hpi apollo
Posts: 2639
Joined: 5/13/2006
From: Georgetown,
KY, USA
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well since RCU wont let me edit my original article anymore, here is the FAQ section, which was written by the other guy in my group, and for the love of God please don't start this flaming crap and counting grains of salt (it's not perfect, get over it)
Top end needle valve(also known as High end needle valve, main needle valve, etc.) â this is the mixture screw on an R/C engine that is usually the largest of the potential 3. It will usually reside on the carburetor body either facing straight upwards (perpendicular to the ground when the car is sitting on the ground) or slightly off. Most of the time, it is housed inside of a bronze or gold colored housing.
Low end needle valve (also known as Bottom end needle valve) â this is the mixture screw on an R/C engine that is located on either the rotating arm of a rotary valve carburetor, or on the end of the slide of a slide valve carburetor.
Midrange Needle valve â This is the mixture screw that is located opposite of the Low end needle valve. It is used to fine tune the mixture setting on high end racing engines. Sometimes, it is included as a marketing gimmick for sport engines, but should never be adjusted until you are very experienced at tuning engines.
Lean â Fuel mixture setting where not enough fuel is getting into the engine. On an R/C engine, we correct a lean setting by turning the adjustment screw (needle) counter-clockwise (as if you were loosening the screw).
Rich â Fuel mixture setting where there is too much fuel entering the engine. On an R/C engine, we correct a rich mixture setting by turning the adjustment screw (needle) clockwise (as if you were tightening the screw).
Flooded â An engine that is flooded has too much fuel inside of the combustion chamber and/or crankcase to actually start and run. It may pop and fire, but it will not actually run.
Hydrolock â Condition describing a situation where an engine has too much fuel inside the combustion chamber and crankcase. This is an extreme example of an engine that is flooded.
Vaporlock â Condition describing a situation where an engine is actually hot enough to evaporate the fuel from the carburetor before it enters the crank case or combustion chamber of the engine. This can make an engine nearly impossible to start until the engine is allowed to cool at least 5-10 minutes.
My engine slows down and dies after idling for more than a few seconds (long enough to let a car pass by or during a pit stop). I must sometimes de-flood it to get it to restart (Hydrolock). It is also sluggish off the line and spills quite a bit of oily gunk out of the exhaust.
This is caused by a rich mixture setting. If your engine idles down lower and lower until it dies, try leaning it out 1/8 of a turn and see what happens. 1/8 of a turn often is not enough, but if the condition seems to improve, keep going until you find the sweet spot.
After running for a few minutes, my engine dies and I have to wait several minutes before I can get it to restart. It ran great right after I started it. What could be wrong?
This is usually caused by one of three things.
Too Lean: Your needle settings are too lean (especially top end needle). Try richening it 1/8 of a turn at a time and see if the condition improves.
Too lean can also contribute to another side effect of Hydrolock. The remedy is the same. Richen the engine.1/8 at a time
Worn out: unfortunately, after time, nitro engines do wear out. If you are running a rich mixture setting and no overheating is occurring, but it still dies and must cool before restarting, you are most likely due for a rebuild or a new engine.
After several minutes of running, my engine dies. I canât run it any richer without having it bog down, and itâs not overheating. Any ideas?
This can be a sign of too hot of a glow plug. If richening the engine doesnât stop it from flaming out due to high temperatures, try a colder glow plug.
My engine cuts out right off the line, but seems to be okay once itâs got some rpm built up.
This is normally a sign that your bottom end needle is too lean. The engine is cutting out because it does not have enough fuel for strong acceleration. Correct this by richening the bottom end needle in 1/8 turn increments until the condition is rectified.
My instructions say my engine may run around 280 degrees. However, itâs running at 220 degrees right now, and it seems to be doing fine. Should I lean it out?
NO! Many times, engines will run at what seems like an abnormally low temperature compared with what you may read or see elsewhere. Do NOT tune by temperature. Your High Speed Needle is not a thermostat.
I bought a giant cooling head and now my engine runs poorly. Why?
