Stupid Swede.


Would like to do these mods to my european NX650 that carries the 650L engine, but didn´t find the instructions above very easy to follow. :)

Do I have to drill holes in the carb in order to raise the needle?

What new jets and in which sizes are needed?

How does one get rid of and block off the "smogthing"?

What should be done to the airbox?

Thankfull for any hep! :D

No holes are needed. All you need do is unscrew the top of the carburetor to see how the needle and throttle cable work together. The needle has slots cut in it, and a C-ring (also called the "clip") that holds the position of the needle. Remove the needle, remove the C-ring, and replace the C-ring so that the needle will sit a bit higher when re-installed. Re-install the needle and close everything back up.

I am not sure of the jet sizes, but they are easy to replace. Turn the carburetor upside down, unscrew the large cap on the bottom, and you will see the main jet, which can be unscrewed and replaced. The pilot jet is nearby, but you will likely have to take the float bowl cover off to get at it.

I am giving you this from my XR650, which has a different carburetor (but not that different).

Good luck! PS the only stupid question is the one you didn't ask...

Hi guys!

And thanks for sharing that info.

What size jets did you use when performing these changes?

I have seen posts that says a 52 pilot and 1 155 main is fine when using the stock exhaust.

What do you think?

The airbox on my NX must be a bit different than the one on the XR 650 L. There is a "snorkle" on top of it which leaves a pretty large hole if removed. I took it off the other dat when adjusting the valves without having made any changes to the carburator and the bike ran like crap.

I just performed these mods to my friends 650L and I figured that the carbs would be pretty much the same on the L as they are on the R but, they are not the same all. The only things that they have in common are that they both are on Hondas and both deliver fuel and air.

1) You have to enlarge 2 existing holes to 15/32” on what they call the vacuum diaphragm.

2) The needle does not have multiple positions with a “C clip”. It is just dropped through a hole in the vacuum diaphragm and held in place by placing a small spring and retainer over it. To raise the needle, you have to slide a small washer onto it before you drop it back into the hole. This lets the needle sit higher on the top of the washer.

3) There is no large cap on the bottom of the carburetor; you have to remove the float bowl.

I also found out that I couldn’t easily work on the carb by just turning it 90 degrees like on my 650R. I had to remove both throttle cables and completely pull it out of the frame. However, I did not remove the choke cable.

I hope that this helps you. Feel free to ask me any questions. I would be glad to help.


Corona, CA

I forgot to tell you about the air box and smog pump.

Smog Block Off Kit:

It would be a little difficult to explain the smog pump removal so that you could understand it. Just purchase the kit from Baja Designs. Everything that you will need to know will be included.

Air Box:

When you remove the seat you will notice a couple of holes on top of the air box with two rivets holding the piece on. One rivet will be at the front of the two holes and the other at the rear. Use a 1/8” drill bit to drill out the center of the two rivets and pull the piece out. You are done!

Oops, sorry to mislead! Sounds like you have a constant-velocity type carb, typical of road bikes where constant jetting changes aren't needed.


just call Baja Designs. They will get you the correct jets for your carb.

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