Argess

Below, is a cut'n'paste of part of Mr. Paris's tuning recommendations. I don't do it that way. In fact, I don't know anyone who does. The end result of his method would be to have an exactly tuned idle which is impossible to maintain. It would either eventually lean out and die, or it would eventually get rich and the rpm drop....and then die as he wants the idle stop screw adjusted for the high (2-stroke idle). I don't think his tuned engines would pass the "pinch test" either. BUT, the late Mr. Ron Paris is heralded as the best engine guru ever,....which I don't doubt. Would some of you "other tuners" please comment on his method. Thank-you.

From Mr. Paris's Engine Tuning Tech Tips:

Carburetor Needle balance:
It has come to our attention some racers are making the mistake of setting the idle speed opening to wide [high idle] and setting the bottom end too rich!
This will give a false normal idle speed even though the speed is set to high because it “loads up� the engine with excess fuel causing the idle to be lower than set!
The end result is a very unstable idling engine that surges and may cut out as full throttle is applied because the over rich bottom end can disguise a too lean TOP end setting!!!
Let’s address this a little more in depth!
Idle speed opining set too wide:
It is possible too set the idle screw adjustment in to far but yet the idle speed is not high!
Even though the air regulation [carb barrel or slide] may be set to a position that would normally equal a vary fast idle, the idle is low because the low speed mixture adjustment is set so rich that the engine loads up with excess fuel and the engine goes into what’s commonly called a four cycle idle.
One tell tail sign of this is if after reving up the completely warmed up engine it tends to idle fast for a few seconds then drops to lower idle speed.
[Here we go again with the written sound effects :-)]
Something like da..da..da..da..da..da..da..da then it drops to da….da….da….da [if it were sheet music it would be like dropping from 8 beats per measure to 4 beats per measure]
If you start leaning the bottom end a little at a time [then repeat the reving up and idle test] and it takes longer before the idle drops your going in the right direction!
Eventually as you keep leaning the bottom the idle will stay to high, now it is time to lower the idle to were it belongs by re adjusting the idle screw!

slayerphonics

tuning is an art form, I hear so many opinions on how to tune, one pro says my engine is tuned perfect next pro says no it has a rich low.. gotta love nitro,

hilifemt

I think Ron described it quite well and accurate. People do overcompensate the LSN with a poorly tuned idle and vice versa. Like slayer said, it's an art form. I can tell where my tuning needs adjustments just by seeing and hearing my engine. Takes me about a minute to get it fine tuned. Hard for me to describe tuning, but easy for me to fine tune. hahahah

Argess

too funny slayerphonics.......and I think very true......let's see what other opinions we can get.......more knowledge may equal more power......

RBMike

Ron Paris knew what he was talking about. He devoted most of his life to the RC industy.

bentgear

Argess, I think you are confusing what he was trying to write with what you are thinking about when you adjust your low speed needle. The pinch test will not reliably always tell you much about having your slide or barrel being held open too far by the idle adjustment screw.

Ed M.

Argess

I guess what I am saying, is if you reduce the finely tuned "high speed" idle by adjusting the idle stop screw, you may have trouble with a stalling engine if it idles too long. i.e. when it loads down with fuel, it may stall.

Also, I never liked the sound of the high speed idle when letting off the throttle. Sounds like it is too lean. Sounds much easier on the engine when it drops to the lower speed "rich" idle...or possibly 4-stroking.

By the way, I would never question the competency of Mr. Paris. I'm just trying to understand what he is recommending and see if I am doing something worng. Until I read his recommendations, I was comfortable tuning the way I always do. Now I wonder....but thanks all, for your comments. I appreciate them.

bentgear

What Ron was trying to put in words was his method for getting the idle screw set right. No where in there does he even go into setting the low speed mixture screw correctly, he is just getting you to a point where it can be set.

Ed M.

