I have my son’s Honda XR650L on my stand and I am trying to help him get it running properly. It stumbles and pops thru the carb as you will hear in this video. Do you guys think this is a carb issue or is it an ignition issue? It only happens a few times in this video and it is much more noticeable standing next to the bike……

*are the valves in good shape and proper clearance?
*It almost sounds like lean fuel on throttle up.
*plug health
*verify air screw setting.

Sounds like fuel to me. My 40 flatside loves to gum up after sitting a few months.

Thanks for the suggestions. The plug is new and I’ve tightened up the huge gap it had from 32 to 20. I’ll probably adjust the valves….
The previous owner removed the smog box and plugged the lines but he didn’t upsize the jets as needed when you remove the box. So I upsized from 50 to 55 and from 152 to 158 as noted everywhere online. I also shimmed the needle which was also recommended. I disassembled and cleaned the carb in my ultrasonic cleaner. We replaced the slide and its diaphragm. ($125) I will change the K&N air cleaner back to the original foam style. There is a second diaphragm on the side of the carb which I have not yet changed. It supposedly eliminates the decel popping thru the exhaust, but other than that it isn’t typically an issue. I’m not a fan of this style carburetor. 

When my boys were young we rode nothing but Honda XRs. Which is why he bought this bike. They rode thru the XR100, XR200, XR250, and XR600. All of which ran flawlessly and never needed my attention. The XR200 is an excellent bike for riding tight single track thru the trees of northern Michigan. And they were like farm tractors. Keep’m well oiled and they run forever. Then along comes this one…..

sounds like you did everything right. does that carb fire raw fuel as enrichment like some of the flat sides?

btw, here is an old friend from 2003. still have the yellow one.

No, This is a Keihin CV carburetor and it does not fire fuel into the engine as an enrichment mechanism.

And I would have preferred the 400 like your old friend in the photo but our XR days were prior to the 400 model.

imgur.com/a/xobJSfx
 

Well I replaced the small diaphragm on the side of the carb which supposedly eliminates the popping during deceleration but it did not eliminate the issue I have at idle.

I have not adjusted the valve clearances because I just don’t want to open a new can of worms and I really doubt that it would cause this popping at idle. Besides that I’ve never adjusted valve clearance although I’m sure I’m capable of it. Just need to find instructions on how to do it.

This appears to be a common issue with this exact model bike. A google search yields multiple hits on the popping issue. I’ve already done what they suggest. I hate to bring his bike back saying I couldn’t figure it out……. So I’m open to more suggestions.


 

Lovely bike. XR is a really easy bike to do valves on and one of the reasons I love these types of Hondas. Pop the tank and unscrew the valve cover plugs (I'm guessing the 600 is the same as the 250) it's that easy. You just have to be sure you are on the compression stroke at "T" and not the exhaust stroke

I wonder if it's the filter?

Do you find these bikes run really HOT. Mine is blisteringly hot even just doodling around on a cool spring evening, hottest engine I have ever known but just a blast to stick in 3rd gear and ride everywhere. Maybe just take it for a ride and the problem will sort itself

obviously a lot easier to give advice from a computer desk (  and eat donuts, drink coffee, etc...) than fix it, but engine sounds lean on throttle up.  

If its a 93, found a manual online.  You probably have one already. 
biker.ee/manuals/Honda/Honda_XR650L_Service_Manual.pdf

The manual has a lot of good ideas under troubleshooting, section 19, even its its not a 93.      

* air leaks ; spray intake w/carb cleaner
* restricted fuel flow
* clogged muffler
* pinched tank breather
* ignition timing ; test warm 1,300 and 4,000rpm using timing light.
* valve lash; verify lash only. ok..that was my idea not the manual

Good luck sir... I am busy and have to finish my coffee and solve other problems on the internet....one of which is a hole in my fuel tank.

Great info as usual Pabdt!  

Thanks for the suggestions and the link Pabdt. It had one exhaust valve that was about two decimal places out of spec! I have no idea how that occurred because the locknut was very tight. I’m talking it had about 3/16” of slop. I also made a minor adjustment to the other valves now being .004” to .005”.

It is now 99 percent better. It still seems to have a minor miss but it ran good when I rode it back to his house. I told him to run the thing for a while and let me know what he thinks.

This first video shows my initial inspection at TDC compression by simply using pliers to see how much play there was in the rocker arms. Hence my surprise on the last valve.



This next video shows a decent improvement although I don’t think it is quite right yet. he is going to report back to me after putting some miles on it.