General Discussion Forum

So i've been reading some responses about jets on the forum, and i just dont undestand the difference between say a pilot jet that is 38, compared to a 42 for example? Why would it make a difference and how exactly?

Kinda hopin Skipkh can answer this one lmao, he seems to know ALOT, but any help is appreciated!!    
The best source of protein is Raw Eggs~!

Ah Skip - he's full of it - don't listen to him!!!

The number on the jet indicates how much fuel it will flow in a given amount of time.  A 38 pilot has a smaller orifice, therefore it will flow less fuel per minute than a 42 pilot (for example).  The larger the number on the jet, the more fuel it flows per minute.

When a jet is too small, it creates a lean mixture (engine isn't getting enough gas for the amount of air it's taking in). When a jet is too large, it creates a rish micture (engine is getting too much fuel for the amount of air it's taking in) and you need to install a smaller jet.

Imagine a solid piece of brass.  A #38 pilot has a hole drilled in it with a drill bit.  A 42 pilot has a hole drilled in it with a slightly larger drill bit.  Therefore the hole through the center of a 38 pilot is a tiny bit smaller than the hole through the center of a 42 pilot.  
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I had actually been wondering the same thing. LOL  
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Dam it skip! I was just going to give my in depth knowledge and plagiarism on this.
Dohhhhh!  
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Ruff!

In depth knowledge? How deep is that?! HA!!
*jokes*  
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Think 'Middle of the Atlantic' deep.  Woods - ya would have wowed them!  I just got here first..  
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ahh, now i get it  

lol thanks skipkh

Just one question though,  wouldnt unscrewing say a 38 pilot jet let in enough fuel so that you wouldnt need say a larger pilot jet?

and you can upgrade any carb with bigger jets correct?  
The best source of protein is Raw Eggs~!

o..i think i caught myself here...

correct me if im wrong, i havnt exactly taken out my pilot jet yet, kinda new to this, is there 2 holes or one?

So when u unscrew it then u can chose between either holes for the fuel to flow through?

Am i kinda on the right track here?    cus if i am then i see the logic behind having a greater number, thus larger holes.  
The best source of protein is Raw Eggs~!

or am i thinking of the needle jet...isnt that the same thing?? oooohh, now im confused?/??????      
The best source of protein is Raw Eggs~!

OK - you can't 'unscrew' the pilot jet and change the hole in the center of it.  When you install it, you must screw it in all the way or it will fall out.  Now, you CAN adjust the pilot circuit by turning the airscrew in or out.  The pilot jet and the pilot screw together make the pilot circuit.  You get the jetting close with the pilot jet, and then fine tune it with the screw.  If you have to turn the screw all the way in, or more than 3 turns out, that's when you need to put in a different size pilot jet.
For the record, the pilot jet has many holes - I was trying to simplify when I said one bored hole.  The center hole is different among different sized pilots, but the side holes are all the same, I believe.

The needle has clip positions, so you can raise or lower the clip to change the mixture.  
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its like a screw that has a hole going through the middle. unscrewing it has nothing to do with the size of the hole. the bigger jet has a bigger hole going through it.  
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Ride 2 strokes, buy 2 strokes, save the 2 stroke.

1998 cr125
2002 cr80

ah!    

thanks!! so you have to put the pilot jet all the way in, but u can adjust the pilot screw. and the greater number the more fuel it lets in.

i feel much better now, thanks guys.  
The best source of protein is Raw Eggs~!

you mean air screw. turning the air screw in allowes less air in at idle to 1/4 thottle. turning the air screw out allowes more air in. and yes the pilot jet should be turned in all the way. it would suck if the pilot jet wiggled itself loose while your riding.  
______________________________
Ride 2 strokes, buy 2 strokes, save the 2 stroke.

1998 cr125
2002 cr80

so theres a pilot jet, but the screw attached to it is the air screw?

c i thought u could adjust how much fuel goes through the carb with  say turning the pilot jet, but now i think i understand, the pilot jet does let in extra fuel, by the holes but instead of adjusting a screw for fuel, you adjust a screw for air, so there is an air screw on the pilot jet? and u can control how much air is let through, btw is this before or after the venturi?

am i catching on?  
The best source of protein is Raw Eggs~!

Sort of

The pilot jet is at the bottom of the carb and it draws fuel out of the float bowl.  The airscrew covers up an air passage that joins with the stream of fuel coming through the pilot jet.  The more you unscrew the airscrew, the more air it lets through the passage, and the leaner the mixture is.

Yes - this circuit ultimately feeds the venturi.  However, it's best to consider the pilot circuit as a mini carb within your carb.  In the main carb, the raising of the slide (by opening the throttle) controlls the amount of air that comes through. In the pilot circuit, it has a separate air passage, and the amount of air coming through it is controlled by the air screw. When you turn the throttle, you are making a bigger opening in the venturi for air to flow through (by raising the slide).  Under the same principle, when you turn the airscrew out, you are opening the pilot passage, allowing more air through.

Get it?  Good!

Pop quiz next week - bring a #2 pencil  
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