# Tuning Tips from Ron Paris



## cjtamu (Sep 22, 2004)

I was luck enough to copy this off their website before Ron passed away. Great info, I think Jeff Schwartz has it posted on his site somewhere also. I have some Q&A stuff from the Paris site that I'll post later after I sort it:

Tuning tech: carb Needle balance

We get dozens of tuning questions from around the world at Paris racing daily, The number one questions is, were do I set my needles on the carb? Unfortunately there is no such thing as a definitive universal setting for any engine!

Every application will have it's own unique requirements, even two IDENTICAL set ups can and most likely will have at least slightly different settings.
Please see tech tips following the article below [from our web site]
I would like to address what seems to be the # 1 mistake we encounter in engine tuning:

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!

CAUTION!!!!

Now that you have the idle set correctly the top end may be too lean!!!
Keep in mind the fuel does not directly enter the cylinder area like a 4 stroke engine, it enters the crankcase area first then is transferred or pumped up to the cylinder area by the piston movement.
Simply put, the crank case volume can hold much more capacity than the cylinder so it takes some time to burn off the residual fuel.

In other words if the bottom end is to rich the engine will be supplied by this residual fuel briefly and depending on the demand you may be actually be experiencing a lean condition on the top end that can range from:
1. Seems to run well but engine life is short
2. Seems to run well but car continues to get hotter the longer you run to the point of overheat!
3. Seems to run ok on the bottom but sputters starves or strains to gain rpm
4. Seems to run ok on the bottom but when I give full throttle it cuts out or stalls
[An overly rich top end can act the same as 3 & 4 but excessive smoke and oil are usually present with a distinct blubbering sound]

There is no reason for an engine to continually get hotter unless the tune is wrong [classic #2. symptom] or there is a mechanical problem causing more load or drag on the engine as the run continues.
Exception Note: if the weather or track conditions change DRAMATICL Y. {Examples}
A light drizzle starts and the off road track goes from a very dry loose to high traction condition, or during a race a rapid weather front like a ten degree change! It is very important to fully warm up your engine, clutch and chassis before making finale adjustments.
The chassis in most applications also works like a heat sink to the engine so it is important to fully saturate the chassis!!!

I like to start the engine at least 3 or 4 minutes before our qualifier to get some heat in the engine.
[Operate the throttle by hand until you have radio frequency clearance]
It still takes at least 2 to 3 minutes of hard running on the track to fully saturate the chassis!

There is a series of restrictions to control fuel flow at different throttle/air flow positions called needles These are the five basic parts of the carb to concern yourself with:

1.The slide or barrel [regulates the amount of air to enter the engine controlled by the servo]
It simply blocks off the airflow to the engine proportional to how far it is open or closed.
2. The idle/air speed screw [sets the absolute minimum air the barrel/slide can control to maintain idle speed]
It simply is an adjustment screw that comes in contact with the side at the nearly closed/idle position.
3. The high speed needle [regulates maximum fuel flow allowed to enter engine at any throttle position]
It simply is a tapered needle that screws into the fuel flow orifice [an adjustable restriction] .
This maximum fuel flow ideally is adjusted to the correct mixture ratio for the surrounding conditions at WIDE OPEN THROTTLE or WOT
There are two more devices' the low speed or minimum spray bar and the mid range needle that restrict or control the fuel further at less than full throttle.
4. The low speed needle [regulates fuel to engine at idle]
The low speed adjustment simply restricts the flow at idle speed.
If you look down the bore of the carb you will see a long tapered needle [except for Picco torque carbs]
When the carb barrel/slide is closed the larger part or diameter portion of the long tapered needle is inserted into the spray bar, this is what's adjusted when you turn the low speed/minimum adjustment.
It literally moves either the tapered needle OR spray bar farther in or out changing the restriction independent of the barrel/side position.
This leans [more restriction] or richens [less restriction] the flow from the spray bar at idle.
NOTE: some carbs the spray bar is moved and others the needle assembly is moved, both have the same effect.
5. The mid range needle [regulates fuel to engine after idle and before full fuel position.
Notice as you open and close the carb the tapered needle [mentioned above in item 4.] enters into a small tube this is called the spray bar/jet.
This spray bar is were ALL the fuel enters the airflow stream regulated by the high speed, mid range and idle/minimum adjustments!
Normally somewhere between Y2 and % throttle open position the needle is completely out of the spray bar, This is what is called full fuel position or FFP [at this point 100% of the mixture is controlled by the high speed needle.
On many carbs the low speed and midrange are not independently adjustable so the mid rage is a factor of the needle taper and is engineered by the
factory. On some SLIDE carbs there is both independent spray bar and mid range needle adjustments. CAUTION: be very careful with these type carbs!!!
You can identify them easily because there are four adjusting screws!
0ne each for the:
High speed/top end [normally sticks up some what vertical]
Idle/air speed [normally a much smaller screw entering the carb at an angle]
Low speed/minimum [located in the end of the slide OR on the opposite end of the carb body]
Midrange [also located in the end of the slide OR on the opposite end of the carb body]
Note: if there are adjustments on both the slide and the carb body one is an adjustable mid range and the other the low speed!!! Check with the engine manufacture before attempting to adjust these types of carbs!

