pilot screw for a larger #55 and let you know the results.

I'm also going to adjust the number of disks on my Trapp up or down to see if that'll help. Right now I'm running 8 on my IDS Quiet Core.

Thanks again and I'll keep you guys posted.

Time for an update regarding the various issues I've experienced lately with my 98 L. :)

Rear suspension click: I cranked down on the upper adjusting nuts and compressed the shorter aftermarket shock spring and seated the spring better and the "click" is gone! This is the same procedure as decreasing the sag for the larger stock spring. I only wish I had the proper spanner wrenches instead of the hammer, punches and screw drivers I used. Only minor damage was inflicted. :D

Pilot screw: I extracted the carb (never done that before) and replaced the #52 pilot "jet" with a #55 (never done this before, either) I picked up from Baja Designs for 2 bucks. I reassembled the carb, reinstalled it along with all the other hoses, cables, and connectors. After some test riding and tweaking, I probably could use a #57 or #58 since I had to back the pilot "screw" out to 4 turns. But let me tell you, this bike runs so SWEET NOW! :D

No hesitation, popping or bogging. Just smooth performance throughout thegears, rpms and powerbands. I learned a hell-uv-alot tonight. I wasn't sure if I was going to attempt any of this, but I am sure glad I did.

Thanks for the tips and advice. :D

Holy cow! 4 turns, yeah that seems excessive. Can yu give us an idea of what your current setup is now. I.E. number of discs, main jet, pilot, air filter, box mod, etc.?

I am running a FMF Q, 55 pilot, 165 main, snorkel gone, K&N airfilter, slide drilled, and Dynojet needle. Mine rips from the bottom to the top with no hesitation or bog and no decel pop. It's hard for me to think your could be so much different. I suppose the most important thing is what elevation and temperature are you at? :)

Thanks for the reply uw153.

(1) 1998 XR650L bought used with 1.9K miles, most of the mods already in place, never on dirt and never had a first service other than an oil change. I've had the valves adjusted and I've put about 600 miles on it, mostly street, but one great dirt ride at the (now torched) Corral Canyon ORV Park.

Right now my set up is a 155 Main Jet, 55 Pilot Jet, Supertrapp IDS Quiet Core w/8 disks, Uni-air filter and the snorkel's ejected. I'm down at sea level and the average temp is 72 degrees F. For what it's worth, I run 89 Octane for ignition and lift-off with no problems.

I think a larger pilot jet is needed, but I really don't want to repeat this process again anytime soon.

This bike must run extremely lean. I'm not a mechanic so I don't have the answer(s). If I do any other carbs mods it'll be swapping out the stock dual-stage model for a gas-guzzling, single barrel pumper carb. :D

Right now I'm good to go with 4 turns out on the Pilot Screw since installing the Uni-air a week ago. It's definitely MUCH better than it was. It was so far out of whack before that it fell out on me doing the slightest adjustment. It won't do that anymore!

Let's see...what's next on the list: Pirelli MT 21's, Clarke 4.0 tank, new alloy bars... :)

Your main jet is probalby too small(stock is 150).With a pipe i would go 162-165 or larger.Do you have the stock needle(needs to be shimmed or aftermarket adjustable).Four turns out on the mixture screw is too far out,but your pilot jet size sounds right. :)

Hey MotoChris,

Haven't done the "needle jet" mods yet. Really don't know what that is or how to do it. Haven't drilled the slide either. I thought about these when I had the carb out since it's not an easy task to remove it in the first place, and I don't want to make it a recurring event.

What exactly will happen with the pilot screw "too far out?" I rode it for 600 miles with the stock air filter and this dang screw "way too far out" before I installed the Uni-filter and then the pilot jet. It now runs better than it ever did before. Is this only a temporary condition? :)

From what I've read this adjustment is only for idle up to 1/4 throttle. After that it isn't supposed to be a factor.

Any specifics are appreciated.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now