99 SX600 Pilot Screw Setting

Racing666

Racing666

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Jan 6, 2009
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So, my dilemma continues. No power, boggy on throttle, and then when it reaches a certain rpm it takes off like a bat out of hell. Can't just putt along or it pukes on itself. Carburetors are SPOTLESS. I have just a couple of questions.

1) What exactly is the pilot screw on the carburetor adjusting? I mean I know its for the pilot circuit but is it adjusting fuel or air?

2) I have tried 2 1/2 turns out and 1 3/4 turns out from lightly seated. 1 3/4 out and it was doggy and sounded like it was skipping and wouldn't rev up. 2 1/2 turns out and it runs alright but if you try to rack on the throttle it backfires. If you choke it, it revs up like it should but wont idle and eventually pukes out and dies.

3) What should that screw be set at? I have not been able to get a definitive answer as to what the stock setting on this is? Should I try 1 turn or 1 1/4 out?

HELP!!

Thanks in advance!
 
You can find the stock specs from the home page. Click on tech pages link and then on snowmobile tech link, all your carb settings are right there. I had the same symptoms on my 98 600, low end bog and backfire which the choke would clean up. Opened the air screw 2 turns and raised the needle one notch and that was it. Before any adjustments make sure your not sucking air around the boots and reed valves.
 
Thanks ironman. Didn't know that feature existed. I am a little confused though about what it says to do. It lists "fuel screws" - 2 and "pilot air jet" - 1. As far as I know there is only 1 screw and it is on the airbox side on the bottom of the carburetors and that is the pilot air adjustment. What are they talking about a "fuel screw"?
 
man it sounds like your pilot jets or circuits are plugged,when you say with choke on it revs up then dies is that at wot? on different carbs the screw does different things usualy you adjust fuel when it is on the bottom of carb and you adjust air when its on the side hope this helps
 
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^^ No, I can hold it at WOT and it stays at a constant RPM with choke on. Doesn't seem like its all the way at top speed but it does hold it's RPM well with the choke on full. When I let off the throttle is when it starts spitting and sputtering.

Pilot Jets are all 42.5's. #1 main is 136.3 and #2+#3 are 134's. Pilot circuit is clean, I blew compressed air through all 3.

When I had it at 1 3/4 out, it acted like it was lean. So, if I turned the screw OUT more to 2 1/2 shouldn't it have gotten better and not worse? If I choke it full it revs up beautiful. I truly am lost here as to what to try.

My biggest problem is that I think it's really lean being that if I choke it, it wants to rev up. Not knowing which way to go with that screw and what it is adjusting (fuel or air) is hurting.

I'm going to try 1 turn out tomorrow morning and see what happens. I have gotten to the point where I can have the carburetors off and back on in about 15-20 mins. BTW, nice job Mikuni and Yamaha for choosing to put the screw where it is.. Grrr... LoL
 
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make sure you dont have a air leak where carbs mount to motor or reeds or crank seals check your floats take them off and look at them and the needles and seats take them out and blow through them, check the jet in the bore on the air box side, check puls hose to fuel pump and fuel pump, fuel is it fresh? when did this start ? while there off check sync, when you cleaned carbs did you take out the pilot jets and blow throw jet and passege seperatly? same with the main and the needle jets, the choke on the sled doesnt restriced air it opens a fuel port so if the choke helps you have a fuel restiction in carb or a bad air leak towards the motor or pluged exhaust or weak motor? stock setting for that screw i think is 2 turns from lite seat,1 turn is to lean
 
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All the holes in the jets are clean. When I spray carburetor cleaner into the pilot passage, it comes up into the throat of the carburetor on all 3. Main jets and passages are all clear. Carbs are in sync, floats are all set correctly. Fuel is 2 days old. Compression in all 3 cylinders is 130psi. Reed cages, reeds and boots are all new and tight. Fuel pump is new as well. What kind of bothers me, is that with the fuel lines off the carburetors I can pull the sled over and fuel doesn't shoot out of the lines but the fuel bowls are always full when I pull them off. I'm going to try and do some video today of how it runs and what i've changed.
 
pulling it over the fuel will just dribble, when did this start? does it idle? there are holes in the side of the pilot and the needle jet so you would be able to spray through and still be pluged on the side
 
It's definitely related to the float level. I got to looking and thinking. I set it so the floats would stay open longer to allow more fuel into the bowls and it made a DRASTIC change. I would like to set them properly but I have no idea what their talking about to adjust them.
 
did you look at fuel pump in another thread the dude found ice just a thought, hoses on right? fuel filter pluged? when you set them there is a spring pin on the end of the needle hold carb so the float just contacts this and doesnt push it in
 
I bent the tab that the float valve clip slides on so that it opened further. I initially did it just to see what would happen. I think the whole problem with the sled lies in the float adjustment. I just wanna set it right now but I don't know what they mean when they say 13.3mm? 13.3mm from what?
 
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While I had it apart today, I tried to take the slide out so I could see where the clip on the needle is, but we couldn't figure out how to get it out? What's the trick?
 
well on the float there are two adjustment tangs one that adjusts height one that adjusts drop, the one closest two bowl edge is for drop and the one over the needle is for height, the measurement is from the bowl mating surface(some with gasket some without) to top edge (farthest edge from mating surface) or noted spot, now to check needles you take off cover then turn throttle shaft to bring up slide and you will see the little screws you must take them out and under that arm is where they sit, i beleive it tells you in tech section
 
it should be in carb settings in manual or i measure the distance to bowl bottom or longest un obstrucked drop if there is something it could jamb on and set it there, you just dont want the needle two drop out or jamb when the float is droppped i aways give it the max, because too little it will run lean on top. probably just me but if i dont have a spec thats what i ve done for years
 
Still having some issues but its definitely rideable. I have to "roll" into the throttle though. If I try to just get on it hard or pin it, it hesitates for 1/2-3/4 second then takes off. If I give it choke, it revs up like it should. I know what your going to say. "Carbs Dirty" but I am 100% sure they are clean. Float heights are set to specs as well. As of right now, I am 2 turns out on the fuel screw. If I give it choke and it revs up better, that would indicate a "lean" condition in the pilot circuit. Pilot jets are stock. I would like to get rid of that hesitation. Should I go further on the fuel screw to say 2 1/4 - 2 1/3 turns out?
 
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