Originally Posted by Trevor Williams

Monty,

my plus4 you pre-broke/tuned for me is at 3 1/2 gallons, it still has a TON of compression, and makes sick power and gets killer runtimes....I Set TQ/won the A with it yesterday @ St Louis Dirtburners club race. The engine is just amazing, and seems to get better every time I run it(kinda like the Losi)
Anyways, just wanted to give you a big ole' thanks for hooking me up with a killer engine that I dont have to fight everyday at the track

Bro, think its ready for ceramics? no leakage, but I may as well

Originally Posted by USP45

Hey Monty, I have a few questions for you.

First, I had an in-tank line split today during a race after about 4.5 gallons through the engine which caused it to go very lean, when I noticed it (hard to hear the engine with 11 others going unfortunatly) the temp was 303 degree's. Afterwards the compresson felt a little low. When cold it will hold compression forever when you hold the crank so that the engines weight is trying to turn it, and it still has very slight mechanical pinch. When heated to 230-240 it will hold the engine for 2-3 seconds but still pops over pretty good. Is there any way to tell when you need to be pinched? I hope that the hot run did not hurt anything, the top of the sleeve/piston are non-scored, very shiney, and it starts building compression right after the piston goes past the exhaust port but it hardly has any mechanical pinch when cold as I said.

Next question is based of the need to eventually replace the piston/liner. Basically do you sell them and how much? I measured the rod bearing and crank pin, it hardly has any wear, I measured .01 parallel with the rod so I think that it is still good. The engine has only been started cold once and this was well after being broken it. Otherwise it has been started with a heat gun, or more recently a Powerhouse engine warmer.

Also, do you have something like an o-ring kit for the engine? Something to replace all o-rings and the aluminum rings that go above and below the banjo fitting on the high speed needle.

I was going to PM you but I figured some others might be interested in knowing some prices as well since more and more of these engines are showing up at the track.

Thanks for the help with all of the questions.

Originally Posted by air8

Dam it, excuse my French. I just waited like 4 hours for my video to upload only to find out that videos longer than 10 minutes get removed?????? Gahhh. C'mon? Seriously?

Monty
If you are interested in watching a single truck fumble around the track for 12 minutes I'll email it to you, if it's allowed in emails. IDK. I've never tried to send a vid to anyone before.

Originally Posted by USP45

Very good, thanks Monty. It was not at those temps very long, not even a minute I do not believe. Funny though, those temps are not out of the ordinary in an airplane engine, especially while hovering.

Anyway, shoot me a price on the o-rings when you get a chance, the aluminum ones aren't leaking so no need to bother. Some of them are kind of chunking, the upper on the low speed, the upper on the high sped, the lower carb seal, and the back plate o-ring is kind of flat now. It may be doing its job but it doesn't hurt to replace it.

Are the o-rings in these engines anything special or just run of the mill o-rings? The ones on the needles look different, I might pick up several to have handy.

Thanks again

Originally Posted by USP45

Yea, shoot me a price on full packages.....which are how many?

I only take them out when I flush and clean the carb. Even with a fuel filter sometimes little pieces of crap get it so about every half gallon to gallon I pull it and use carb/choke cleaner to flush it out. Maybe unnecissary but I gt bored every now and then.

Originally Posted by houston

ron knew nitro engines

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
some stuff doesn't apply to our engines today but they are still excellent guidelines to follow as we all learn more about the nitro engine and how to master the art of power extrapulation . i spent a few years learning all this stuff by myself before i ever read any article buut ron is always right on the money
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Originally Posted by clebo3

Monty,

I would like your opinion on fuel. I currently have a 09 +4 with about a gallon on it. I run Bryon's 25% currently, but my lhs closed and the others in the area only carry Bryon's 20% or 30%. Should I go through the hassle to get 25% or can I just run 30%. If I do change do I need to change or add anything. Thanks for any advice.