Pilot Mixture Screws


PMS Location:

 

    Stock PMS screw cover location           Aftermarket PMS installed

 

 

  

                                                                    


PMS (Pilot Mixture Screw):


    Turning In (clockwise) = Leaner - you are turning the taper of the screw into the opening and allowing less fuel to pass


    Turning Out (counter-clockwise) = Richer - you are turning the taper of the screw away from the opening and allowing more fuel to pass.


The question was what direction does what when you turn the PMS screw? The short answer is outwards make it rich inwards makes it lean.
The PMS screws taper to a point. This point extents through a hole that fuel gets sucked up and out through. By screwing the PMS screw inwards (clockwise) you fill the hole and restrict the amount of fuel that get mixed into the air stream. By unscrewing the PMS screw (counter clockwise) you remove the restriction from the hole allowing more fuel into the air stream.
 The difference between the Stock PMS screw and the Old Style MaxMix screws are how fast they taper to a point. The old style MaxMix does it much faster, so if a stock PMS screws is 3 turns out the MaxMix is 1.5 turns out. New MaxMix screws have the same taper as stock, and should be adjusted that way.
 The start position for the stock PMS screws on a V Star is the number of turns specified in the jetting tables - out from lightly seated. Lightly seated is when you feel the rubber "O" ring on the PMS screw start to compress.
 
Suggested Pilot Mixture Screw Adjustment Procedures 

                Sync the carbs first.

                To adjust the PMS screws you need to drill out the brass caps that seal them, this requires removing the carbs. Drill a small hole in the cap and either wiggle the plug                 out with the drill bit or use a sheet metal screw to pull them out. If the carbs have been worked on previously, they will probably already have had the covers removed.

                Screw the PMS screws in until they are lightly seated...

                The next part is up to you.......

                A) if you think you can tune it by ear then run the screws out about 3 turns with stock screws, run the bike and see if you have popping on deceleration, if you do then                 turn them out in 1/8 increments until the popping goes away and you will be close enough. Re-sync the carbs after doing this.

                B) PREFERRED METHOD - The Lean Drop -  If you have a tach, start at 2-1/2 to 3 turns out equally on both carbs with stock screws and then gradually turn each                         screw in until the idle drops slightly. Then back them out slowly to the point the idle just comes back up. This is called a "lean drop".




Stock / MaxMix Thumbscrews  

 

For Carb Tuning - One Stock PMS Turn EQUALS 1/2 OLD Style MaxMix or Metric Magic Turn (2 to 1 ratio) 


New MixMax is the same as Stock

 

When you rejet the carbs you will need to drill out the cover over the PMS screws, which are inset into the bottom of each carb. Once done rejetting, you can (but not easily) do your final tuning with the "buried" PMS screws, or you can replace them with  MaxMix or Metric Magic PMS screws. They protrude out of the bottom of the carbs, making it much easier to adjust with your finger -- or, better yet, a 1.5 to 2.0 inch long piece of rubber hose - with the right ID to fit over the thumb screw head of the screws.  In my case, big fingers and hands made the "rubber hose" trick a necessity.

 

Some people don't like the MaxMix screws, because they have a faster/sharper taper than the stock screws, and therefore are not as fine for adjusting.  However, most who have them swear by them - and personally I have had no problem. Note: Max Air is now shipping a new style that has the same taper / profile as stock - much finer to tune with, plus long stem for tuning.

 

  Stock and Old Style MaxMix PMS screws

 


Stick with Stock PMS Screws?

If you decide to use the stock screws, the right tool will make it easy to do the adjustments  Courtesy of the ever helpful Daddo, here's a link to the offset Pilot Screw Adjusting tool   http://pitposse.stores.yahoo.net/popiscadto.html

 

          

Another tool (Thanks to Vstar_in_NH)   Finger Bit Set from Sears

 

And Another Solution - rosskp:  Here is a picture of a screw that I soldered using an old pilot jet, can be done with JB weld, an Metal Epoxy. Make sure you don't get any on the threads.  (Note: rosskp uses a fuel line hose to grip the add-on to the screw - making it easier to grasp and twist in the confined space.)

 

      

 

And another: mitchyd - drilled and taped the PMS screw ran a nut up the small screw/ bolt against the head with a star washer for grip JB weld into place so doesn't vibrate apart:

And another: Tundrawolf: I used a 1" Copper Rivet (Hardware store 25c a piece), Oatey Water Soluble tinning flux (for joining dissimilar metals) (Lowes Under $3 I think), a cutoff disc on my Dremel to shape the end of the Rivet -- The final result was a small slit that fit snugly into the notch of the mix screw.  Maing sure of the best alignment BEFORE trying to solder the two pieces, it is best to hold the tip of your high wattage soldering gun mostly to the rivet, and partially to the PMS screw, if the rivet is on the bottom-as heat rises.

 

imnezrider (mdpar3) - Socket/driver bit...beats the heck out of pullin' carbs.

 

           

 

Metric Magic's PMS Needles, with Finger Turn Heads: This is a great choice to fast and simple PMS adjustment. Keep in mind that 1 turn on Tim's Screws = 2 turns on the stock screws.



Mikuni Pilot Thumbscrews:             

 

These Mikuni parts will fit the 1100 carbs and allow the pilot to be adjusted without the use of tools... look for these Mikuni parts.  NOTE: Set them accordingly (they are NOT the same as stock PMS screws!) Turn them out half as much as the stock screws.


  (2) O-Ring, Fuel Screw N133.037
  (2) Washer, Fuel Screw VM12/33
  (2) Spring, Fuel Screw N133.206

  (2) Screw, Pilot Fuel 604-26003   




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