Jets
- Thread starter canalcat
- Start date
butre
Well-Known Member
what's your elevation?
I can only give you a starting point and you should work up or down from there.
I can only give you a starting point and you should work up or down from there.
Steve Best
Well-Known Member
Need carb type (picture would really help) elevation and your temperature to even hazard a guess,
and then we would still be only guessing and likely wrong...
The jets come from all over the world and are a simple thing to make.
Their sizing is supposed to be to a standard (flow rate) but are often made with little quality control.
To raise the stakes, 2 strokes are a balancing act.
They make more and more power the leaner you go,
until you go too far, and then you burn a piston and damage your cylinder.
So how do know what to use for a jet?
First, you need to understand something about carbs. The NT carb has 3 jet circuits"
1) pilot jet, does idle mixture and low speed. It is fixed in this carb so don't worry about it.
2) the needle (jet). Does mid-throttle drivability. The jet is in the carb body, you adjust the needle up or down with a clip.
3) the main jet. For Wide Open Throttle (WOT) full power. This affects your power, fuel mileage and reliability.
The NT carb mainly seems to come with a #70 main jet and typically this is a bit rich but works ok.
Many of us have found if we install a 68 or 65 jet (they do not come in every number), our engine works even better.
If we go too low, the combustion burns too hot and can burn up the piston and cylinder.
So we go down one size at a time and keep checking the sparkplug to be sure it is not too lean.
The yellow circled sparkplug is too lean.
The plug in the center is too rich and little plug on the left is just right.
So you figure out if you are running rich or lean at WOT.
Then find what you have in your carb for a jet, and you order a set of jets to experiment with.
What if your jet is not marked? If it is an NT you can assume it is a #70 and order a 68 and 65.
But when they arrive, compare them with a sewing needle (use the depth the taper goes in) to compare.
Put the new jet in and go for a WOT ride to see how the next smaller jet works.
Check the plug if it is safe.
That is the process.
Steve
and then we would still be only guessing and likely wrong...
The jets come from all over the world and are a simple thing to make.
Their sizing is supposed to be to a standard (flow rate) but are often made with little quality control.
To raise the stakes, 2 strokes are a balancing act.
They make more and more power the leaner you go,
until you go too far, and then you burn a piston and damage your cylinder.
So how do know what to use for a jet?
First, you need to understand something about carbs. The NT carb has 3 jet circuits"
1) pilot jet, does idle mixture and low speed. It is fixed in this carb so don't worry about it.
2) the needle (jet). Does mid-throttle drivability. The jet is in the carb body, you adjust the needle up or down with a clip.
3) the main jet. For Wide Open Throttle (WOT) full power. This affects your power, fuel mileage and reliability.
The NT carb mainly seems to come with a #70 main jet and typically this is a bit rich but works ok.
Many of us have found if we install a 68 or 65 jet (they do not come in every number), our engine works even better.
If we go too low, the combustion burns too hot and can burn up the piston and cylinder.
So we go down one size at a time and keep checking the sparkplug to be sure it is not too lean.
The yellow circled sparkplug is too lean.
The plug in the center is too rich and little plug on the left is just right.
So you figure out if you are running rich or lean at WOT.
Then find what you have in your carb for a jet, and you order a set of jets to experiment with.
What if your jet is not marked? If it is an NT you can assume it is a #70 and order a 68 and 65.
But when they arrive, compare them with a sewing needle (use the depth the taper goes in) to compare.
Put the new jet in and go for a WOT ride to see how the next smaller jet works.
Check the plug if it is safe.
That is the process.
Steve
gary55
Well-Known Member
Do you mark the end of the needle with a sharpie then measure the point of the taper where the ink rubs off with a little spinning of the needle?Need carb type (picture would really help) elevation and your temperature to even hazard a guess,
and then we would still be only guessing and likely wrong...
The jets come from all over the world and are a simple thing to make.
Their sizing is supposed to be to a standard (flow rate) but are often made with little quality control.
To raise the stakes, 2 strokes are a balancing act.
They make more and more power the leaner you go,
until you go too far, and then you burn a piston and damage your cylinder.
So how do know what to use for a jet?
First, you need to understand something about carbs. The NT carb has 3 jet circuits"
1) pilot jet, does idle mixture and low speed. It is fixed in this carb so don't worry about it.
2) the needle (jet). Does mid-throttle drivability. The jet is in the carb body, you adjust the needle up or down with a clip.
3) the main jet. For Wide Open Throttle (WOT) full power. This affects your power, fuel mileage and reliability.
The NT carb mainly seems to come with a #70 main jet and typically this is a bit rich but works ok.
Many of us have found if we install a 68 or 65 jet (they do not come in every number), our engine works even better.
If we go too low, the combustion burns too hot and can burn up the piston and cylinder.
So we go down one size at a time and keep checking the sparkplug to be sure it is not too lean.
The yellow circled sparkplug is too lean.
The plug in the center is too rich and little plug on the left is just right.
So you figure out if you are running rich or lean at WOT.
Then find what you have in your carb for a jet, and you order a set of jets to experiment with.
What if your jet is not marked? If it is an NT you can assume it is a #70 and order a 68 and 65.
But when they arrive, compare them with a sewing needle (use the depth the taper goes in) to compare.
Put the new jet in and go for a WOT ride to see how the next smaller jet works.
Check the plug if it is safe.
That is the process.
Steve
Steve Best
Well-Known Member
No, but that is a good idea.
I measure how much of the sewing needle sticks out of the jet with a vernier.
Your idea is simpler.
(give a man a vernier, every problem needs to be measured)
Steve
gary55
Well-Known Member
It's one of my favorite tools. also handy for metric, fraction, and decimal equivalents. Honestly though I had to look up the word vernier. I wasn't even aware that it was also called that. Old dog learned a new word.
Steve Best
Well-Known Member
Actually what I use these days is dial caliper, which has no vernier scale on it:
Mainly because my old eyes cannot read the vernier any more.
I started out my career as a machinist, so it was always called your "vernier".
Steve
Mainly because my old eyes cannot read the vernier any more.
I started out my career as a machinist, so it was always called your "vernier".
Steve
butre
Well-Known Member
yeah I can't read the verniers anymore either. I definitely like the dial calipers better though, way easier to read even if your eyes are still good.
my eyes are blurry enough that even zoomed in everything from .56 to .66 looks about in line to me. part of that is probably the pixels making it all look aligned, and I don't have any vernier calipers anymore to check with, but I know last time I used them I was struggling to measure things.
my eyes are blurry enough that even zoomed in everything from .56 to .66 looks about in line to me. part of that is probably the pixels making it all look aligned, and I don't have any vernier calipers anymore to check with, but I know last time I used them I was struggling to measure things.
butre
Well-Known Member
know what else I'll never go back to? cheap calipers. my starretts kick ass. totally repeatable and smooth as hell even with the hell I put my tools through
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