Which way is leaner on midrange carb screw??
09-25-2011, 03:01 PM
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Which way is leaner on midrange carb screw??
I have an older Novarossi .21 engine with a 3 needle carb. Engine runs fairly well but its a little rich in the midrange. Which way do i turn the midrange screw to lean it out? Is it the same as the other two screws? Just wondering if it would be opposite since the midrange adjustment isnt actually a needle like the high and low.
09-26-2011, 05:42 AM
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RE: Which way is leaner on midrange carb screw??
leave midrange needle at factory settings. unless youre a pro at tuning, do not touch it. 99% of people will never touch it because it never really needs to be touched. the midrange rich problem you are having has to do with the LSN or HSN. the midrange needle is extremely tricky to tune, almost always it will mess up your tune completely. usually if you find yourself messing with that needle you have an air leak of some sort.
09-26-2011, 07:57 PM
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RE: Which way is leaner on midrange carb screw??
I did some searching and seems like 90% of people leave it alone as you mentioned. Still wouldnt mind understanding this adjustment better. I found a couple sites explaining how it adjusts the throttle position at which fuel from the high speed circuit is mixed in. Every time you adjust it you also have to adjust the low speed needle the opposite direction to maintain the same low speed mixture.
But I never did find anything about which way to go?
But I never did find anything about which way to go?
09-27-2011, 05:29 AM
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RE: Which way is leaner on midrange carb screw??
ORIGINAL: mmurray70
I did some searching and seems like 90% of people leave it alone as you mentioned. Still wouldnt mind understanding this adjustment better. I found a couple sites explaining how it adjusts the throttle position at which fuel from the high speed circuit is mixed in. Every time you adjust it you also have to adjust the low speed needle the opposite direction to maintain the same low speed mixture.
But I never did find anything about which way to go?
I did some searching and seems like 90% of people leave it alone as you mentioned. Still wouldnt mind understanding this adjustment better. I found a couple sites explaining how it adjusts the throttle position at which fuel from the high speed circuit is mixed in. Every time you adjust it you also have to adjust the low speed needle the opposite direction to maintain the same low speed mixture.
But I never did find anything about which way to go?
lean is in, rich is out.
Midrange needle just doesnt need to be touch IMHO
09-27-2011, 05:30 AM
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RE: Which way is leaner on midrange carb screw??
ORIGINAL: ALISTAIR13
i have always adjusted the low end needle on all my engines and they go fine
i have always adjusted the low end needle on all my engines and they go fine
09-27-2011, 07:55 AM
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RE: Which way is leaner on midrange carb screw??
Read this article on tuning. it is a very long read but well worth it if you want to understand tuning better. I have it saved in my favorites.
http://hypercentral.18.forumer.com/a...e_post120.html
http://hypercentral.18.forumer.com/a...e_post120.html
09-29-2011, 11:11 PM
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RE: Which way is leaner on midrange carb screw??
ORIGINAL: jmaxey51
not really. you set the LSN first and very seldom touch it again. its usually just tiny adjustments on the HSN, half hour adjustments if that if you are close to tune.
lean is in, rich is out.
Midrange needle just doesnt need to be touch IMHO
ORIGINAL: mmurray70
I did some searching and seems like 90% of people leave it alone as you mentioned. Still wouldnt mind understanding this adjustment better. I found a couple sites explaining how it adjusts the throttle position at which fuel from the high speed circuit is mixed in. Every time you adjust it you also have to adjust the low speed needle the opposite direction to maintain the same low speed mixture.
But I never did find anything about which way to go?
I did some searching and seems like 90% of people leave it alone as you mentioned. Still wouldnt mind understanding this adjustment better. I found a couple sites explaining how it adjusts the throttle position at which fuel from the high speed circuit is mixed in. Every time you adjust it you also have to adjust the low speed needle the opposite direction to maintain the same low speed mixture.
But I never did find anything about which way to go?
lean is in, rich is out.
Midrange needle just doesnt need to be touch IMHO
09-30-2011, 11:04 AM
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RE: Which way is leaner on midrange carb screw??
ORIGINAL: Foxy
On the contrary, the part you bolded is exactly correct. I agree that most people should never touch it, but that bold sentence is gthe most important thing anyone needs to know before messing with it.
