I dont get it... (about nitro tuning, everyone is welcome! i need to know more!)

[:D lmao]

Q1: What does LSN do, does it effects low rpm or low throttle? if i blip the gas ones (from zero to wide-open quickly, then immediately releasing the trigger) is it HSN or LSN?
Q2: does HSN affects idle?
Q3: the relation between LSN and idle crew, i can affect idle by either leaning the LSN or adjusting the idle screw, but which way is the best? or should i adjust both proportionally?
Q4: share the experience you've earned during tuning

All questions don't need to be answered

 

[WVNed]

You are adjusting a carburetor. A carburetor mixes an appropriate amount of fuel into an air stream passing threw it.
The low speed needle controls how much fuel goes in at low throttle openings and low air velocity threw the carb and the HSN does when it is mostly open and there is high air velocity.
The idle screw controls the smallest amount you get when the throttle is closed. The gap left determines the minimum amount of air that can go into the engine when the throttle is closed. Once tuned the LSN is set to mix the right amount of fuel into this air so the engine will idle.

The LSN is harder to set than the HSN on most engines. For that reason the HSN is set first. It can be tuned to a particular temperature you want the engine to be after a wide open pass with the engine fully warm. A new engine may be bound up enough that it will not idle well until fully or mostly broken in. You may be wasting your time trying for a low idle until the engine has been run for a few tanks at least.

The HSN does affect the idle when you close the carb because it determines how much fuel got into the engine before you closed the carb slide and cut the air off. This fuel has to be used before you see and hear the actual LSN needle settings take over. Usually you get a high idle that then drops to a low idle after a few seconds.

While tuning there are 2 ways an a engine can die. On is from too much fuel and the other too little. They sound different. They also determine if you need to prime on restart or clear the fuel out.


That is like 10% of it but hope that helps

Once you do get it tuned you shouldnt have to touch the needles much unless you change fuel or the temp changes quite a bit since you last ran the car.

The needles are sensitive. A tiny turn is a big change. A 1/4 turn can go all the way passed the setting you were trying to find and go from a car that runs poorly from being to rich to one that is now too lean

When it is colder you engine will need to be set slightly richer and hotter slightly leaner. Cold air is more dense and hot less.

 

[:D lmao]

You are adjusting a carburetor. A carburetor mixes an appropriate amount of fuel into an air stream passing threw it.
The low speed needle controls how much fuel goes in at low throttle openings and low air velocity threw the carb and the HSN does when it is mostly open and there is high air velocity.
The idle screw controls the smallest amount you get when the throttle is closed. The gap left determines the minimum amount of air that can go into the engine when the throttle is closed. Once tuned the LSN is set to mix the right amount of fuel into this air so the engine will idle.

The LSN is harder to set than the HSN on most engines. For that reason the HSN is set first. It can be tuned to a particular temperature you want the engine to be after a wide open pass with the engine fully warm. A new engine may be bound up enough that it will not idle well until fully or mostly broken in. You may be wasting your time trying for a low idle until the engine has been run for a few tanks at least.

The HSN does affect the idle when you close the carb because it determines how much fuel got into the engine before you closed the carb slide and cut the air off. This fuel has to be used before you see and hear the actual LSN needle settings take over. Usually you get a high idle that then drops to a low idle after a few seconds.

While tuning there are 2 ways an a engine can die. On is from too much fuel and the other too little. They sound different. They also determine if you need to prime on restart or clear the fuel out.


That is like 10% of it but hope that helps

Once you do get it tuned you shouldnt have to touch the needles much unless you change fuel or the temp changes quite a bit since you last ran the car.

The needles are sensitive. A tiny turn is a big change. A 1/4 turn can go all the way passed the setting you were trying to find and go from a car that runs poorly from being to rich to one that is now too lean

When it is colder you engine will need to be set slightly richer and hotter slightly leaner. Cold air is more dense and hot less.

thank you! very useful!

