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Performance tuning, let the engine tell you.

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Unread 12-05-2009, 2:56 PM   #1
Extreme RC Mods
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Performance tuning, let the engine tell you.

This is the way that I tune engines, there are many other ways to tune but I figured this is the most simple way to do it so I will share my info. This technique is for a fully broken in engine that is ready for a full performance tune. This tuning procedure will set your needles where they need to be for optimum performance, there is no guessing, the engine will tell you.

For this to work the engine has to be at running temps (or as close to it as possible) as well as having the standard 1mm gap for the carb opening.

#1) High Speed Needle.
Pull a wot pass a couple times and listen what the engine does when you let off the throttle. As long as the rpm drops right to idle, the HSN is either good or on the rich side. At this point you can lean the HSN in 1/12 increments until the idle seems to hang a little after a wot pass, when it starts to idle high after a pass it is just on the lean side of a perfect tune. Back the HSN out 1/12 turn at a time after a wot pass until the engine drops right to idle after a pass. Now your HSN is set.

To give an explanation to what is happening is simple. If your HSN is too lean, after a wot pass when you let off the throttle the engine is still lean causing the idle to hang and idle high until the LSN has a chance to take over and meter the right amount of fuel to bring the idle down to normal running speed (given the LSN is set correctly)

Now if the opposite happens, after a wot pass when you let off the throttle, if it drops to a good idle right away and then starts to idle back up too high, this is a sign that the LSN is too lean. If it comes off wot with a good tune and will drop rpm nicely then the HSN is metering the fuel properly but once it hits idle the LSN being too lean will quickly take over causing the rpm to go back up.

#2) Low Speed Needle
Most of this setting was explained above but there are a few little tricks you can use to make sure the LSN is adjusted perfectly. We all know that you don't tune for temps but a temp gun is very handy for this part. After some wot passes with the engine good and warm, bring it in and let it sit for about 10 seconds. At this point take your temp gauge and hold it as steady as possible on the head, what you want to see is the temp dropping a degree every 4-5 seconds. You want the temp to drop very slightly at idle because when your off throttle the engine should be cooling, if not, the temps will keep pushing higher with on and off throttle running and will cause temp issues.



This is how I do it and I have tuned a lot of engines for people whether bashing or racing. I have seen across the board from beginners to veterans that when they hear the high idle after a pull, the first thing they go for is the LSN when in fact it is the HSN causing the issue. I hope it's not too hard to understand as typing it out is much harder then explaining it to someone first hand, if you have any questions feel free to ask.

Robin.
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Last edited by Extreme RC Mods; 12-05-2009 at 2:58 PM.
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Unread 12-05-2009, 7:13 PM   #2
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Will have to make an effort to try your methods the next time I run. I get a weird tune with my LRP's depending on the pipe and fuel tank I'm running. It's weird... on my aftershock with an LST2 pipe and 150cc tank, it will tune great. No hanging after WOT, solid idle that will sit for at least 20-30 seconds without loading up. I still get an occasional mid throttle rich condition though. I had an HPI polished savage pipe for a while, but had a horrible mid-range rich problem. If I was able to tune it out, it was way too lean on WOT and idle was erratic (assuming lean on LSN as well). After switching to the LST2 pipe which is more restrictive, it cut my mid-range problem almost completely.

Running an HPI header with an LST2 pipe (figured it worked so well on the aftershock, I bought one as soon as I got an LRP for my savage) and 125 cc buggy tank on my savage and the tune is just all over the place. Doesn't idle right, runs on the warm side, if I get it to drop to idle ok, it's too rich on the WOT run. I switched out the header for one that has two bends instead of the tight HPI bend and that helped. I also changed out the tank for a truggy 150cc tank and that helped more. Then I switched to a less restrictive pipe (hot bodies savage pipe I think) and now it will tune almost as well as my LRP on the aftershock.

You'd think... after 8 years of running nitro, this would be a breeze!
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Unread 12-05-2009, 9:55 PM   #3
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Very well explained. I'd like to add that once you set the engine as per above, it should never need massive changes. Before you go to twisting needles, check for leaks and glow plug condition. I have screwed up a perfectly good tune when many a time all I needed was a new plug or header gasket or both.
Anytime a glow plug becomes distorted from either an overlean condition or excess compression( Trying to run an engine not broke-in fully wide asss open) You need to toss the plug. It will not run right. Just because it still glows bright does not mean it's good.
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Unread 12-05-2009, 11:47 PM   #4
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Originally Posted by olds97_lss View Post
You'd think... after 8 years of running nitro, this would be a breeze!
No kidding Olds...I have been doing nitro for six years and still get frustrated and stumped sometimes. I have days that I can't get any nitros to run correctly. I have to say hell with it and break out the Baja. I was thinking about trying this as well. I kinda use something like this already but this is a lot better explained. Kinda like the LRP .30 I have in my Savage that I could not get to run for crap. Put a JP-3 pipe on it and all it's problems cleared up. Now it is an animal. Puts my 16lbs Savage on it lid quick.
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Unread 12-18-2009, 8:49 AM   #5
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Back to the top, a lot of you new nitro owners need to read this.....it's gospel!
Edit; Joey, what other pipes have you tried? I think a JP-3 would choke a .30..It's a little too restrictive for good .28's.
The JP-3 is mainly for .21's that need help on bottom end.
My LRP .28 loved the JP-2, made it scream and still had violent bottom end.