ORIGINAL: jmaxey51
not really. you set the LSN first and very seldom touch it again. its usually just tiny adjustments on the HSN, half hour adjustments if that if you are close to tune.
lean is in, rich is out.
Midrange needle just doesnt need to be touch IMHO
ORIGINAL: mmurray70
I did some searching and seems like 90% of people leave it alone as you mentioned. Still wouldnt mind understanding this adjustment better. I found a couple sites explaining how it adjusts the throttle position at which fuel from the high speed circuit is mixed in. Every time you adjust it you also have to adjust the low speed needle the opposite direction to maintain the same low speed mixture.
But I never did find anything about which way to go?
I did some searching and seems like 90% of people leave it alone as you mentioned. Still wouldnt mind understanding this adjustment better. I found a couple sites explaining how it adjusts the throttle position at which fuel from the high speed circuit is mixed in. Every time you adjust it you also have to adjust the low speed needle the opposite direction to maintain the same low speed mixture.
But I never did find anything about which way to go?
lean is in, rich is out.
Midrange needle just doesnt need to be touch IMHO
09-30-2011, 12:56 PM
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RE: Which way is leaner on midrange carb screw??
ORIGINAL: Foxy
On the contrary, the part you bolded is exactly correct. I agree that most people should never touch it, but that bold sentence is gthe most important thing anyone needs to know before messing with it.
ORIGINAL: jmaxey51
not really. you set the LSN first and very seldom touch it again. its usually just tiny adjustments on the HSN, half hour adjustments if that if you are close to tune.
lean is in, rich is out.
Midrange needle just doesnt need to be touch IMHO
ORIGINAL: mmurray70
I did some searching and seems like 90% of people leave it alone as you mentioned. Still wouldnt mind understanding this adjustment better. I found a couple sites explaining how it adjusts the throttle position at which fuel from the high speed circuit is mixed in. Every time you adjust it you also have to adjust the low speed needle the opposite direction to maintain the same low speed mixture.
But I never did find anything about which way to go?
I did some searching and seems like 90% of people leave it alone as you mentioned. Still wouldnt mind understanding this adjustment better. I found a couple sites explaining how it adjusts the throttle position at which fuel from the high speed circuit is mixed in. Every time you adjust it you also have to adjust the low speed needle the opposite direction to maintain the same low speed mixture.
But I never did find anything about which way to go?
lean is in, rich is out.
Midrange needle just doesnt need to be touch IMHO
10-01-2011, 12:56 AM
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RE: Which way is leaner on midrange carb screw??
This is the trick. There is no 'lean' or 'rich' on the midrange adjustment. By adjusting it (and as described making equal and opposite adjustments of the low end at the same time), you are simply changing the position at which the transition from low speed fuel delivery to high speed delivery occurs. It's a very very difficult tuning option to master, I played with it a few times on a few of my race mills, and never found an adjustment that was better than the factory setting. If you want to change it, you should know exactly WHY you want to change it, otherwise you are just messing with something for the sake of it. I must echo the other things you've read and people have said in this thread...don't mess with it. Just don't. Think of it like this...since it doesn't actually directly relate to the amount of fuel delivery, it is not a tuning option that is different from engine to engine (like the low and high speed are). Therefore, the engine maker knows where the optimal position is and sets it for you. This is also why most manufacturers (even top end race mills) don't even provide you with the adjustment.
Here's a nice way to explain the function of all the needles...
Take a pencil and a drinking straw. Hold the straw in your left hand and the pencil in your right. The low speed needle is the pencil and the midrange is the straw. Put the writing end of the pencil into the end of the straw. Now imagine your carb opening, by pulling the pencil out of the straw. This is effectively what your carb does as well as letting air in at the same time of course. So... your low speed needle adjusts how deep the pencil is in the straw when no gas is applied (idle fuel mixture), and the high speed needle controls how much fuel is coming through the straw. Now to imagine the midrange at work, you need to move both your hands simultaneously left or right while maintaining the same amount of pencil insertion into the straw. What this does, is move the gap between pencil and straw left and right (obviously), but without changing the actual gap (hence the need to adjust both needles simultaneously). Now imagine your carb sliding back and forth above this assembly. Hopefully you now have the image in your mind of the carb opening above your straw and pencil. As the carb slides back it reveals the straw and pencil (and the pencil withdraws from the straw at the same rate of course). At some point, the end of the straw is revealed by the opening of the carb. This is when the high speed is considered fully open, and the low end no longer has any effect whatsoever (the pencil having been fully withdrawn). So what you are changing when you adjust the midrange, is the position of the tip of the straw along the carb slide.