The problem with many aftermarket cooling heads is that they are simply too large to be functional in most conditions. If you live in a very hot and humid environment, sometimes it is necessary to purchase a larger cooling head to keep the temperatures within the reasonable range. However, in normal climates and in colder weather, most times an aftermarket cooling head will simply make your engine run so cold that it will never actually reach operating temperature. This is not only hard on your engine, but will cause a performance drop as well.
My engine runs inconsistently. The idle may be good at one time, but floats around other times. Also, sometimes it runs great on top end, but other times it cuts out or even bogs on top end. Iâve tried richening and leaning all I could. Any ideas?
Try resetting your engine to the factory needle settings. If this does not work, you may have an air leak.
Be sure there is absolutely no oil or fuel anywhere that it shouldnât be. Check the fuel tank for pressure, and replace fuel lines. Also, make sure your gaskets on your engine and between your pipe and manifold are not leaking at all. If this doesnât work, seal up the carb and replace o-rings as necessary. Check the head bolts for tightness and make sure fuel isnât leaking around the glow plug.
Sometimes, unfortunately, this can also be a sign of blow-by in the combustion chamber. This is most commonly caused by foreign materials being pulled through the engine, but can also be a sign that you have simply ran the engine through its life cycle. Time for a new engine or a rebuild!
My engine will run OK for a bit, but sometimes randomly shuts off. It also seems to be running as if it was rich, but leaning just seems to make it worse. And if I lean it too far, it shuts off but still seems to be rich.
Most of the time, this is caused by either bad fuel, too cold of a glow plug, or too low of a nitro content in the fuel. First, try a new glow plug, or maybe a hotter plug. If this doesnât work, a new jug of fuel might be in order. If it turns out the new fuel doesnât do the trick, you may need to bump up the nitro content by 5%. 99% of cases will be fixed by either the glow plug or new fuel. But in rare circumstances, a higher nitro content may be necessary.
My engine wonât start. Itâs like the starter battery is dead because the engine wonât turn over. Sometimes itâll go a little bit but it gets stuck. It wonât even turn over with the glow plug taken out!!!
Donât worry! This is perfectly normal, especially on Traxxas vehicles equipped with ez-start electric starters. The reason for it is the high compression nature of our small 2-stroke engines. The best plan of action to rectify this situation is to simply heat the engine up by shooting it with a heat gun (or hairdryer if you donât have a heat gun available) until it is heated up to about 100-120 degrees. This is very uncomfortable to touch with the fingers (for most people anyway). This loosens up the compression just a smidge so that the piston may more easily move within the sleeve inside the engine.
*Note: Donât melt your fuel tank ď
Got a new engine installed and now when I start it, it runs off and I have to hold the brakes to keep it from going. Whatâs wrong?
Check and make sure your linkage isnât forcing the throttle open with the throttle trigger on your radio at neutral, and make adjustments as necessary to fix the problem. Make sure your trims are centered also. If not, be sure that simply moving your trims donât make the car stop trying to run away.
Another mechanical cause of this can be a worn out clutch and/or bad bearings. Break-in is especially hard on clutches and bearings due to the excess slipping which causes lots of heat build-up. If your clutch has melted or the spring has stretched, the clutch will not disengage properly and will keep the car trying to move even at idle.
Otherwise, you may have a simple tuning issue. The idle may simply be too high causing the clutch to be partially engaged which will make your car try to run off.
My engine is hydrolocked (Flooded). How do I get it unlocked?
The easiest way to remove fuel from a hydrolocked engine is to first remove the glowplug from the engine. Next, turn the entire vehicle upside-down and activate the starter. Either pull the cord or run your electric starter until raw fuel stops pouring out of the engine. This will probably make a mess. After this, reinstall the glow plug, reconnect the starter glow plug wire (if necessary), and try to start the engine again.
My engine is flooded but still turns over with the starter hooked up. Can I get it running without pulling out the glow plug?
A nifty trick in this situation is to simply pinch the fuel line and attempt to start the engine. It may take a few seconds, but the engine will usually fire up and run. Once you hear the idle starting to climb, let go of the fuel line and drive your car.
