more jetting ?

[bigneily]

how do you tell if your pilot jet is maybe too fat or lean etc ? my sled seems to run rich while idleing(irregular idle) 98 summit x / 44mm roundslides with ufo's i already dropped the pilots to 25's, but was wondering how to tell if i need to go leaner? thanx for any input men....

 

[Idcatman1]

pilot jetting

A few years ago i put some UFOs in a 600 ZRT Cat and also some 600 Powder Specials. I think I ended up with #10 pilots in them because they would hardly pull themselves from a dead stop. If you can start your sled on a cold morning and it will idle right off the bat without having to play with the choke or primer it is probably on the rich side. It will also get worse as the engine warms up, and will smoke and sound a little muted. If too lean you will have to play with the choke to keep it running on a cold start. It will also cough or maybe even backfire when you give it throttle. A lean pilot will get better as the engine warms up and also if you flip the choke or hit the primer. Hope this helps.

 

[storeytellin]

Not the expert here, but I would not mess with your jetting based on what the sled is doing at an idle. Plug color and piston wash is a better tell as to what your jetting needs are. You have an idle adjust screw on your carbs that you can mess with if that is your only trouble. I believe the 98's had the rotary valve on them, timing is important. How does the sled run when you are WOT?

 

[bigneily]

the sled runs really well all through the power range, the only thing is the bad idle after it is warm (real heavy gas odour when idleing also) i phoned thunder products they told me to run a 17.5 pilot right off the bat, but i was told from anoyther knowledgeable sled guy that i might be askin for trouble with that lean of a pilot. thats why i was wondering if their is a safe way to tell if i can go leaner on the pilot..... p.s the iidle is worse at elevation sometimes when your on the throttle and slow down and stop for a break it won't even idle at all i moved the needle clip one position leaner but it didn't make a noticeable difference...

 

[storeytellin]

Might not hurt to jump this over to the Skidoo forum for more help also.

 

[summit800]

my 96 670 with ufo and jaws pipes I had 12 pilots in it , Did you drill the needle jet like they tell you too???? I can tell you now that the 17.5 probly will work , but I bet you'll be on the upper knotch on the needle jets

 

[Speednutt]

If the manufacture of the UFO's told you to jet down, then that is what you need to do. Dont mess with your idle adjust screw on your carbs. Thunder products knows their stuff.

If you have a rich condition while idling, that is from a too large pilot. The pilot and only the pilot jet supply fuel during the idle curcuit. Keep in mind that what summit800 stated about drilling out your needle jet. The pilot does control the idle curcuit, but it also supplies about 10% of fuel flow at wide open.

Since you are reducing the pilot jet down in size, you must increase the needle jet size to accomodate for the extra fuel needed now at wide open.

With your evaluation of higher altitudes, it just solidify's the theory that your pilot jet is way too rich. the higher you go, the less fuel you need.

Good luck.

 

[AKtoad]

When riding at your normal elevation and when the sled is warm blurp the throttle and let off. If the idle hangs there for a split second and slowly comes down it is lean (this could also be from a cracked carb boot or cracked y-pipe as well) and you would go up a pilot, if the idle comes down quick and does not bog down you are good if it bogs down and almost dies then you are to rich. The pilot is only good for idle to 1/4 throttle then the needle and then the main.

I run 22.5 pilots with 430 mains from sea level to 3500 feet here in AK with my 800 HO (Yes there is snow at sea level here and we ride from it)

 

[summit800]

You did grind the slides down like they say in the directions

 

[NoSecondChances]

Why are you guys talking about drilling out the needle jets? Just buy the proper ones, they are about $20 each. Cheap insurance for such a precision instrument which could make a big difference in how your motor runs, especially if you are off a fraction of an inch with the drill.

bigneily - maybe try the air screw first, this will probably help things out before you start playing with the pilot jets. It seems like these UFO's have caused more jetting problems for you than maybe they are worth?

 

[bigneily]

thanx for all the replies men first off yes the slides are ground to thunder products spec's, this might be stupid but what are needle jets and where are they found, will the size that is in my sled be marked on them? thanx again...