Originally Posted by mrholmquist

I am not here to argue with you , in fact if you can teach me something I don't know by all means please do, no one is above learning something new.

As for the adjustment procedure you suggest using the pilot air screw I think you will find it does not work. Because the pilot air screw controls an air bleed passage which leads to the pilot air jet it never will stop the flow of fuel through the pilot fuel system regardless of position. It will not react in the same way an idle mixture screw will on other carbs. In the case of a carburetor equipped with an idle mixture screw screw there is no pilot jet.The idle circuit fuel flow is controlled and can be directly adjusted or even stopped by turning the mixture screw. You will not get near as drastic results turning the pilot air screw on a mikuni carb. It will not cause the engine to in your words " act like it is about to quit running" even if screwed in all the way and bottomed. Remember the fuel flow is controlled here by the pilot fuel jet not the pilot air screw. The procedure you describe would be fine if you were adjusting a carburetor which used an idle mixture screw which controlled fuel flow.
Adjustments made to the pilot air screw on a two stroke snowmobile engine are much more subtle and sometimes hard to even detect. the more cylinders you have the more subtle the results are apt to be.

The pilot air screw adjustment and the size of the pilot fuel jet are specified by the manufacturer based on the engine the carb is installed on. If you will refer to the hood sticker or the shop manual you will find a pilot air screw adjustment specified for whatever sled you are working on. Remember these carbs are used on many different engines and the combination of the size of the jet and the amount of bypass air is specific to the application. In the case of the 1996 XLT that is the topic of this thread Polaris recomends the pilot air screw be adjusted to one full turn back from lightly bottomed and a #35 pilot fuel jet to control the idle fuel mixture. They recommend no other adjustments be performed to the pilot air screw after that setting is acheived.
Of course the screw and jet may need to be changed from the factory recommended settings if the sled were to be used at higher altitudes and or for the use of oxygenated fuels. In that case the main jet size as well as other changes should be made also.





I also don't understand what you are acomplishing by raising the idle speed to syncronize
the carbs?

As I stated earlier the syncronizing procedure is done so the slides are all at the same height. This is a two part operation.

In the first step the slides are adjusted so the slides are exactly the same when the throttle is released and the cables are slack the slide height is now being controlled by the slides bottoming against idle stop screws. The adjustment is performed by turning the idle stop screws. The idle speed is adjusted at this time and you ensure the slides are at exactly the same height. The fluid in the mercury sticks will all be level when it is right.
If you elevate the idle before doing this then you would have to reset the idle to specified rpm and resync the slides a second time . To me this is just adding a step to the process.

The second step is to ensure the slides are at the same height and syncronized when the throttle is applied and the cables are now controlling the height of the slides. I like to block the throttle partially open at the thumb lever with a match book or something of similar thickness so it does not move while I am making my adjustments. You then adjust the slides they are the same height and tthe carbs are open exactly the same. The adjustment is performed by turning the cable barrels at the top of the carbs which will shorten or lengthen the throttle cable in question. Once again you ensure the fluid in the mercury sticks are all the same level.

After the cables are adjusted to the exact same length the throttle is released and the Cable slack is adjusted to specification (0.10" to 0.30" )
by turning all the barrels exactly the same amount of turns and locking them in place. The throttle is then applied again and you ensure that the fluids in the tool are still level and you have not put the carbs out of sync by adjusting the cable slack. In this way you have ensured the idle speed is correct and all the carbs are syncronized and flowing the same at idle as well as at speed.



I re read your previous post and now I think I understand where you are coming from re the syncronization and idle rpm. It would seem you are basing this on procedures used for multi cylinder carbs which would be installed on street bikes. Unless I am incorrect most street bikes use a single throttle cable and a solid linkage across all the carbs. So the syncronization procedure is different because all the carbs are linked it is only necessary to sync them together and not individually. So you can sync them at idle speed or if you prefer at elevated idle speeds for more accuracy. There is no need to syncronize each individual carb at idle speed and also off idle as is the case for a snowmobile as there is usually only one idle stop screw on the linkage. As you re adjust that one idle screw back to base idle you will have not altered the syncronization and it would not have to be rechecked. You must consider that bikes and sled are somewhat different and require different procedures to acheive the same goal.