Hope that explains why midrange is not a 'rich or lean' adjustment.
Here's a nice way to explain the function of all the needles...
Take a pencil and a drinking straw. Hold the straw in your left hand and the pencil in your right. The low speed needle is the pencil and the midrange is the straw. Put the writing end of the pencil into the end of the straw. Now imagine your carb opening, by pulling the pencil out of the straw. This is effectively what your carb does as well as letting air in at the same time of course. So... your low speed needle adjusts how deep the pencil is in the straw when no gas is applied (idle fuel mixture), and the high speed needle controls how much fuel is coming through the straw. Now to imagine the midrange at work, you need to move both your hands simultaneously left or right while maintaining the same amount of pencil insertion into the straw. What this does, is move the gap between pencil and straw left and right (obviously), but without changing the actual gap (hence the need to adjust both needles simultaneously). Now imagine your carb sliding back and forth above this assembly. Hopefully you now have the image in your mind of the carb opening above your straw and pencil. As the carb slides back it reveals the straw and pencil (and the pencil withdraws from the straw at the same rate of course). At some point, the end of the straw is revealed by the opening of the carb. This is when the high speed is considered fully open, and the low end no longer has any effect whatsoever (the pencil having been fully withdrawn). So what you are changing when you adjust the midrange, is the position of the tip of the straw along the carb slide.
Hope that explains why midrange is not a 'rich or lean' adjustment.
10-01-2011, 03:58 PM
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RE: Which way is leaner on midrange carb screw??
ORIGINAL: Foxy
This is the trick. There is no 'lean' or 'rich' on the midrange adjustment. By adjusting it (and as described making equal and opposite adjustments of the low end at the same time), you are simply changing the position at which the transition from low speed fuel delivery to high speed delivery occurs. It's a very very difficult tuning option to master, I played with it a few times on a few of my race mills, and never found an adjustment that was better than the factory setting. If you want to change it, you should know exactly WHY you want to change it, otherwise you are just messing with something for the sake of it. I must echo the other things you've read and people have said in this thread...don't mess with it. Just don't. Think of it like this...since it doesn't actually directly relate to the amount of fuel delivery, it is not a tuning option that is different from engine to engine (like the low and high speed are). Therefore, the engine maker knows where the optimal position is and sets it for you. This is also why most manufacturers (even top end race mills) don't even provide you with the adjustment.
Here's a nice way to explain the function of all the needles...
Take a pencil and a drinking straw. Hold the straw in your left hand and the pencil in your right. The low speed needle is the pencil and the midrange is the straw. Put the writing end of the pencil into the end of the straw. Now imagine your carb opening, by pulling the pencil out of the straw. This is effectively what your carb does as well as letting air in at the same time of course. So... your low speed needle adjusts how deep the pencil is in the straw when no gas is applied (idle fuel mixture), and the high speed needle controls how much fuel is coming through the straw. Now to imagine the midrange at work, you need to move both your hands simultaneously left or right while maintaining the same amount of pencil insertion into the straw. What this does, is move the gap between pencil and straw left and right (obviously), but without changing the actual gap (hence the need to adjust both needles simultaneously). Now imagine your carb sliding back and forth above this assembly. Hopefully you now have the image in your mind of the carb opening above your straw and pencil. As the carb slides back it reveals the straw and pencil (and the pencil withdraws from the straw at the same rate of course). At some point, the end of the straw is revealed by the opening of the carb. This is when the high speed is considered fully open, and the low end no longer has any effect whatsoever (the pencil having been fully withdrawn). So what you are changing when you adjust the midrange, is the position of the tip of the straw along the carb slide.
Hope that explains why midrange is not a 'rich or lean' adjustment.
