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Talk about rc car nitro engines and gas engines
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by: ozgurcoteli
well a lot of the posts on here are for tuning. A lot of people are hisitent about getting into nitro because of the hassle of tuning a nitro engine. I would to if im investing big bucks and knowing if its not tuned right or broken in properly then i have the potential to ruin my valuable investment. Im going to use some of my knowledge and experience to help you guys out. A normal carb that most beginners and most nitro enthusiats buy are two needle carbs. Two needle carbs include the LSN which is the acronym for Low Speed Needle and the HSN which stands for High Speed Needle. Some engines out there have a MSN(i htink if im wrnog please correct) it stands for middle speed needle. All of these needles play a HUGE factor on how your engine is to be run. Each needle also does somethign different and when all of them are combined correctly they give the engine a strong powerband(low to high). There is a another screw called the idle speed screw. This regulates how fast the idle will be(not throttle applied)

Lets starts with the low speed needle (lsn) i will be using the acronym through out this guide. The LSN has the function of the acceleration and how well the car starts up. it regulates how much fuel it "uses" during idlign and the low end of the power band(acceleration and a lil higher then that). this needle is found right next to where the engine hooks up with the servo. i will try to post a picture of what it looks like so you get an idea.

Next we have the high speed needle(hsn) i will be using the acronym through out this guide. The HSN takes over when the LSN has reached its max i nthe power band. so on many engines this is used for the middle and full throttle. this needle is always tuned before the low speed needle is tuned. many times during races or bashing. if a car starts to over heat you usually have to richen up the HSN.

Now there is a Idle speed screw. this screw is a pointed screw and pushing out on the barrel or slide of a carb. as it pushes it out this is the idle setting for the car. ALWAYS adjust the idle speed screw while applying a little bit of throttle or shut off the engine and give it full gas, then adjust the screw.If not you have the possibilty of bending the pin or the needle tip if you dont. Most engines are maxed at 1mm- 1.5mm out from completely closed. so the gap should be 1mm-1.5mm closed(hence you do not need the car runing to adjust this). this needle is the long needle sticking up(cant miss it)

Ok now that we are associated with the needles and what they do. lets actually get to the starting part. All engineshave factory settings and all engines have to be broken in when bought new. Breaking in an engine doesnt mean actually breaking it lol, but rather wearing in the piston and sleeve to the right fit. Each engine is engineered to have its own procedure. There are some general break in steps, but I STRONGLY reccommend you download a pdf file for the engine through the company or if you have instructions to look at their factory settings and break it in through there ways. YOU MUST BREAK IN THE ENGINE it is a MUST.


When buyign fuel ask around your local hobby shop to see what the MAJORITY of the people use. Fuel must be chosen through the weather and climate of your area. if the higher you are or if you live in a colder climate you dont need 20%, but you can get away with 10 or percent. this is because the air is already cold and it is thinner. visa verse for opposite conditions. REMEMBER: what ever percentage you break in your engine with stick with it for the life of the engine. Brand can be exchanged just not percent.

After you have done break in it is time to tune the engine. There are many factory that contribute to tuning a engine. Weather, glow plug, engine, air filter(if it is overly oiled), track and runnign conditions, and fuel percentage. NEVER tune on the first tank. You can but you will have a hard time. This is a mistake everyone does. Allow your engine to warm up and just put it around. Obviously if your engine cant start then you need to tune from start or refer back to factory. Fctory settings are great because they are rich settings and allow you to have a "Home base" when things get hectic. So when ever you are having major problems never hesitate to start off from factory settings. you will save your self from a lot of headaches( factory settings can be found in your manusl or downloadable pdf files).

Alot of times a engine will not run or start due to maintanence issues. So, before i help anyone tune or even touch the needles I tell them to make sure all thier head bolts are tight, their glow plug is good to go, if the fuel lines are good, if the fuel is good to go and not too old(bech life is like a year. i run old fuel no harm done ust quality goes down) and if the glow ignitor is charged. A lot of the times these issues are what causes normal problems. If all this is good to go then go ahead and refer to factory settings. After you have done this check to see if your idle speed screw is set to 1mm-1.5mm gap. put the glow ignitor on and fire her up(should start up, but may take a while). dont be afraid to give it a lil gas like 1/4 throttle. If you get into higher tech stuff people use idle up to start thier cars. What i do is i take the wheels off the ground and blip it at 1/4 throttle (no mroe than that). Usually there is a time when the engine first starts up where it needs the initial warm up and clear the fuel out of the crank case. A lot of racers do this so they dont build up fuel while idling. It does not harm the engine if you blip it at 1/4 throttle. just only do it a lil bit until she is warmed up. i can not stres enough to not go past 1/4-1/2 throttle. ok after she is started and running drive it around for a while and notice what it needs to be done. if you notice it is sluggish while accelerating or you see a bunch of fuel and smoke while accelerating, then you know the LSN needs to be leaned. as you accelerate into WOT(wide open throttle) and its not reachign its full potential then you know it needs to be leaned. Tuning must have a ear for. you might be saying what is its potential. Well this is through trial and error. while at stock setting richen the hsn up a tad and hit wot. Listen for the difference. now lean it back out to factory and a 1/16th of a turn lean from factory. listen for the difference. as you tune you must acuire a ear for the engine peak. Factory settings are always rich so you will most likely be leaning it out from there.