It is very important not to use the mid screw to adjust the low end by mistake; it is very easy to get the carb way out of sync.

Normally I recommend not attempting to adjust the mid range even if your carb is so equipped, the gains are VERY small and mostly limited to minute midrange drivability/economy changes that only the most sophisticated driver will recognize!

The negative is a carb that is so screwed up only an expert can get it back in tune!
Please note the above descriptions will apply to 99% of the modern car carbs being manufactured as of this writing with the exception of the Picco TORQUE carb that use's no mid range needle at all.
It utilizes a fuel management ramp built into the slide; the carb also has two completely independent fuel delivery spray bars/jets.

I wish I could tell every one exactly how to tune their engine but I cannot!
My hope with this article is if I can help racers to more understand How your carb works, all the other instructions and guides will make more sense!
Best Regards,
Ron


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## cypressvendetta (Nov 9, 2008)

CJTMU: good info thanks!!


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## Courtney Vaughan (Apr 11, 2007)

I have this as well, and tell people about it ALL the time! I used to always wonder why my motors didn't run like some of the expert guys, and then I read this article, practiced it for about 3-4 months, and now have motors that run just as fast as anybody's, stay cool, last 5+ gallons, and rarely flame out. This is the ONLY method for good tuning technique as far as I'm concerned!


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## Gary (May 21, 2004)

Never did learn much about nitro but I remember Ron. He used to get his write ups posted on the Starting Grid magazine back in the day. I remember another excellent write up printed in the SG magazine about how to tune a stock motor back in the day. And that same guy won the "Most helpfull RCer" of the year award!


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## Donnie Hayden (Mar 7, 2005)

CV, your motors never lasted because you never drove them fast enough


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## PD2 (Jul 1, 2005)

Novarossi used to hand out those tips with their motors too for breaking in and tuning their motors. Old Nitro Dan from ANTR did too - miss that guy sometimes.

Definitely good guide!

PD2


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## Courtney Vaughan (Apr 11, 2007)

Donnie Hayden said:


> CV, your motors never lasted because you never drove them fast enough


said the man who never races anymore!!!!!


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## kstoracing (Oct 30, 2008)

I read the guide twice and still don't understand it. Maybe next time one of you guys can help me with my motors...lol.


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## Donnie Hayden (Mar 7, 2005)

Tuning is some what of a pain. Once you get to know how the motor should sound and perform around the track, it sticks with you.

CV, we are trying to purchase a house right now. Once that is done, I might come back out.


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## Courtney Vaughan (Apr 11, 2007)

Karl.....you coming to the River Race on 1/31? If so, I'll go over it with you and help you out. Donnie is right: once you get it, you get it and you really won't even need to use a temp gun because you can hear/see/feel how it drives/runs when it's tuned right.

I'm JK with you Donnie. We'd love to see you racing again though.....you've taken too long of a break! Where are you looking at moving to?


