Performance tuning, let the engine tell you.

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Grumpy1822 said:
Yep, I ve seen Robin helping people on forums for years now. Hes goten kicked in the teeth for his efforts several times too. He shrugs it off and maintains a good attitude. I'm proud to call him my freind.
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I'm guilty of this, but it isn't something I'm proud of.
 
Thanks for the tips Robin. I think I am going to factory reset my engine and try this to see if I can get the most out of it.
 
Thanks Robin, I'm giving this a try right now!

One question:

Purenitro said:
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.
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When I did this my temps keep rising @ idle. . . do I need to richen up the LSN?
 
Yes, it should not be gaining temp at idle, you should richen it up some until it slightly drops at idle.
 
Ok got my idle to drop its temp @ 1-2degrees every 5 secs.

But when I pull WOT, it still revs high for a few seconds-or until it hit the brakes. . .which from what I read in the first post would be on the lean side---BUT there is still lots of(at least in my opinion) blue smoke at WOT, and at idle it lightly spits my hand under the exhaust.
 
If it's dropping to idle like it should (with the brakes applied) chances are the carb is not closing all the way on it's own. The end points have to be set and the carb has to close fully on it's own for this to work, if the carb is not closing then it's not going to drop like it should.
 
Oh ok, so would/could this be a spring issue? The truck is basically still new, btw.
 
Javage said:
Oh ok, so would/could this be a spring issue? The truck is basically still new, btw.
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Not quite sure why the carb won't close on it's own unless maybe the trim is set to hold it open just a bit and hitting the brakes closes it that much further, I think that may be the problem. There is also some play in the stock linkage that may be playing a small roll in this as well. As for the fluid coming out of the pipe, that is normal, the lube in the fuel isn't supposed to burn completely. A perfectly tuned engine will still have lube coming out of the pipe as that's what leaves the mess all over the side of the truck.
 
Purenitro said:
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, a temp gun is not required (other then high temp safety check) because 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. The veterans are surprised when we richen the HSN an hour or two and the problem goes away. 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, or shoot me a pm with your number and we can talk more in depth about it (Canada and USA only)

Robin.
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Great info.
 
Purenitro said:
Not quite sure why the carb won't close on it's own unless maybe the trim is set to hold it open just a bit and hitting the brakes closes it that much further, I think that may be the problem. There is also some play in the stock linkage that may be playing a small roll in this as well. As for the fluid coming out of the pipe, that is normal, the lube in the fuel isn't supposed to burn completely. A perfectly tuned engine will still have lube coming out of the pipe as that's what leaves the mess all over the side of the truck.
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Ya sometime to get it to idle right I have to close the carb back which leaves smaller than 1mm when closed. But I usually have it set so that at full brake it doesn't close the throttle any.
 
This is one of the best threads:mug:.With video it will be perfect.
 
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I know this question might be stupid but..

Yust one question do you change idle needle settings after/between tunning or yust 1mm gap and that it is it?
 
get the truck started .... then with the wheels off the ground ... adjust idle screw so the engine runs nice and smooth but the wheels don't turn ... then your good...if the truck starts picking up rpm as your tuning its the lsn being to lean or the hsn to lean.. get the truck tuned then back the idle down a tad till tires arent spinning again...
 
unicorn87 said:
I know this question might be stupid but..

Yust one question do you change idle needle settings after/between tunning or yust 1mm gap and that it is it?
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All tuning should be done when the engine is warm and right after some wot passes, the idle should be set after you get the HSN dialed in. If the engine idles back up after you let off the throttle then you can richen it up some to stop this but don't worry too much about the lsn until the top end tuning is done.
 
I got my XL back and I'm gonna tune using this method. I ran a half tank through it and noticed it was hanging before settling to idle and it was a little hard to start and sluggish on the bottom. I'm thinking a bit lean on the high side and a bit rich on the low side. My temps got to about 250-260 so if I richen the top end a bit I might get some nice cool temps out of it. Thanks for the info. I started like you Robin. Not many people around me into it and I don't know anyone with RC's period let alone nitros. I got a Super Nitro RS4 about 6 years ago and now the XL but I don't have anybody to learn from so this site is like a godsend LOL.
 
Ya a vid of the idle droping from WOT would be great. My idle hangs on for about 10 to 15 seconds after WOT runs. HSN is a tad on the rich side and my LSN is also. As a matter of fact I think I turned that LSN only about 1/16th of a turn or so. She starts up and idles fine a little high but idles. Once temps are around 220 to 240 she rips. I have noticed alot of blue smoke throughout the RPM range. Seems to lag a little during punch an doesnt seem to have all that amazing top speed until she is up to temp. Might have to adjust my shift points in my tranny also. I was thinking about leaning the HSN just a hair then the LSN then adjusting my idle. Kinda runs OK the way it is and I guess I'm being a little bit of a meow meow about screwing with it.
 
WJC said:
Ya a vid of the idle droping from WOT would be great. My idle hangs on for about 10 to 15 seconds after WOT runs. HSN is a tad on the rich side and my LSN is also. As a matter of fact I think I turned that LSN only about 1/16th of a turn or so. She starts up and idles fine a little high but idles. Once temps are around 220 to 240 she rips. I have noticed alot of blue smoke throughout the RPM range. Seems to lag a little during punch an doesnt seem to have all that amazing top speed until she is up to temp. Might have to adjust my shift points in my tranny also. I was thinking about leaning the HSN just a hair then the LSN then adjusting my idle. Kinda runs OK the way it is and I guess I'm being a little bit of a meow meow about screwing with it.
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ya my f 4.1 engine has always done this and could never figure out why when ever you let off the throttle it still idles high for a few seconds then settles down....
 
It doesnt seem to bother anything but I'd still like the idle to come down a little bit faster. Also once shes up to temp (K 4.6 ) she runs better on the grass then on the pavement. I mean I get way more response on a slightly grassy area then on road. I neeed a track to go to, I wish I had the space I'd build one myself.
 
On second thought I might just try to richen up my HSN. She just runs a little on the slow side off the line and bogs down until I can get her warmed up. I know that the bogging is due to the HSN not being set right
 
I have a axial spec 1 .28 motor, during a cleanup/teardown i had pulled the high speed needle from carb (not running) and put it back immediately. Ran fine before, now i have fuel pouring out the exh. and will not idle. I think maybe i have an air leak, noticed bubbles in fuel line after installing a new fuel filter. any help would be appreciated, thanks in advance.
 
Could be too rich, maybe try and lean it out some.
 
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