125cchyperman

What bentgear said, Mr. Ron Paris spent his life devoting it to rc engine's and such. I would never question anything that he said, he was the Einstein of rc engine's. But as bentgear said I think your kidding confusing two things here. He never went into hwo to set the LSN screw. Just that some people overcompensate for a baddly set LSN with a high Idle setting.

chadwright

I am a nitro newbie and I am almost positive that I am having this problem..I ahve a MGT 4.6 truck and have just went through the break in last week..I was working on tuning, which is my first time and i have this exact problem. I can take a high speed pass and bring the truck to a stop..the revs are still really high for about 10-15 seconds, then it will idle down for about 3-5 seconds then die..does this sound like what i might be suffering from? I have a small temp gun and am running the truck with the top off. What kind of temps should i be looking for and when do you check them...do you make a high speed run and stop the truck right by you and check it then, or do you run it and then let it idle a little then check it...it fluctuates so much...thanks for any and all help for this total newbie who is having fun

Chad

fasstrevo

Ron Paris was dead on! That is how you properly tune a lsn.

*FULL-REVS*

^^^^^ sure is.... if you read that whole artical.... it all makes sence.... someone got a link for others that want to read it? the first time i read it i just sort of skimmed it... and got some of what he was saying wrong.... so if you do read the artical take your time doing so....

Argess

OK....to narrow it down, here's the part that interested me:

"the idle is low because the low speed mixture adjustment is set so rich that the engine loads up with excess fuel and the engine goes into what’s commonly called a four cycle idle.
One tell tail sign of this is if after reving up the completely warmed up engine it tends to idle fast for a few seconds then drops to lower idle speed."

Well, that last line is pretty much the way my eninges work after I tune them. Regardless, I am going to try his method....once the weather warms up....still winter here.

If I understand his method, I need to continue to lean the lsn until the engine no longer drops to the lower idle speed after getting off the throttle......then re-adjust the idle stop screw to reduce the now "permanent" fast idle.

Thank-you for all of your comments.

ps: please dont' confuse my posts with trying to challenge Mr. Paris's methods. I just like to understand what I am doing. What keyed me on this particualr recommendation of Mr. Paris was that all my engines seem to run hot at best tune.....about 270F. If this is because I have too lean an HSN, I want to find out. I can see this happeneing if the lsn is too rich. Under full speed, it relies on using up that extra fuel, but once it runs out during that high speed run, the engine leans and heats up more than it should. I think that is what Mr. Paris was getting at.

bentgear

Argess, I think you are getting a grasp of what he was trying to convey. It all boils down to the fact that before you can get a perfect low speed adjustment, first the idle screw must be in very close adjustment. I think he was giving better instructions that the common make sure the slide is open about 1 mm when at idle.

Another way to do the same thing that "sometimes" works is after running a couple of minutes bring it in, take a temp reading and let it idle. If after a short time the temp falls like a brick you can bet you have this problem or you are running way too lean on the top end and using the bottom end to compensate.

Chad, if it is dying quickly after that return to idle then you may be too lean. If it is loading up and then choking down you may have this problem. A quick turn of the screwdriver will tell.

Ed M.

Argess

Thanks Benty. And sorry Chad....I sort of missed out on your post. You seem to have your engine tuned like I normally do, however raise your idle a bit with your idle stop screw to keep it from dying.

This thread sort of discusses leaning it out to maintain that temporary high idle. So you could just lean the lsn to keep that idle up. But I havn't tried that. It's why I am asking about it here.

As far as temps go.....I frequently get about 270F during most of my runs with temps just getting close to 300F as the tank runs dry. More like 260F when the tank is full. Most people tell me that's too hot, but any richer with the HSN and it's a slug. That's with 20% nitro and a cold plug, and it seems fairly consistent regardless of what engine I am using. I am limited in brands of fuel I can easily get, and I have got better results with other brands that arn't currently stocked by the hobby shop closest to me.

And "yes", make a high speed run, bring it in, and immediately check the temp as it will cool at an idle fairly quickly (both from the richer setting and the fact the engine load is gone). Try to measure at the glowplug, not the cooling fins.

slayerphonics

Id recommend going to a medium to hot plug on 20%, could help you out

chadwright

I do beleive that mine is loading up then choking down..If i run it at 1/4 to 1/2 throttle it sounds as if it is "loaded" up and doesnt clear at that throttle range..It does clear and runs well at full throttle.. Run it at full throttle and run it back to me at full, stop immediately right next to me, temp will be 240-250 and the idle will be really high, almost to where the truck rolls forward, then about 5-7 seconds the idle lowers to a lower idle for about 5 seconds then dies..any help would be appreciated...frustrated, but having fun

Argess

OK....having had enough speculation, I decided to brave the winter weather (actually not too bad today) and give things a try. Here's what I found out:

Number 1:

Symptom: Engine drops to a high idle after getting off the throttle, and after a while drops to a low idle

Cause: HSN is too lean. The lower idle is correct, but it takes a bit for the engine to richen up enough to run fine.