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## Courtney Vaughan (Apr 11, 2007)

Karl, 

I had a few minutes to type you a little more info to try messing with on your motor. What I learned from this guide was to start with the bottom end tuning first, instead of the top end (like the manuals all tell you to do). The key is to get the motor to fall back down to idle as quick as possible.

To start, put in a fresh glow plug. Make sure your throttle/brake linkage operates properly. When you pull the throttle and then let the servo go back to neutral, does the carb go back to the idle gap? Does it close a little further when you hit the brakes? If it does, then it shouldn't. You want the carb to go from open and when you let the trigger go to neutral or hit the brakes, it should return exactly to the closed idle gap EVERY TIME. Again, if it doesn't then you need to play with your linkage and trim adjustments. Once that's done, then fire it up and make sure your motor is up to temperature before you start tuning on it&#8230;&#8230;this may take a good ¾ of a tank or so, but you're wasting your time tuning if your motor isn't up to temp.

From there, pick your car up and put it on your starter box or a stand&#8230;&#8230;.keep it running. Now, you rev your motor up and clear it out, and let the throttle go back to neutral. What you're listening for is to hear how quickly it goes back to idle, and if it stays there. 

What did it do? 

Did it slowly make its' way back down to idle? 

If so, try doing it a couple of times and counting how long it takes to get back to idle. Then LEAN out the BOTTOM end needle about 1 hour and repeat the "rev up, clear out, and let it go back to neutral" process. What did it do now? Did it take less time? If so, but it's still taking a little while to rev down to idle, then repeat this process about an hour at time. The goal is to get the motor to go from rev'd up and clear out, let the trigger go to neutral, and have the motor fall back to idle RPM's as fast as possible (usually ½ second or less). You may be surprised at how much you'll have to lean the motor out on the bottom. You'll know you've leaned it out too far when you pull the throttle and it hesitates/bogs and then revs. If that is the case, then you need to richen the bottom end. Also, as you do this, you'll need to throw your car back on the ground/track and run it around a little in between adjustments, as the tuning can vary slightly under load. You may find that you've got it set to where it falls from high RPM to idle just right while it's off the ground, but you drive a lap or two and it start to hesitate or bog on the track&#8230;&#8230;..richen it up a little on the bottom and repeat the processes.

MAKE SURE TO GO ONLY AN HOUR AT T TIME ON ADJUSTMENTS!!!!!!

One thing you'll also need to keep in mind is that during this process, you'll find that as you lean the bottom end, your idle RPM will rise up. So, after you've gotten the bottom end set closer to where it falls from high RPM back to idle RPM quickly and consistently, you'll probably need to lower your idle using the idle gap screw. Play with your idle screw until the car will idle on the stand/starter box without engaging the clutch. It should idle, but not high enough to turn the wheels. It should idle for 15-20 seconds without dying. It shouldn't have to idle all day, as you'll never do that to it when it's on a track.

Once you've got that done, your 90% of the way there. Just tune your high end needle to where it clears out and goes to full throttle while still spraying some smoke out the exhaust.

If you've got a temp gun, use it throughout this process. Optimal engine temps will be 220-250F. Some motors run a little hotter. If yours does, just ALWAYS make sure you're seeing smoke from the exhaust. 

Try this out and let me know how it goes.


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## Donnie Hayden (Mar 7, 2005)

We are going to stay in the Texas City area still. I would love to come hang out at the river track on the 31st, but that is the monster truck show weekend and the car show weekend.


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## kstoracing (Oct 30, 2008)

I usually use the pinch test for the low end. Where it Revs a little then dies after a few seconds. I am going to have to try this method it seems very interesting. 

CV, dude thanks for the write up...lol. It just look like it took a while to write. I guess because it would have took me a minute to write it up. Thanks, I believe I can get mine to run like you said. I just have to set some time aside for it then.


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## cjtamu (Sep 22, 2004)

Bump for Guff.


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## Guffinator (Aug 27, 2005)

Thanks Chris, I already have it though.


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