TMX 38 - Mikuni tips
by
Pilar Rivera III (son/enthusiast)
I understand the frustration that the Mikuni 38 carburetor can cause. Having owned a couple myself, I've gained some valuable insights that I’m eager to share. With our new big bikes now featuring the TMX 38, I hope to provide helpful information to make your experience smoother. The TMX don't have to be a frustration at all in fact, it can be an advantage when set-up and tuned correctly. Let's navigate these challenges together!
TMX 38 exploded view / parts
I like to keep parts on hand for the carburetor. There are a couple gaskets/ o-rings that are a must have if you want to be ready for anything. I added the parts list for your convenience. We will refer to the parts from this list when explaining a couple of the special attention areas.
TMX frustrations
I've experienced frustration with the TMX38 soon after acquiring the bike due to the dreaded gas leaking from the overflow. These carburetors are well-known for that issue, and tuning them can be a little tricky, particularly with the newer big models. While many choose to replace the carburetor with a different brand as did I. I was determined not to let it defeat me—I’ve seen these perform really well in the past! After tackling the problems a few times, I discovered some helpful tricks that really made a difference. I'm sticking with the Mikuni because it performs better on my 125 than the others including the Keihin!
Trust Me - I know!
If you're feeling frustrated, know that you're not alone; many of us have been in your shoes. Together, we can work through the challenges you face. It's surprising how many impostor Mikuni parts are out there, especially when it comes to jetting and needles. Let's tackle this issue and find the right solutions for your setup!
Most Common Frustration
It’s common for Mikuni carbs to leak through the overflow, and many owners spend hours adjusting the float height without realizing the root cause is often the float valve or the hidden o-ring in the valve seat. The original o-ring is typically low quality and can fail prematurely, leading many to consider alternative carburetors. Fortunately, a better solution is available through a kit from JD Jetting, or you can source your own fuel-rated o-ring. While changing these o-rings can be tricky, with a few tricks of the trade, you can resolve the issue and enjoy hours of worry-free riding.
The ole Jet Block
The old Jet block gasket is constructed from a weaker material and is prone to failure. The stock gasket frequently fails at the port because the soft rubber deforms, leading to a loss of seal. After only 10 hours of use, the deformation of my old gasket is evident. Thankfully, the same kit I use for the float/needle valve seat comes with an upgraded gasket that is made of much higher quality and reinforced material. SEE BELOW
Kits for the right fix
Give your ride a new life with the JD Jetting kit! This long-lasting solution is designed to revitalized your Mikuni's performance, unlocking its full potential. After you fineune it, you'll experience a ride that outperforms the competition Dial in that Mikuni and get to dominate the trails with an exciting BRAAAAAAP!!!