Note: A too rich LSN may also be the cause (set that way due to a too lean HSN), and I think this was the point Mr. Paris was talking about.

Number 2:

Symptom: Engine drops to a normal idle after getting off the throttle, but then gradually speeds up

Cause: LSN too lean. Engine is running out of fuel

Note: HSN may also be too lean.

Summary:

OK....I have new-found respect for the job the LSN does. Usually I set it a bit rich, the idle remains constant, the engine will idle all day and the acceleration is OK....because it's close to a good tune. Basically, I only have to re-tune the HSN depending on weather, humidity, etc.

I have found today that further gains may be made with fine tuning (leaning) the LSN more, but when you do that the relationship between HSN and LSN becomes much more apparent and the HSN setting can REALLY affect your idle. And I think that's what Mr. Paris was pointing out.

In the end, my buggy works awesome....by leaning the LSN a bit more than I always used to do. Mind you, I was happy enough with it before, as it was "close". One positive thing about leaving it with a rich idle......you can leave the LSN alone pretty much from then on and only tune the HSN for weather, etc. However for max performance, Mr. Paris was right, and if I didn't grasp what he was trying to say, it was enough to get me on the right track and I'm happy now.

Thanks all!

RBMike

Did your temp come down?? Some will argue with me but 220 to 240 deg F is a good temp window (cooler on a winter day) but ALWAYS check for good smoke. Do not count too much on your temp gun, good smoke is very important. The cheap temp guns we RCers tend to use are very innacurate & prone to error.

*FULL-REVS*

cant always rely on smoke either as different brands of fuel run different ratio's of oil and different brands... some smoke less than others... people need to "listen" to thier motors learn/know the sounds they make when they are lean or rich...

Argess

No, my temps didn't come down with the recent tinkering as I was already close. But I have had some success in the past with reducing temps by leaning the LSN and slightly richening the HSN, yet still keeping good power.

I usually use an A5 glow-plug (cold) as I typically have engines running hot. In non-OS engines, this shorter plug also reduces compression a bit, and that helps keep the temps down. My engines run hot due to the fuel I use (Sidewinder Sport - only thing available locally) as well as the large wide-open (with grass) spaces I run in. Note that I have found Sidewinder Backyard Basher fuel to run very hot....I think due to all the oil in it, artifically increases compression (oil doesn't burn, but takes up compression area space).

Certainly, until recently I have been running with the LSN to rich. As Mr. Paris states, this can cause me to set my HSN too lean to compensate, and then things get hot on long straight-aways once the excess crankcase fuel burns off. I always leaned the LSN until the pinch test worked and then a bit more until the vehicle would acelerate without bogging. This was close, but too rich for best idle perfomance, and sometimes rich enough I would have my HSN set a bit too lean.

A slightly "too rich" idle is kind of nice.......you can do a daily HSN adjsutment and keep the engine running well wihtout having to re-adjust the LSN. The idle merely goes from a bit rich to a bit more rich, or a bit less rich and always stays stable. But it is not the best for wheel-spinning acceleration from a dead stop.

I think where I was confused was this idle settling down to a 4-stroking thing. My engines were tuned close enough they wern't doing that, but I thought maybe they were after I first read the Paris-Tuning method. In my case, the idle reduction rpm a few seconds after getting off the throttle seem to be from too lean a HSN. I say that because the high idle I was getting sounded "lean" and "nasty", while the final idle sounded smooth, not "blubbery". I think that might be Chad's problem above.

Whew.....seems like I am writing a novel, but perhaps this thread will help someone else, and that would be a plus. I know I've learned something. Thanks again everyone for your inputs.