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Old 03-28-2010, 03:03 AM   #1
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Default LSN Problem

I am having a heck of a time setting the lsn Ive got the engine up to warming up stage far as putting it on the ground and letting it warm up to roughly 250-280 range when it gets to the 280 range I richen it up to it starts holding a stable temp around 250-260 and is running good and stable and also the air temp was in the 60's to mid 60's. When i went to do the pinch test around 1 inch to 1.5 inch it took it 5 seconds to shut off didnt pick up idle or nothing just killed the motor. if i lean I die out during a run if I richen up I die out at the setting im at right now im getting roughley 20 to 25 min a tank on a 1/8th scale comp buggy. I fill that my low end is not picking up as well as it should It ran great today realy no issues other then according to the pinch test my lsn is wrong also I tried that other method of riching it up till it dies out then turning back half of where it died out I may have done that one wrong but the pinch test I am sure of. I am also running a JP-3 pipe and Byrons 30% nitro 11% lub. Im pretty sure I have 2 shims also. So by saying this could someone please give me some solid fact about the lsn as in to what to expect and exact tune of the lsn. Also far as the idle screw the carb is setting a lil more or less then a 1/16th open
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Old 03-28-2010, 07:01 AM   #2
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20-25 minutes a tank? you're way lean!!!

what motor?

no really, the pinch test:

-at temp (over 200) and with smoke the whole straight.

- i do it at 1 inch with pliers and let the idle drop to rest idle. pinch and count to 4. if the motor is still running at 4 its on the rich side, lean 1 hour per second over 4 and try again.

-if you count to 4 and its dead, richen 1/4 turn and start over. once it quits right at 4 set the gap screw so the idle holds for about 10 seconds before it drops to rest.

do this whenever you change fuel or after you have changed the lsn chasing a tune after a bad plug. once the lsn is set to your fuel, you only need to adjust the gap screw for weather changes. also set hsn to straight away length so its good smoke (at temp, usually 3 laps or so) the whole straight. at the end of the tank as the tune leans a bit you may be no smoke at the end of the straight but temps will stay very consistent. been doing it this way a while now with good results, good run times, long plug life, temps in the 230's (small-mid tracks) and good engine life.