This is the trick. There is no 'lean' or 'rich' on the midrange adjustment. By adjusting it (and as described making equal and opposite adjustments of the low end at the same time), you are simply changing the position at which the transition from low speed fuel delivery to high speed delivery occurs. It's a very very difficult tuning option to master, I played with it a few times on a few of my race mills, and never found an adjustment that was better than the factory setting. If you want to change it, you should know exactly WHY you want to change it, otherwise you are just messing with something for the sake of it. I must echo the other things you've read and people have said in this thread...don't mess with it. Just don't. Think of it like this...since it doesn't actually directly relate to the amount of fuel delivery, it is not a tuning option that is different from engine to engine (like the low and high speed are). Therefore, the engine maker knows where the optimal position is and sets it for you. This is also why most manufacturers (even top end race mills) don't even provide you with the adjustment.
Here's a nice way to explain the function of all the needles...
Take a pencil and a drinking straw. Hold the straw in your left hand and the pencil in your right. The low speed needle is the pencil and the midrange is the straw. Put the writing end of the pencil into the end of the straw. Now imagine your carb opening, by pulling the pencil out of the straw. This is effectively what your carb does as well as letting air in at the same time of course. So... your low speed needle adjusts how deep the pencil is in the straw when no gas is applied (idle fuel mixture), and the high speed needle controls how much fuel is coming through the straw. Now to imagine the midrange at work, you need to move both your hands simultaneously left or right while maintaining the same amount of pencil insertion into the straw. What this does, is move the gap between pencil and straw left and right (obviously), but without changing the actual gap (hence the need to adjust both needles simultaneously). Now imagine your carb sliding back and forth above this assembly. Hopefully you now have the image in your mind of the carb opening above your straw and pencil. As the carb slides back it reveals the straw and pencil (and the pencil withdraws from the straw at the same rate of course). At some point, the end of the straw is revealed by the opening of the carb. This is when the high speed is considered fully open, and the low end no longer has any effect whatsoever (the pencil having been fully withdrawn). So what you are changing when you adjust the midrange, is the position of the tip of the straw along the carb slide.
Hope that explains why midrange is not a 'rich or lean' adjustment.
Thanks for the detailed descrition. I actually understood all the concept about "needle and straw" both moving left and right. But to be honest the part im really wondering is... Will my midrange (say 1/3 throttle range) be leaner with the spray bar (straw in your example) deeper into the throttle range or the opposite?
Im guessing deeper right? Since there would be less airflow (which creates low pressure and sucks fuel) over the very tip of the spray bar? Can you confirm?
10-02-2011, 02:37 AM
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RE: Which way is leaner on midrange carb screw??
It won't be leaner or richer, it just changes the timing of the additional fuel delivery from the spray bar. The net effect may be that the mixture is richer at an earlier moment in the throttle opening (before the carb opening completely reveals the tip of the spray bar), but really that's not the purpose. Rather it changes the dynamics of the way the fuel is delivered. Sorry if I went into a bit too much detail, I didn't mean to patronise or condescend, you're obviously not new at this, at least the stuff is there for anyone else reading.
10-02-2011, 03:57 AM
#14
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RE: Which way is leaner on midrange carb screw??
if you move the MSN and don't move the LSN to compensate the mixture will change.....turn the MSN 1/2 turn clockwise and it will lean the tune till you readjust the LSN.......... I use the MSN all the time on my OS engines...it gives you some very fine tuning capability....... if it wasn't meant to be used they wouldn't bother having it there .....
10-03-2011, 07:58 AM
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RE: Which way is leaner on midrange carb screw??
Yah....but you actually know what you're doing bro....
ORIGINAL: supertib
if you move the MSN and don't move the LSN to compensate the mixture will change.....turn the MSN 1/2 turn clockwise and it will lean the tune till you readjust the LSN.......... I use the MSN all the time on my OS engines...it gives you some very fine tuning capability....... if it wasn't meant to be used they wouldn't bother having it there .....
if you move the MSN and don't move the LSN to compensate the mixture will change.....turn the MSN 1/2 turn clockwise and it will lean the tune till you readjust the LSN.......... I use the MSN all the time on my OS engines...it gives you some very fine tuning capability....... if it wasn't meant to be used they wouldn't bother having it there .....
