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Old 06-21-2009, 06:33 AM   #1
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Default Engine Compression.

Hi, I have one STS engine and using heat cycle break-in. Carrently it have ran about a gallon including break-in. So i wish to know when I open up the glow plug and I able to turn the piston a cycle mean this still normal? When I fully tight the glow plug, it hard to turn the piston a cycle. Is this mean pinch is gone and compression is good? Actually pinch or compression is important to make the engine running fine? Currently HSN is 2.5 turn out from close and LSN is 3.5 turn out from close. Please advise and thanks.
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Old 06-21-2009, 07:08 AM   #2
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Sounds like your engine is broke in. You should be good to go, if you have good compression with the plug in place. As for your settings, it's hard to say. Your climate has everything to do with it. If it runs strong, the bottom is crisp, and you have slight smoke coming out you should be good. Temp the engine, to make sure its not running too hot after a few hot laps. You should be good.
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Old 06-21-2009, 07:51 AM   #3
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sounds good, read tuning bible as for needle settings its a great post, ton of good info!
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Old 06-21-2009, 08:15 AM   #4
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Originally Posted by itsshemp View Post
Sounds like your engine is broke in. You should be good to go, if you have good compression with the plug in place. As for your settings, it's hard to say. Your climate has everything to do with it. If it runs strong, the bottom is crisp, and you have slight smoke coming out you should be good. Temp the engine, to make sure its not running too hot after a few hot laps. You should be good.
Hi, the pinch is missing mean is fully broke in? As for smoke, we need to see a lot smoke or slightly during full throttle? I am running Sidewinder 25%. I will check the temp and run between 100-110C with good speed when do tuning. Thanks.

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sounds good, read tuning bible as for needle settings its a great post, ton of good info!
Yeah....and it was great. Thanks.
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Old 06-21-2009, 08:20 AM   #5
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Originally Posted by tkhoo View Post
Hi, the pinch is missing mean is fully broke in? As for smoke, we need to see a lot smoke or slightly during full throttle? I am running Sidewinder 25%. I will check the temp and run between 100-110C with good speed when do tuning. Thanks.
Lack of metal pinch indicates that the engine is fully broken in. Compression is the important thing. If you still have that, you are good to go.

You don't want TONS of smoke, but a good trail of smoke. You don't want it so bad that it's like a cloud of smoke on takeoff. This indicates an overly rich tune.
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Old 06-21-2009, 06:45 PM   #6
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Lack of metal pinch indicates that the engine is fully broken in. Compression is the important thing. If you still have that, you are good to go.

You don't want TONS of smoke, but a good trail of smoke. You don't want it so bad that it's like a cloud of smoke on takeoff. This indicates an overly rich tune.
Great to hear less metal pinch mean fully broken in So if fully broken in, the temp will increased or decrease? My track very dusty, so is hard to see the trail of smoke on driver stand. Look like I need to run and tune at packing lot and minor tune at track....

If I get a cloud of smoke when takeoff mean LSN too rich? Correct me if I am wrong. Thanks to all.
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Old 06-21-2009, 06:56 PM   #7
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You should get a puff of smoke when accelerating hard, it's normal, just make sure it is not too much and you should be good.
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Old 06-21-2009, 08:13 PM   #8
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Great to hear less metal pinch mean fully broken in So if fully broken in, the temp will increased or decrease? My track very dusty, so is hard to see the trail of smoke on driver stand. Look like I need to run and tune at packing lot and minor tune at track....

If I get a cloud of smoke when takeoff mean LSN too rich? Correct me if I am wrong. Thanks to all.
A small puff of smoke and a steady trail through the rpm range is good.

Temp should decrease when it is fully broken in. It deosn't have the friction of the constant grinding against the metal pinch.
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Old 06-21-2009, 09:02 PM   #9
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It sounds like your engine is running in the right temp range, although temp and the amount of smoke coming out of the exhaust are not a good indicator of a good tune. Temps can range from 85° to 160°C, and the only use of watching the amount of smoke is to know if your mixture setting is grossly out of adjustment.

