Very nearly perfect 2011 XC 300!

[widebear]

Smaller hole= higher air velocity,lower air pressure. This means more fuel siphoned into air stream, smaller jets required . Same principles but in inverse , example, slide cutaway with bigger cutaway 8 or 9 will create higher air pressure , lower velocity and will siphon less fuel to correct that 1/8 to1/3 stumble that has all you poor little lost lambs chasin your tails. You guy's are killin me here.

[Jakobi]

Originally Posted by widebear

Smaller hole= higher air velocity,lower air pressure. This means more fuel siphoned into air stream, smaller jets required . Same principles but in inverse , example, slide cutaway with bigger cutaway 8 or 9 will create higher air pressure , lower velocity and will siphon less fuel to correct that 1/8 to1/3 stumble that has all you poor little lost lambs chasin your tails. You guy's are killin me here.

I understand that a smaller carb will use smaller jets to pull the same amount of fuel. What I was curious about is why if KTM and GG are both using a 36mm pwk ASII, both 300cc, then why does the ktm need a 160ish main, while the gassers need 170ish..

Valid question?? Probably not, but I wouldnt mind hearing a valid answer

[Vindicator]

Originally Posted by Jakobi

I understand that a smaller carb will use smaller jets to pull the same amount of fuel. What I was curious about is why if KTM and GG are both using a 36mm pwk ASII, both 300cc, then why does the ktm need a 160ish main, while the gassers need 170ish..

Valid question?? Probably not, but I wouldnt mind hearing a valid answer

Might be that the internal design of the GG engine requires more gas+oil to have an effective lubrication ?

[ScottyR]

Originally Posted by Jakobi

I understand that a smaller carb will use smaller jets to pull the same amount of fuel. What I was curious about is why if KTM and GG are both using a 36mm pwk ASII, both 300cc, then why does the ktm need a 160ish main, while the gassers need 170ish..

Valid question?? Probably not, but I wouldnt mind hearing a valid answer

Different needles will determine bigger or smaller jets as well.

[GMP]

Look at all the jetting variables on THE SAME BIKE. All three of my 250s preferred different jetting, same basic motor and carb. Change case design, pipe, reeds, fuel, compression, porting, ignition, tolerances, etc. and 10 points on the main is not ridiculous. Its a completely different motor, with a different signature.

[gasgasman]

Originally Posted by Jakobi

then why does the ktm need a 160ish main, while the gassers need 170ish..

It's called "volumetric efficiency". Basically, an engine is an air pump. VE is how much air an engine can process.

The "perfect" air/fuel ratio is 14.7:1 So different engines require different fuel metering/ratio specs.

[lankydoug]

I love the knowledge and intelligent responses found on this forum.

Any who reads the last few posts should realize that when jetting, give your bike what it's asking for and DO NOT copy your buddies jetting. Sure you can compare as a general guideline but tuning your bike to your riding style is like making a fingerprint.

[widebear]

Originally Posted by Jakobi

I understand that a smaller carb will use smaller jets to pull the same amount of fuel. What I was curious about is why if KTM and GG are both using a 36mm pwk ASII, both 300cc, then why does the ktm need a 160ish main, while the gassers need 170ish..

Valid question?? Probably not, but I wouldnt mind hearing a valid answer

To reiterate. I's easy to get hung up on numbers Like Glen pointed out, a ten point change in main jet is not alot. In fact it only equates to only one tenth on a mm per second unit of measurement, example 170 to 172 should read 1.70 mm , 1.72 mm ect. The most profound effect the sizing will have is at a duty cycle of 100% aka w.o.t. basicly nil at part throttle. I know this to be true because as a resulting mistake because of my poor vision without glasses. I accidently put a 115 main, thinking it said 175 in my buddys 300. He rode all day and only on the road section at the end of the ride did it become apparent the something was wrong. Dont be afraid of tuning a carb its just like pleasing the woman in our lives, the principles are the same they just all respond jusy a little differently!

[Jakobi]

Originally Posted by widebear

To reiterate. I's easy to get hung up on numbers Like Glen pointed out, a ten point change in main jet is not alot. In fact it only equates to only one tenth on a mm per second unit of measurement, example 170 to 172 should read 1.70 mm , 1.72 mm ect. The most profound effect the sizing will have is at a duty cycle of 100% aka w.o.t. basicly nil at part throttle. I know this to be true because as a resulting mistake because of my poor vision without glasses. I accidently put a 115 main, thinking it said 175 in my buddys 300. He rode all day and only on the road section at the end of the ride did it become apparent the something was wrong. Dont be afraid of tuning a carb its just like pleasing the woman in our lives, the principles are the same they just all respond jusy a little differently!

Well said and well said by everyone. They are the answers I was looking for