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O.S. 21TM running hot?

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Old 03-23-2014, 09:23 AM
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rcagpilot83
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Default O.S. 21TM running hot?

In the process of tuning a 21tm, I started off with a rich setting then slowly started leaning it out. I noticed that by the time I got it to where it was running like it should my temps were between 320-330 on WOT runs. To me that seems a bit warm lol. But I still had a good smoke and I have heard guys say as long as you have good smoke don't worry about the temps. Im using O'Donnell R2R T blend 33% nitro 12%oil, LC3 plug the motor came with, THS Racing dual chamber pipe.
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Old 03-23-2014, 10:14 AM
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It should not be that hot...is your tool wonky or is it where you are aiming it? I presume the engine has been broken in?

Also you say "I started off with a rich setting then slowly started leaning it out"...are you only adjusting the HSN?
The HSN should be adjusted with high RPM wide open throttle runs.
The LSN should be adjusted with stand/go tests.
Always adjust HSN first....and only try to tune a warm engine.
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Old 03-24-2014, 09:30 AM
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You ONLY tune an engine when at Operating Temperature. Main needle/HSN *first* and idle/midrange mixture *second* to get a fast throttle transition from idle to WOT. Indeed set the main needle/HSN with WOT runs until it cuts out or the RPM sags then back off 1/8th turn rich. If you're getting that hot on a WOT run you're on the edge of too-lean if it isn't cutting out. However, Do NOT rely on the temp gun to tune your engine. They are prone to inaccurate readings. It's always best to tune by ear. Forget smoke trails as a tuning aid at first as not all fuels smoke the same when burned. Also the glow plug heat range can affect the smoke amount. I will say the smoke color typically will be grey if lean and blue if rich. If the idle hangs after a WOT run for a short time, the idle mixture is too rich and the idle gap too wide. This can cause (and often does) all sorts of tuning problems.

Last edited by 1QwkSport2.5r; 03-24-2014 at 09:33 AM.
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Old 03-25-2014, 03:15 AM
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rcagpilot83
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had it out after work yesterday, noticed my idle was hanging a bit so I lowered idle and leaned the lsn a bit. It is a bit better but still got to between 300-320. Seems if I tune it so it runs around 240-270 it runs like crap. I did see someone make the comment that a 21 motor with 25 or 30% fuel shouldn't need a hot plug and suggested trying a LC4 or a #8.
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Old 03-25-2014, 07:07 AM
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I use hot plugs with 30% nitro all the time. The only time I see my engine getting close to 300F is if I run in a good bit of tall grass. Now my engines are all broke in well. If your engine isn't broke in real well yet, it will run a bit warmer. If it's still pretty new, run it a bit richer and give it some run time. Tighter engines tend to be a little finikier until they get some time on them before they "behave". If the engine is broke in good, tune it so it's running slightly rich on top with a good clean transition to WOT and let 'er buck. If the engine truly overheats, it's gonna just quit. You'll see smoke from the engine before then though.
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Old 03-25-2014, 11:29 AM
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Yeah the motor is new, I have little less than a gallon through it.
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Old 03-25-2014, 12:15 PM
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Quote:
Originally Posted by rcagpilot83 View Post
Yeah the motor is new, I have little less than a gallon through it.
That alone will contribute to it running warm. Just run it richer and give it time. Don't be too concerned about it unless you see smoke coming off the engine.
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Old 03-25-2014, 02:11 PM
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Yup, think that's it. Ran 3 tanks this evening and by the 3rd it barely hit 300 and was running pretty good too.
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