I use the following steps and it results in more precise mixture settings and consistent performance. Start the engine and get it up to temperature. Run the engine at race speed then stop the car in front of you and let the engine idle down for just a couple of seconds. Then, pinch the fuel line and hold it until just before the engine stalls. It should take about 7-8 seconds before the engine is ready to stall. If it takes much less time, then the low-speed setting is too lean. Richen the mixture until the engine can stay running for about 8 seconds - you may need to adjust the idle slightly. If the engine takes much longer than 8 seconds to begin to stall, then the low speed mixture is too rich. This will usually be accompanied by a significant increase in the idle speed just before the engine sounds like it's going to stall. Lean the low-speed mixture until the engine is able to idle for just 7 to 8 seconds. You'll probably have to lower the idle speed.

Once you have the low-speed needle dialed in, focus on the high-speed needle. run the car again at full speed, then bring it in and let it idle in front of you. If the idle comes in very low then gradually raises back to a normal speed, your high-speed needle is a little rich. It dumps excess fuel into the engine, and it causes the idle to drop when you release the throttle after a high-speed pass. Conversely, if the engine stays at a high idle for a few seconds and then settles down to a normal speed, then the high-speed needle is too lean. After a high-speed pass, if it's too lean, there's not enough fuel going through the engine, and the engine will tend to run on. The proper low-speed needle setting helps to return the idle to normal once the engine has had time to idle for a little while.

The final test should be done at full running temperature. Stop the car in front of you, then apply full throttle. There should be no hesitation and the engine should pull strongly right up to maximum RPM. If the low speed is still slightly lean, the engine will appear to cut off for a second, then accelerate suddenly. If it's a little too rich, the engine will accelerate more smoothly, but not as strong as it should. Adjust accordingly. If the high speed needle is too rich, the engine will appear to labor in the mid range during acceleration. It might possibly clean out at the high-end if the mixture setting isn't too bad. If the high-speed is too lean, then the engine will flat stop accelerating at the higher rpm range. The exhaust note will sound "dry" if that makes sense, and the engine will only begin to run normal once you back off the throttle.

These are all signs that you can use to determine whether your engine is running properly, and they'll result in a much better mixture setting than if you tune by the amount of smoke or the engine temperature. Both of these indicators tell you of if you're WAY OFF on the mixture setting, and are useful in that respect, but I don't fine tune an engine based on either one. The feel and sound of the engine tell me must more than the amount of smoke or the engine temperature.

Hope this helps.
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Old 06-22-2009, 01:44 AM   #10
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Hi SteveP, thanks for your time for the long advise. Would like to know when pinch the fuel line to check LSN, i need to pinch ~1 inch from the carb? And I not understand on below in red font, can you advise on this. Thanks in advance.

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It sounds like your engine is running in the right temp range, although temp and the amount of smoke coming out of the exhaust are not a good indicator of a good tune. Temps can range from 85° to 160°C, and the only use of watching the amount of smoke is to know if your mixture setting is grossly out of adjustment.

I use the following steps and it results in more precise mixture settings and consistent performance. Start the engine and get it up to temperature. Run the engine at race speed then stop the car in front of you and let the engine idle down for just a couple of seconds. Then, pinch the fuel line and hold it until just before the engine stalls. It should take about 7-8 seconds before the engine is ready to stall. If it takes much less time, then the low-speed setting is too lean. Richen the mixture until the engine can stay running for about 8 seconds - you may need to adjust the idle slightly. If the engine takes much longer than 8 seconds to begin to stall, then the low speed mixture is too rich. This will usually be accompanied by a significant increase in the idle speed just before the engine sounds like it's going to stall. Lean the low-speed mixture until the engine is able to idle for just 7 to 8 seconds. You'll probably have to lower the idle speed.