Last edited by Scrogg; 12-18-2009 at 8:53 AM.
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Unread 12-18-2009, 9:39 AM   #6
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my LRP's sometimes cause me headaches as well but it is usually me trying to run them when it is cold out... btw thanks for simplifying it down for us:-)

Last edited by syphon68; 12-18-2009 at 9:42 AM.
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Unread 12-18-2009, 2:05 PM   #7
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Just for reference, my LRP took 1 & 3/4 gallons to fully break in. After that, it tuned very predictable. It's an engine that hardly needs the HSN touched, but the LSN needs leaned a lot.
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Unread 1-07-2010, 1:33 AM   #8
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tuning

I read your post multiple times.
here is the thing, when I bought my truggie from the dealer, the repair fixer chap, who apparently knows his stuff..... ran the engine in for me and set the carb....

And of coarse this is my first nitro car, been a big electric fan before.
so I don't really know what to do.
the engine is slugish, when you pull the trigger, have to rev the car a little to get her going.

And of coarse I don't know much about tuning an engine, there are lots of screws and do they go clockwise or anti clockwise, and which one is which???

I apologise for the stupidity, I don't want to destroy an engine...
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Unread 1-07-2010, 9:27 AM   #9
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There are no stupid questions, nobody was born knowing RC Nitro lol.
Here is a picture I took with all the needles labeled, it should help you understand which needles to play with when tuning. As for which way to turn the needle, think of a garden hose, Counter clock wise will give you more water flow, clockwise will restrict or shut off the water, it's the same concept.

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Unread 1-07-2010, 1:58 PM   #10
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Fantastic explanation.
I have a question concerning the relationship in a three needle set-up between the LSN and the MSN.
Years ago I was told that these two should be moved in unison.
For example, if the LSN gets turned in an 1/8th, then the MSN would be turned out an 1/8th (or vice versa).
Seems to make sense, but then I could rationalize why that might not be the case...
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Unread 1-07-2010, 7:39 PM   #11
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I always read that on engines with a MSN.....DON'T MESS WITH IT. lol It's far too easy to mess up a tune with the MSN that's it just not worth it unless you REALLY know Nitro tuning like the back of your hand.
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Unread 1-07-2010, 10:37 PM   #12
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Originally Posted by TGL View Post
Fantastic explanation.
I have a question concerning the relationship in a three needle set-up between the LSN and the MSN.
Years ago I was told that these two should be moved in unison.
For example, if the LSN gets turned in an 1/8th, then the MSN would be turned out an 1/8th (or vice versa).
Seems to make sense, but then I could rationalize why that might not be the case...

You are correct to a point, if you were to adjust the MSN, the LSN would have to be adjusted as well to match, they do work in unison. The adjustments would not be equal as the LSN has a much finer thread the the MSN will have. The MSN sets where the spray bar is, in the carb, most of the time it is set from factory to operate most efficiently with the engine and does not require tuning. Unless you are a master at tuning and understand every aspect of the carb and also know why you are adjusting it, I would leave the MSN alone, most attempts will end in an engine running worse then when you started.
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Unread 1-08-2010, 2:39 AM   #13
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brilliant, thank you very much. it does make a lot of sense now, just wish it would stop raining......what about the idle gap screw, should I just leave it be.
I never realized how sensitive the LSN and HSN needles are wow......
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Unread 1-08-2010, 9:30 AM   #14
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The idle gap screw should be set to hold the barrel of the carb open from .5mm to a maximum of 1mm. After this screw is set don't mess with it, tune around it so the engine idles and launches nicely. Some will say to run a much bigger gap, doing this will only cover other potential tuning issues especially the hanging high idle after a WOT run, even if the HSN is set correctly.
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Unread 2-08-2010, 6:20 PM   #15
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aftershock

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Originally Posted by Scrogg View Post
Very well explained. I'd like to add that once you set the engine as per above, it should never need massive changes. Before you go to twisting needles, check for leaks and glow plug condition. I have screwed up a perfectly good tune when many a time all I needed was a new plug or header gasket or both.
Anytime a glow plug becomes distorted from either an overlean condition or excess compression( Trying to run an engine not broke-in fully wide asss open) You need to toss the plug. It will not run right. Just because it still glows bright does not mean it's good.
hey I have a losi aftershock, and I want to upgrade its performance. any sugestions?
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