Well, I have had a few rides with this little puppy, and while the bottom end is great, the mid-range and top-end can only be called boggy.

My DS is running a Custom X series 2 pipe, with a K & N SN-2550 & outerwears off the carb. I am riding about 40' to 50' above sea level, the temperature here is usally around 65 - 100 Farenheit.

The settings of the carb currently are:
Needle: top postion
Main jet: 140
Accelerator pump: 50
Primary: 25
Needle Seat Valve: 4.2

I have had it in the shop 3 times, and I get the feeling that they are just incompetant, I am fed up donating to their little charity.

Has anyone got any ideas on how to get this running right? I am just about ready to relocate this carb to where the sun don't shine.

 

Where did you get the HSR42, Ron Woods, or did you buy it and set it up yourself?

I have a polished HSR42 in the garage (recently re-designed version). It ships with a #97 jet needle. Is this the jet needle you are running? When you say needle top position, do you mean the needle clip in the lowest or highest position?

The settings that worked best for me were:

#97 jet needle, needle raised all the way (richest setting) (clip in bottom position)
#30 pilot jet
Pilot air screw 1 1/2 to 2 turns out
#160 main jet
#60 or smaller accelerator pump nozzle.
Accelerator pump stroke set to near ZERO.


WITH THIS COMBINATION OF JETS:

Anything smaller than a #30 pilot jet was too lean at startup, idle, and just off idle (popping).

Anything larger than a #35 pilot jet showed a loss of low end power/response off idle.

Running the pump usually seemed to be too rich and boggy in the midrange. Never did find the right setting for the pump, but it ran pretty good without it.

There are different jet needles available, but the only difference is the diameter of the straight portion of the jet needle, so this will "only" tune idle up to 1/4 throttle.

This setup gained ~ 0.75 second in a drag race to 70mph. I have experienced some minor bogging with the carb, but it is difficult to get jetted perfectly without a dyno and custom carb parts. Also, the stock CV carb lets the motor rev as fast as it wants to, but no faster, so you won't feel any bogging in the mid and upper range. The flatside carb "forces" the motor to rev whether it wants to or not. Also, the higher the flowing the exhaust the more likely I was to experience bog. The carb seemed to be much less picky with a near stock exhaust.

There are manuals available in PDF format at www.mikuni.com

 

Thanks for the info Scooby. What exhaust and elevation were you at with this carb?

Bought the carb and had it installed by a bike shop who promote themselves as being experts in four stroke bike motors.

They had three goes at getting the jetting right and each time they touched it it was worse than the time before. The needle is as far down as it can go.

I am trying to get the jetting right, between myself and a mate who is a lot more cluey on motors than I am.

I am fed up with paying money for no apparent gain to these turkeys.

Once I get the carb running right, all I need to do is work out a way to get the thumb throttle usable, as it is very stiff. You get a good thumb pump after about fifteen minutes hard riding.

 

Ozzy,

Ron Woods sells a lighter (pull) spring for the Mikuni T42/45, it costs $14.00 and it made a big difference on my Mikuni TM45. They send the instructions which were very easy to understand and follow.

 

around 500 feet elevation, big gun exhaust

 

Sandsurfer, thanks for the info about the spring, have ordered one from Woods, Should fix the thumb pump nicely.

Scooby thanks for the info, downloaded the tuning guide from the Mikuni website, it's a pretty good document at first read. Have ordered a few more jets, and will try and get it running right this weekend. I will cut down the stroke of the accelerator pump.

 

The carb is now runnin the best it ever has, changed a few parts, and had a few drags with Peter. The bottom end is still pretty good (if only it translated to acceleration and not wheelspin), the mid-range of the motor now is awesome. From a rolling start in 3rd, I opening cans of Whoop-A$$ all over Peter. From a standing start, even in second I could not get the lead.

Have changed the settings as follows

Pilot Jet: 15
Needle Seat Valve: 3.5 (4.2 is stnadard)
Needle: 98 (slightly leaner than the standard 97) in top clip position
Main Jet: 140 (will try a 160 next weekend)
Accelerator pump: 50, but pretty much not being used.

The only area which is slightly boggy is from approximately 1/2 to 3/4 throttle, will try different needle positions next week. This is easily fixed - just floor the throttle, and it gets rid of any hesitation.

This is definately way quicker than the stock carb now. Just waiting on the postman to deliver the lighter carb spring.

 

Ozzy,

Did the lighter spring help? I installed mine on my 45MM Mikuni, removed the accelerator pump linkage and spring bumped the Pilot to a 35, needle on the 3rd slot and running a 165 Main Jet. Great response through out[img]i/expressions/face-icon-small-smile.gif[/img][img]i/expressions/face-icon-small-smile.gif[/img]

 

OzzyDS, The weaker spring can't be used with the accelerator pump rod in place. I used a thumb saver (modified).

I'm concerned that your jetting is too lean. I have tried the 98 jet needle in the position you mention, with small pilot jets. I used a heated 4 wire oxygen sensor with an air/fuel meter. Way to lean, for maximum power. Also, be careful with the main jet, it is too small from my experience.

I have spent many many days tuning the woods 45mm carb and the 42mm version.

Check your plugs.

The midrange power will go way up when you raise the jet needle.

 

Scooby, will order the jets you recommend and install them, and try them next weekend. I definately don't want any damage to my engine.

I don't mind removing the accelerator pump rod - its not like I am using it. I definately will stick with the thumb throttle.

I hope you have your beast running well!