 

[Johnny1369]

Hey, thanks a lot. I was just reading through this thread that was very helpful. I do have a quick question. When you buy a brand new carburetor is it already set?

 

[WVNed]

That's something I have never done so I don know.

 

[tudordewolf]

Hey, thanks a lot. I was just reading through this thread that was very helpful. I do have a quick question. When you buy a brand new carburetor is it already set?

It's customary for factory settings to be set for break-in, as if you're going to be running in a new engine with your new carburetor, which also means it'll be tuned about as rich as it can go. I've never heard of someone needing to tune RICHER than factory settings, unless they've got an air leak or something else interfering with a proper tune.

In my experience it may even be tuned too rich to start depending on your engine / weather, just because it's so much better to start off too rich than too lean.

On every carburetor I've encountered so far, the low-speed needle is at its factory setting when its head is flush with the collar around it. Some high speed needles are like that too, but some aren't. Often you can find published values as a number of turns "out" from the needles being screwed all the way in.

 

[cbaker65]

You are adjusting a carburetor. A carburetor mixes an appropriate amount of fuel into an air stream passing threw it.
The low speed needle controls how much fuel goes in at low throttle openings and low air velocity threw the carb and the HSN does when it is mostly open and there is high air velocity.
The idle screw controls the smallest amount you get when the throttle is closed. The gap left determines the minimum amount of air that can go into the engine when the throttle is closed. Once tuned the LSN is set to mix the right amount of fuel into this air so the engine will idle.

The LSN is harder to set than the HSN on most engines. For that reason the HSN is set first. It can be tuned to a particular temperature you want the engine to be after a wide open pass with the engine fully warm. A new engine may be bound up enough that it will not idle well until fully or mostly broken in. You may be wasting your time trying for a low idle until the engine has been run for a few tanks at least.

The HSN does affect the idle when you close the carb because it determines how much fuel got into the engine before you closed the carb slide and cut the air off. This fuel has to be used before you see and hear the actual LSN needle settings take over. Usually you get a high idle that then drops to a low idle after a few seconds.

While tuning there are 2 ways an a engine can die. On is from too much fuel and the other too little. They sound different. They also determine if you need to prime on restart or clear the fuel out.


That is like 10% of it but hope that helps

Once you do get it tuned you shouldnt have to touch the needles much unless you change fuel or the temp changes quite a bit since you last ran the car.

The needles are sensitive. A tiny turn is a big change. A 1/4 turn can go all the way passed the setting you were trying to find and go from a car that runs poorly from being to rich to one that is now too lean

When it is colder you engine will need to be set slightly richer and hotter slightly leaner. Cold air is more dense and hot less.

Awesome explanation ,I could not of said it any better!..........

 

[Johnny1369]

It's customary for factory settings to be set for break-in, as if you're going to be running in a new engine with your new carburetor, which also means it'll be tuned about as rich as it can go. I've never heard of someone needing to tune RICHER than factory settings, unless they've got an air leak or something else interfering with a proper tune.

In my experience it may even be tuned too rich to start depending on your engine / weather, just because it's so much better to start off too rich than too lean.

On every carburetor I've encountered so far, the low-speed needle is at its factory setting when its head is flush with the collar around it. Some high speed needles are like that too, but some aren't. Often you can find published values as a number of turns "out" from the needles being screwed all the way in.

Hey, thanks a lot for that. I appreciate the input and the knowledge

 

[cbaker65]

Once a person has the Hsn dialed in with the idle gap ,the Lsn is not hard to figure out!
A simple pinch test can determine how close the Lsn can be tuned ,the pinch test
is not a tuning point ,but it will tell you if your too lean or too rich on the Lsn!

You do a full WOT pass an bring it in an pinch the fuel line before the fuel nipple ,
if the engine dies with in 4 to 5 seconds ,then you are good on the Lsn tune ,
If it lingers an dies after 5 seconds ,then you are a little too rich ,can be a little leaner!
If it dies with in 2 to 3 seconds in a real quick abrupt die ,then you are too lean!..