After you have run your first tank for the day(remeber break it in before doign any of this) now its time to tune. As you noticed what needed to be done during the 1st tank start by tunign the hsn first. Start the car with body off, the fuel tank fueled up , warm the car up by doing high speed passes. you will most likely have to tune in from factory. so after it is up to temps(buy your self a temp gauge) like arond 200 is good since its rich. start by leaning it out the HSN 1/8th of a turn. you should see a difference now. it should seem quicker and the engine will get to the higher end of the power band. Look for a trail of thin smoke as you hit WOT. make sure there is smoke. Bring it in and check the temps. you will notice an increase which is fine but remember your limit from the manual. if you leaned it out only 1/8th and you hit your limit then you do not need to tune any further and your engine is peaking out or has a air leak somewhere. if you have room to lean out further then do so 1/16th of a turn and do some WOT passes. always look for that thin trail of smoke from the exhuast throughout the power band. Bring the car in and check the temps. should go up, but remember that limit. If you are running a 2.5 do not exceed 270 degrees and if you are runnign os i would sty within 250-260 depending on the engine. Most areas have their own sweet spots and you must find that. ok if you have room to go then lean it out 1/16ths of a time and repeating what you have been doing. If you have been running and the car is not gettig any faster or the temps have been staying the same or hitting close to thier limits then this is the peak of the engine. learn to love it because this is your goal and you dont want to exceed it. you will develop an ear for what douns normal and what is peaking out. while you are out running. try runnign with experienced people as they will also have tuned cars and you can hear thier pwer band and whats a engine sound like peaking out. i will try to post a few videos of what a engine peaked out sounds like.

After you have tunesd the HSN, it is time to tune the LSN.Ccheck to see if you are low on fuel in the tank(i would say maybe a lil less than half shold be the limit only because you do not want to run out while tuning). If not then fuel up and do some high speed passes to get that fresh fuel in there, if you have fuel then neglect the the first part of the sentence. Do some high speed runs and clear out the crank case. Bring the car in and grab some pliers(body is still off). find the half way mark on the fuel line and squeeze the fuel line. The car should take 2-3 seconds before it stalls. If the car takes longer than 3 seconds to cut out then lean the LSN out a bit and re-try until it takes 2-3 seconds to cut out. If the car takes less then 2 seconds then richen up the LSN and re-try until you get 2-3 seconds until it cuts out.

After you are done with all this bring the car in and let it idle. As the car idles it should stay perfectly still and not trying to spin the spur gear(gear attatched to the clutch bell). If it is trying to engage it then shut it off and unscrew the speed screw just a TAD and fire her up and see if it is normal. If the car requires throttle to start and your engine cuts out when you bring it to idle. make sure your gap is open enough. so shut off the engine and screw in the speed screw a lil and see what happens. it should be enough where it is not engaging the cluctch, but its enough to keep running.

Alot of the times you will need to re-center your servos. Do this by takign of the horn and make sure the car is off. Center the trim on the radio and turn the car on. ok next push the throttle arm al the way close and them ount it back onto the servo. make sure you are at 1mm-1.5mm gap and make sure when you put the horn back on that the linkage cannot close the barrel or slide any further. Because when you apply brake you do not want it to open or close the barrel. there is a little spring on the linkage that conncts ot the engine that is supposed to engage.

Basically that is tuning 101. Low speed needle measures low rpms and high speed needle does mid-high rpm. if the accelration or high speed feels sluggish then lean it out and if its to lean richen it up. Moderators im going ot ask if you can pin this up to the top. I think this will help A lot to new users and help experienced users contribute more to this guide. I hope people add more and patch up what i may have missed. i will post illustraitions of the needles and a video of a peaking out engine.

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