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Discussion Starter · #1 ·
Being reading some of you posts ( including) overhauling the skidoo 40mm carbs.
I do not wnat to completely strip the carbs apart...yet, except changing pilots, mains, adjusting needle and fuel screw.
I have a common problem on my 02 mxz 800.
It idles high at warm up and during stops while riding.
Easy adjustment is to flip the choke and the idle drops down.
As I am still changing jets...
What is the the first initial adjustment/mod to let those carbs drop down to idle when coming to idle?? what do you think is the first try fix to inhibit this ( problem probably is friction based
What do you think would be the likely sticking point? and adjustment necessary?
Would appreiciate your input
 

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journeyman sled/motorhead
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Being reading some of you posts ( including) overhauling the skidoo 40mm carbs.
I do not wnat to completely strip the carbs apart...yet, except changing pilots, mains, adjusting needle and fuel screw.
I have a common problem on my 02 mxz 800.
It idles high at warm up and during stops while riding.
Easy adjustment is to flip the choke and the idle drops down.
As I am still changing jets...
What is the the first initial adjustment/mod to let those carbs drop down to idle when coming to idle?? what do you think is the first try fix to inhibit this ( problem probably is friction based
What do you think would be the likely sticking point? and adjustment necessary?
Would appreiciate your input[/b]
if changing the idle mixture does not help, richen the pilot jet to drop the idle. flipping the choke richens the fuel mixture to drop the idle. as soon as it is burned off it idles up.
 

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if changing the idle mixture does not help, richen the pilot jet to drop the idle. flipping the choke richens the fuel mixture to drop the idle. as soon as it is burned off it idles up.[/b]
Exactly !,

BRP equips all the carbs with 17.5 Pilots which become too lean once the throttle slides have some looseness in them. The first step is to try 20 pilots with the same initial fuel screw adjustment then dial in in (lean) until the idle reaches maximum speed. After the engine stabalizes back out the fuel screw 1/2 ~ 3/4 turn.
 

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Exactly !,

BRP equips all the carbs with 17.5 Pilots which become too lean once the throttle slides have some looseness in them. The first step is to try 20 pilots with the same initial fuel screw adjustment then dial in in (lean) until the idle reaches maximum speed. After the engine stabalizes back out the fuel screw 1/2 ~ 3/4 turn.[/b]
When you refer to the fuel screw, what exactly do you mean? Are these flat slide carbs you are refering to? My '00 MachZ has 38 flats, is there a 'fuel screw' on them? Is the 'fuel screw' the same thing as what I refer to as the air screw (As per Olav Aaen's Carb Tuning Handbook) which controls the passage way or 'circut' directly associated with the pilot jet?
 

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journeyman sled/motorhead
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When you refer to the fuel screw, what exactly do you mean? Are these flat slide carbs you are refering to? My '00 MachZ has 38 flats, is there a 'fuel screw' on them? Is the 'fuel screw' the same thing as what I refer to as the air screw (As per Olav Aaen's Carb Tuning Handbook) which controls the passage way or 'circut' directly associated with the pilot jet?[/b]
I hate to speak for doc, but I am sure he is refering to the air screw you speak of.
 

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Discussion Starter · #6 ·
Exactly !,

BRP equips all the carbs with 17.5 Pilots which become too lean once the throttle slides have some looseness in them. The first step is to try 20 pilots with the same initial fuel screw adjustment then dial in in (lean) until the idle reaches maximum speed. After the engine stabalizes back out the fuel screw 1/2 ~ 3/4 turn.[/b]
I am already running 20 pilots, at 1000 ft., temp averages around -20- -30 Celcius inwinter, but have tried the 15's. Fuel screws are at around 1 3/4.
Running CPI hooded sheilds with a polaris needle, not sure of the taper, at the 4th clip
With these specs. , I dont think I should fatten the fuel screw, or not?????
!ADVICE , please!!
If I was to lean out the fuel screw from there would this be a possible fix to the idle sticking? Or should I fatten it up more than you suggest?
In other words what is causing the high sticking idle, specifically?????

Thanks for the response, hope for a feedback,
cheers, LetsdoIt
 

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The fuel screw I am referring to is the Idle mixture screw which allows more or less pre emulsified fuel from the pilot circuit into the airflow from a bleed hole ahead of the needle jet. As you have mentioned (Dooman too) that you flip the choke to bring down the idle speed when coming to a stop warm. The issue here is not the throttle slides failing to return to the idle stop, it's probably a lean condition proved by you adding fuel with the choke (enrichment circuit). I would first check the condition of the carb boots and reed valve gaskets, then move on to the hoses which supply pulse to the fuel pump and DPM (if equipped). Look at all the nipples on the carb side of the motor for cracks or loose fit. Next check the choke cable adjustment for tightness and binding as I have seen many carbs have the low speed circuit adjusted for good low speed performance only to find it was done with the enrichment plungers off their seats. Lastly, check the throttle slides for fit, sometimes the slide wear out and cause lean idle / low speed issues. Do yo have someone you can borrow a carb rack from to test the motor with. Most TMs are similar and save jetting are interchangeable.
 

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Discussion Starter · #9 ·
The fuel screw I am referring to is the Idle mixture screw which allows more or less pre emulsified fuel from the pilot circuit into the airflow from a bleed hole ahead of the needle jet. As you have mentioned (Dooman too) that you flip the choke to bring down the idle speed when coming to a stop warm. The issue here is not the throttle slides failing to return to the idle stop, it's probably a lean condition proved by you adding fuel with the choke (enrichment circuit). I would first check the condition of the carb boots and reed valve gaskets, then move on to the hoses which supply pulse to the fuel pump and DPM (if equipped). Look at all the nipples on the carb side of the motor for cracks or loose fit. Next check the choke cable adjustment for tightness and binding as I have seen many carbs have the low speed circuit adjusted for good low speed performance only to find it was done with the enrichment plungers off their seats. Lastly, check the throttle slides for fit, sometimes the slide wear out and cause lean idle / low speed issues. Do yo have someone you can borrow a carb rack from to test the motor with. Most TMs are similar and save jetting are interchangeable.[/b]
put new vforve and boots and reeds in last year. still pefect shape last week.
willcheck hoses in a couple days. thumbdoctor..i hate paying BRP pricing. any suggestings on where to get new hosw. amd what s the exact sizes? Diameter wise?
Plus , what play sould I have for the choke cable adjustment?
Appreciate your input
 

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Aren't there two passages into the main air stream (venturi) associated with the pilot jet circut, one just before the the rear lip of the slide and one after? Just trying to understand this better...
 

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So was I wrong about the two passages into the ventrui associated with the pilot jet circuit?[/b]
Yes you are correct, there are two passages in the pilot circuit controlled by the pilot jet. The first is the main orifice)closest to the throttle slide) and the second (called the bypass) comes into play from about 1/8 ~ 1/4 throttle opening.
 

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Yes you are correct, there are two passages in the pilot circuit controlled by the pilot jet. The first is the main orifice)closest to the throttle slide) and the second (called the bypass) comes into play from about 1/8 ~ 1/4 throttle opening.[/b]
Thanks Thumbdoctor for clarifying!
 

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Discussion Starter · #15 ·
Wil try these suggestings, still would like snow.
Skidoo called yesterday, the new 800X renegade is in.
Will be a good winter hopefully, the last five were kick ### for snow!
 
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