This tip can also be used to finish flushing out the excess fuel after de-flooding the combustion chamber, since there may still be some fuel residing inside the bottom of the crank case that wonât come out when turning the engine over upside-down.
My engine will not draw fuel! My needles are at factory settings but it wonât pull fuel into the carburetor.
You may be too lean. Check your needle setting. If youâre not around that 3-4 turn mark, reset it to the factory setting and try again. Otherwise, you may have a blocked needle. A nice tip for this situation is to first check your main needle setting. Remember where it is and remove the needle itself (just the part that you can remove with a flat head screwdriver. Not the entire assembly). After you have the needle out, place your finger over the exhaust stinger and activate your starter. Fuel should shoot out of the needle (makes a bit of a mess). Place the needle back into the housing where it was, and try to restart.
If this doesnât work, or fuel wonât run out of the needle with the above tip, you may have an air leak in the exhaust. Fix any leaks and your engine should draw fuel.
My engine will idle decent if I keep the vehicle off the ground or if I donât try to stop it from rolling. It wants to keep rolling if on the ground and will die if I stop it.
The most common cause of this situation is either a locked clutch or seized clutch bearings. Try to spin the spur gear in both directions (forward and reverse). If you feel excessive resistance (make sure your brakes arenât engaged) and your engine is trying to turn over with the rotation of the clutch bell, take your clutchbell off and make sure your clutch/bearings are in good shape. 99% of the time, they will need replacing if youâve read this far.
My engine idles if I leave the glow plug igniter on it, or if I hold down the button on my starter (ez start) but if I take the igniter off or let go of the button, the engine will die almost instantly.
Most of the time, this is caused by a rich mixture setting, an engine that's just not up to operating temperature yet, or a burnt out glow plug. Most commonly, the settings are just too rich. Leaning out the bottom end will fix this most of the time. If it doesn't seem to help, put the needle back where it was originally and try a new glow plug.
My car is in front of my house still running. How do I shut the engine off!?!?!?!?!
Placing your finger over the exhaust stinger is probably the most common way to shut off a nitro engine. This has its ups and downs though. Itâs easiest and quickest to do, but can also cause the engine to flood, thus making the next restart more difficult. You may also notice that the end of the pipe stinger may be hot.
Another popular way to stop a nitro engine is to smack the flywheel from underneath with something. I see many people use their finger, but this can be dangerous; especially if you miss and donât hit it hard enough. It can cause burns. Other objects like your shoe or a screwdriver work very well, and it doesnât flood your engine
Pinching the fuel line is another good way to shut off your engine, especially if you are done running for the day and want to pick it up again in the morning. This will cause most of the fuel to be burnt out of the engine, but is still no replacement for burning the tank dry and using after run oil. The engine may require priming on the next restart. This is normal.
Which is worse? Too rich or too lean?
Overly lean running is MUCH worse than overly rich running. Lean running deprives your engine of oil as well as causing excessive heat build-up; both of which will dramatically shorten the life span of your engine. An overly rich setting will cause the engine to wear slightly quicker, but if you always run it equally rich, it will last just as long as if you were to have it at the optimum setting.
How do I reset my needles to the factory settings?
Screw the top end needle in till it stops. DO NOT tighten it down an âextra 1/8 of a turnâ or anything like that. You can break it if you torque it down at all. After that, count FULL ROTATIONS. DO NOT mistake a half rotation for a full rotation. It is very easy to do as a beginner, and I once did it myself. However, if you do, youâll be at 2 turns out instead of 4, which is the difference between an engine that is slightly rich and an engine that is so lean it may not even start. As for the bottom end, do the same if your manual recommends a setting from a closed position.
If youâve lost your manual, most newer engines will run with 4 turns out from closed on top-end and a bottom end needle that is flush with the end of the arm it is screwed into.
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RE: Nitro Guide and FAQs - 
. Curiously, although the piston itself looked brand new, the chrome liner was also running in beautifully. I'll keep this short because if anyone's interested in the full test with photos I have it in the engines forum at 