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Old 03-28-2010, 11:22 AM   #3
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I thought when tunning the LSN you wanted the idel to come to rest as soon as you let off the throttle. If it takes 10 seconds then I thought that meant that the LSN was rich. IDK I may be wrong. Any other thoughts out there?
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Old 03-28-2010, 01:27 PM   #4
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If your running those temps that motor is going to have a very short life. You shoud never run over 260 and that is a perfect race tune. You want to be in the 210 to 230 range. If your running that hot you are way to lean on the top end. Both needles flush and idle gap set .5 to no more than 1 mm. Start from there. Set yor idle with the low speed and once you have a good idle start leaning the top. As you lean the top your idle will probably go up so then you have to fatten the bottom. All your adjustments should be an hour or two at a time. What motor are you tuning anyway?
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Old 03-28-2010, 01:31 PM   #5
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If your running those temps that motor is going to have a very short life. You shoud never run over 260 and that is a perfect race tune. You want to be in the 210 to 230 range. If your running that hot you are way to lean on the top end. Both needles flush and idle gap set .5 to no more than 1 mm. Start from there. Set yor idle with the low speed and once you have a good idle start leaning the top. As you lean the top your idle will probably go up so then you have to fatten the bottom. All your adjustments should be an hour or two at a time. What motor are you tuning anyway?
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Old 03-28-2010, 01:36 PM   #6
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I thought when tunning the LSN you wanted the idel to come to rest as soon as you let off the throttle. If it takes 10 seconds then I thought that meant that the LSN was rich. IDK I may be wrong. Any other thoughts out there?
yes but after 10 seconds it drops to a lower gurgly 4 stroke idle then quits.
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Old 03-28-2010, 01:41 PM   #7
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yes but after 10 seconds it drops to a lower gurgly 4 stroke idle then quits.
Not if its tuned right. If its tuned right it will drop right down to idle and idle all day long. If yours is doing that your lean on top and fat on the bottom. Fatten the top a couple of hours lean the bottom a couple of hours and see what happens.....
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Old 03-28-2010, 02:34 PM   #8
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Not if its tuned right. If its tuned right it will drop right down to idle and idle all day long. If yours is doing that your lean on top and fat on the bottom. Fatten the top a couple of hours lean the bottom a couple of hours and see what happens.....
That's what I thought. Mine while drop to idel as soon as I let off the throttle and set there and idel for ever. So does that mean my motor is tuned right? I have been doing this for about 3 yrs and still have trouble tunning but I think I'm starting to get the hang of it.
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Old 03-28-2010, 02:40 PM   #9
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That's what I thought. Mine while drop to idel as soon as I let off the throttle and set there and idel for ever. So does that mean my motor is tuned right? I have been doing this for about 3 yrs and still have trouble tunning but I think I'm starting to get the hang of it.
Yes you have it right. After you have the air gap and LSN set right the only thing you should ever have to readjust to temp conditions and etc is the HSN.
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Old 03-28-2010, 02:43 PM   #10
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yes but after 10 seconds it drops to a lower gurgly 4 stroke idle then quits.
The gurgly sound you get after 10 secs is the case loading up and thats why it dies.
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Old 03-28-2010, 03:16 PM   #11
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If you are seriously getting 20-25 mins a tank then either you are waaaaayyyyy too lean or you are just putting around. You're tuning methods are wack. Sorry but they are. When you tune start from the rich side. Run it until you get to about half a tank then start to lean the high speed needle until it cuts out or you get no more performance increase. Make sure that you have plenty of smoke. If it cuts out or there isn't much of a smoke trial then richen it back up 1 hr. Then tune your lsn with the pinch test. A properly tuned motor when brought in to a stop should have a slight high idle for a second or two then drop down to a lower idle. When it drops that is when you want to do your pich test. And no it shouldn't idle all day if it does it's too lean. You want it to sit and idle, but not more than about 30 secs. After you have the lsn in the ball park with the pinch test you can do a punch test. Do a wot pass and bring it in to a stop. Count ten seconds and punch it. It should have strong acceleration, and a good smoke trail without any hesitation. Make very small changes to the lsn as it is really easy to get it way off. Good luck.
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Old 03-28-2010, 06:18 PM   #12
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I fill that my low end is not picking up as well as it should
also check your clutch and/or gearing. more traction will make the car boggy compared to loose traction. driving on grass vs dusty clay.
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Old 03-28-2010, 06:35 PM   #13
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If you are seriously getting 20-25 mins a tank then either you are waaaaayyyyy too lean or you are just putting around. You're tuning methods are wack. Sorry but they are. When you tune start from the rich side. Run it until you get to about half a tank then start to lean the high speed needle until it cuts out or you get no more performance increase. Make sure that you have plenty of smoke. If it cuts out or there isn't much of a smoke trial then richen it back up 1 hr. Then tune your lsn with the pinch test. A properly tuned motor when brought in to a stop should have a slight high idle for a second or two then drop down to a lower idle. When it drops that is when you want to do your pich test. And no it shouldn't idle all day if it does it's too lean. You want it to sit and idle, but not more than about 30 secs. After you have the lsn in the ball park with the pinch test you can do a punch test. Do a wot pass and bring it in to a stop. Count ten seconds and punch it. It should have strong acceleration, and a good smoke trail without any hesitation. Make very small changes to the lsn as it is really easy to get it way off. Good luck.
Mine will idle all day and in race conditions run 230 all day long, to lean? If anything im still running fat. Your pros run at 260 and there motors all will idle all day long. The high Idle you have before it drops to a lower idle is because of a fat condition not a lean one. Its loaded up with fuel so it has to burn it off before it will go to normal idle. But to each his own.
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Old 03-28-2010, 07:26 PM   #14
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Mine will idle all day and in race conditions run 230 all day long, to lean? If anything im still running fat. Your pros run at 260 and there motors all will idle all day long. The high Idle you have before it drops to a lower idle is because of a fat condition not a lean one. Its loaded up with fuel so it has to burn it off before it will go to normal idle. But to each his own.
http://www.rchobbies.org/cars_eng-tuning.htm

Scroll down to the lsn section.

You are wrong, if you have just come off of full throttle then the majority of the fuel is burned and after a few seconds the crankcase loads back up with fuel and brings the idle down. If your theory is true then why does a lean lsn cause a high idle, and why does your idle speed up when the fuel tank runs dry?
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Old 03-28-2010, 08:01 PM   #15
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http://www.rchobbies.org/cars_eng-tuning.htm

Scroll down to the lsn section.

You are wrong, if you have just come off of full throttle then the majority of the fuel is burned and after a few seconds the crankcase loads back up with fuel and brings the idle down. If your theory is true then why does a lean lsn cause a high idle, and why does your idle speed up when the fuel tank runs dry?
How many motors have you tuned? Anybody can read but real world is different. Why does a lean lsn cause a high idle? Because your to lean. You either fatten it up or close your idle screw up some. When your wide open throttle your loading the case to maximum capacity of fuel. When you let of the throttle the case is still full. How do you stop this from happening to have a nice even idle. Simple you lean things out. Before you tell sombody there wrong tune some motors and get some real world experience.......
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