Pumper adjustment TM40 Xr600

7 replies to this topic
  • Laggie

Posted August 14, 2005 - 02:01 AM


First, sorry for the english (swede). This technical words are just not easy..

How is your pumper adjusted for your Mikuni Tm40?

I can´t get the bog to dissapear :D

Right now i have 20 pilot, 142,5 main, needle att the forth position (more fuel than middle).

I took the carb out to watch the pumper in action (courios), I thought the fuel would "squirt" more, now it´s just like a waterhose right out the carb. Is it just the intake-air who mix the fuel? Just thougt it would be a fuel"mist" the pumper sprayed inside the cylinder..

Thanks for the answers.. / Lars

  • BWB63

Posted August 14, 2005 - 08:31 AM


What is your air jet at? It is a small jet in the back of the carburetor where the air comes in. It's at the bottom. Try a 1.2

Then go with a 22.5 pilot.

What is the Needle jet and needle

  • Laggie

Posted August 15, 2005 - 06:14 AM


Ok, i´ll check the airjet and what needle I have.

But whats the needle jet? Isn´t that the main jet?

  • BWB63

Posted August 15, 2005 - 11:22 AM


Ok, i´ll check the airjet and what needle I have.

But whats the needle jet? Isn´t that the main jet?

The needle jet is the jet that the main jet screws into. It screws right out and has the number on it's side. The needle depends on this jet to work. It all has to do with the vacuum and how much how fast your engine makes. The TM40 was made for the Harley and lots of the TM40's still have the basic jetting for that with just the pilot and the main changed. Mine came with a Y-6 needle jet and most come with a Y-8 but, I had to run a Y-4 needle jet with a 90JY1 needle. To get the bog out. I could then run the pump much later. The air jet feeds air to the pilot and needle jet and is .9 on most and is way to small. The Harley is a V-Twin and can pull more air so, our single needs a 1.2 air jet or bigger. The air jet is real small and the number on the side of it is real hard to read.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Laggie

Posted August 16, 2005 - 12:21 AM


:D I bow for your wisdom and willingness to share :D

Now I have something to do today, i´ll check so that I can order some different sizes.

  • Laggie

Posted August 18, 2005 - 02:45 AM


Ok, now I´ve checked.

Pilot jet: 20
Main jet: 142,5
Air jet: 1,1
Needle jet: Y6
Needle: 9DJY4-96
Needle position: 2nd from the bottom (more fuel than middle)

So your saying I should change the airjet to 1.2, the needle to Y1, needle jet to Y4 and the pilot jet to 22,5??

My bike has the air(snorkel?) removed, high compression piston and fully opened slipon.

Thanks for the help!

  • BWB63

Posted August 18, 2005 - 11:37 AM


We have different bikes and the flow of each will be different but, what I had might get you closer. I would get a 1.2 air jet and a 17.5, 22.5, 25 and maybe even a 27.5 pilot to have to test. I had the same needle and needle jet as you have and it is what is used for the Harley. I went Y-4 and changed the needle to 90JY1 (You have the older needle like I had) I got all my jets at the Harley shop. I thenk you should have a 135, 137.5 and 140 main. It's a start. I would change the air jet and pilot first and see how much that helps on the bottom end the go to a 135 or 137.5 to see if that is the right direction. then if the middle throttle is not right change them.

  • Laggie

Posted August 19, 2005 - 12:51 AM


OK, have to order the jets so it just takes some time.. hard to live in the woods:-)

Related Content


Post Apocalypse, ThumperTalk style! by Justin Pearson

Dirt Bike   General Dirt Bike Forums   General Dirt Bike Discussion
  • Hot  35 replies

Supercross Preview 2017 Part 1: Championship Contenders by Chris Cooksey

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  186 replies

Cle Elum Sunday 5/29: Looking for dual sport tips by TigerTanker

Dirt Bike   Dirt Bike Regional Discussion   Northwest
  • Hot  32 replies

Wiseco 101MM Spark Knock Low Engine Temps by imandrewparks

Dirt Bike   Make / Model Specific   Honda   XR600/650
  • 9 replies

DirttyPig 2005 Xr650l Prroject! by braapmebb1moretime

Dirt Bike   Make / Model Specific   Honda   XR600/650
  • 22 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.