Once you have the low-speed needle dialed in, focus on the high-speed needle. run the car again at full speed, then bring it in and let it idle in front of you. If the idle comes in very low then gradually raises back to a normal speed, your high-speed needle is a little rich. It dumps excess fuel into the engine, and it causes the idle to drop when you release the throttle after a high-speed pass. Conversely, if the engine stays at a high idle for a few seconds and then settles down to a normal speed, then the high-speed needle is too lean. After a high-speed pass, if it's too lean, there's not enough fuel going through the engine, and the engine will tend to run on. The proper low-speed needle setting helps to return the idle to normal once the engine has had time to idle for a little while.
The final test should be done at full running temperature. Stop the car in front of you, then apply full throttle. There should be no hesitation and the engine should pull strongly right up to maximum RPM. If the low speed is still slightly lean, the engine will appear to cut off for a second, then accelerate suddenly. If it's a little too rich, the engine will accelerate more smoothly, but not as strong as it should. Adjust accordingly. If the high speed needle is too rich, the engine will appear to labor in the mid range during acceleration. It might possibly clean out at the high-end if the mixture setting isn't too bad. If the high-speed is too lean, then the engine will flat stop accelerating at the higher rpm range. The exhaust note will sound "dry" if that makes sense, and the engine will only begin to run normal once you back off the throttle.

These are all signs that you can use to determine whether your engine is running properly, and they'll result in a much better mixture setting than if you tune by the amount of smoke or the engine temperature. Both of these indicators tell you of if you're WAY OFF on the mixture setting, and are useful in that respect, but I don't fine tune an engine based on either one. The feel and sound of the engine tell me must more than the amount of smoke or the engine temperature.

Hope this helps.
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Old 06-23-2009, 11:48 PM   #11
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tkhoo - You are welcome for the advice. It doesn't matter where you pinch the fuel line - the result will be the same.

The area highlight in red - possibly a better (easier) way to say this...

What I'm trying to say is, when the high speed needle is too lean, the engine will have the following behavior after a high-speed pass: engine rpm tends to stay high for a few seconds, but the engine will eventually return to a normal idle when the low-speed mixture is correct. So, if your engine won't idle when you let off the throttle, but eventually returns to idle, then it's possible that you have a lean main needle and a properly set low-speed needle.
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Old 06-24-2009, 12:24 AM   #12
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Steve

great post, thanks for sharing the knowledge.

Can you please elaborate on the pinch method? how far away from the carb should you pinch so that the 7-8s method makes sense? At idle, an extra inch of fuel pipe can mean a couple of seconds.

thanks
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Old 06-24-2009, 08:11 AM   #13
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Steve

great post, thanks for sharing the knowledge.

Can you please elaborate on the pinch method? how far away from the carb should you pinch so that the 7-8s method makes sense? At idle, an extra inch of fuel pipe can mean a couple of seconds.

thanks
Paul
Hi lonestar, sorry to jump in,
The distance won't matter as long as you pinch real hard and block the fuel passage completely.
Meaning it will only consume the fuel inside the crankcase at that moment.
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Old 06-24-2009, 12:39 PM   #14
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Hi Lonestar,

As I mentioned in my previous post, and as suggested by orangbaligila, it doesn't matter where you pinch the fuel line - it simply stops the fuel flow. Think of it this way: put a straw in a glass of water, then plug the top of the straw with your finger. If you raise the straw out of the water, none of the water escapes until you remove your finger. Next, pinch the straw half way down, and do the same thing. The end of the story is that you get the same result. The fuel flow will stop the moment you pinch the fuel line, no matter where you pinch it.
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Old 06-24-2009, 12:50 PM   #15
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Quote:
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Hi Lonestar,

As I mentioned in my previous post, and as suggested by orangbaligila, it doesn't matter where you pinch the fuel line - it simply stops the fuel flow. Think of it this way: put a straw in a glass of water, then plug the top of the straw with your finger. If you raise the straw out of the water, none of the water escapes until you remove your finger. Next, pinch the straw half way down, and do the same thing. The end of the story is that you get the same result. The fuel flow will stop the moment you pinch the fuel line, no matter where you pinch it.
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