Mikuni TMX

[croat1]

I figured I’d post these comments here in a new thread (info was talked about in another thread).  I’m curious...who runs a Mikuni carb?

Your switching from a Mikuni to a Keihin? Is it a TMX from an 01 CR250?

[croat1]

Michaels response:

Yes.  I’ve had the Mikuni TMX for many years and it has never really felt spot on

[croat1]

Kevin’s response:

Did you swap out the factory S-9 needle jet for an S-8?

Not the needle that goes in the slide, the needle jet is the removable emulsion tube that the main jet threads into. The TMX from the 01 CR had an overly rich S-9 needle jet which made them fat in the midrange & made them feel sluggish transitioning from the idle circuit to the main jet. I swapped the S-9 needle jet out to an S-8 on my buddy's 01 CR & put in a 400 main & it woke that bike right up. It was a different animal after that simple jetting change. Those needle jets are $22 from jets-r-us. The Mikuni TMX has gotten a bad rap over the years but there really hard to beat when set up properly. They have more tunability built into them as well.

[croat1]

Michael’s response:

What you described is exactly what it does.  Eddie told me to adjust The pilot and needle leaner to make it responsive.   I think the midrange was way to lean.  But if I richen it, it Is boggy down low.  It was running like shit trying to do tree shots.   So boggy it would almost die.  Good Info to know.  My tmx has the adapter ring from ESR.  Fits like a glove but I’m switching to a standard bell for a custom no link intake.

[croat1]

Lastly Mr. Halls response

I also prefer the Mikuni carbs because they have more circuits to adjust.  The PE, PJ, PWK, Air Striker do not have the ability to change the Air Correction Jet, Needle Jet, or the size of the Float Valve Seat. 

Needle jets ware out in all carbs.  This is the main reason that needle selection varies among those that have the same engine package as others, but need to have a different needle to compensate for the ware in the needle jet and needles.  Another reason that Keihin needle jets ware out so quickly, is they are using a bronze needle and a brass needle jet.  Common engineering practice is not design mechanisms using similar base metals for components that have two surfaces that slide over one another.

Mikuni uses a brass needle jet and a hard anodized aluminum needle.  Using dissimilar metals greatly reduces the ware on these two components.  I cannot remember when I measured an old Mikuni needle and found any ware when compared to a new needle.  When I measure a Mikuni needle jet and find ware, I just replace the needle jet and not have to spend $200.00 worth of time searching/tuning for a new Keihin needle that will restore the performance to what it used to be when the carb was new. 

I have to use a small bore gage to measure needle jets.  You cannot use gage pins to check the ware in needle jets, because the needle jets holes become oval in shape.

[croat1]

I have a Mikuni for the first time ever on a new engine.  Anxiously waiting for spring to put it through its passes.

Joe

[2ndmoto]

I have one. I pulled it off my CR and put on and AS. I couldn't make it work. There is lots of love for them, but I wanted to ride not fuss with jetting. I am sure it would be awesome once set. I might look at it again

[The norm]

The TMX has the potential to be a great carburetor, but I do not have the time nor interest to figure out how to tune one without burning up an engine.  Hell, I barely have time to keep my fleet of R's going and tuning the pwk's we run.
Loren

[desertR]

I wonder what it would take to adapt a fuel injection system. Carb's are so crude and old school, simple to do, but one of the most talked about things here, and what seems to elude many members/people here. Fuel injection has been around for more than 40+ years,so there's no magic here. I haven't ridden an off=road injected bike/quad, but my street bike is Injected, and it is Much better then carb's, and it's Italian. Most all street stuff is injected, so there's plenty of parts/systems available.
desertR

[Hawaiiysr]

2 stroke direct injection is a thing. KTM was in the works for a street legal 2T bike. Yamaha makes a direct injection outboard engine. I think the bottom line is, a carb is cheap

[desertR]

I  think that is the next logical step. There are also currently a couple of 2-stroke's that are injected, Manufacturers have done many changes to their motors when they went to injection. (more power/torque ?)  My current DD is direct  injected, and it"s great.
desertR

[desertR]

Fuel injection pressure is a concern, My car idles at 450/500 psi and WOT is over 2400 psi
desertR

[2ndmoto]

I have seen a few write ups on fuel injection conversions for banshees.

[Skeans1]

Fuel injection pressure is a concern, My car idles at 450/500 psi and WOT is over 2400 psi
desertR

Different application but my latest falling saw is a fuel injection saw it’s a low pressure system that you prime when cold after that it’s just a single pull to start.

[desertR]

Fuel injection pressure is a concern, My car idles at 450/500 psi and WOT is over 2400 psi
desertR

Different application but my latest falling saw is a fuel injection saw it’s a low pressure system that you prime when cold after that it’s just a single pull to start.

On my DD you MUST do a high pressure pump fuel mod before you add any power. Every internal part is replaced,$600.00 to 1000.00. The high pressure pump is motor driven, pump in the tank puts out 68 psi that feeds the high pressure pump. With my motor if fuel pressure drops below 1800 psi at speed, it will go lean and melt a piston.
desertR