Advanced Engine Tuning Tips

[Plex]

The hardest part of 1/8 scale racing is fine-tuning the engine. You need to learn this on your own. Spend some time, even an entire practice day, developing this skill. Always remember, it never hurts to have the fuel mixture too rich, but never, NEVER let the mixture get too lean.

Basic tuning procedure is as follows:

1 - set the engine�s idle speed up slightly higher than normal
2 - start tuning your engine with the settings too rich
3 - always tune top end first
4 - tune bottom end next
5 - reset idle speed


You tune the engine by measuring the engine�s temperature, and making the required adjustments to make the temperature correct. There are two ways to measure the engine�s temperature:

a) Temperature gauge method: Get the engine up to running temperature, bring the car into the pits and immediately take a temperature reading. Place the temperature gauge directly over the engine, pointed at the glow plug, and take a reading. It�s easier to do if you have a second person to take the readings for you.

b) Spit method: Get the engine up to running temperature, then pull in as quickly as possible and put some spit on the engine�s cylinder head (quickly, so as to not burn your finger). The saliva should just slowly boil off (2 to 3 seconds). It should NOT dance around as if it were on a hot griddle, nor should it lay there and steam. In short, if your spittle will sizzle, it's too hot.

If the engine is too rich, the engine temperature will be colder than desired (and vice versa). If the engine is too lean, the engine temperature will be hotter than desired. Go out on the track with the top end rich. If you have got the mixture set right, there will be heavy smoke from the engine on the straightaway. Run four or five full laps to get the engine up to running temperature before touching the carb. Bring the car in, and take a temperature reading. Start leaning out the top end by turning the adjusting screw only 1/12 turn at a time (picture a clock�s 12 even spaces). Take your time doing the adjusting - don�t be in a hurry. It may take a while. Your goal will be to get the car to just "punch clean" when you come onto the straightaway, which is what it will do when the mixture is set properly. For 1/8 scale cars, you will have the correct mixture when the temperature is about 200 degrees. The 1/10 scale cars run a little hotter, maybe around 250 degrees.

Once you think you have the top end set, run 3 or 4 laps, then stop the car close to you on the track and let it idle for 5 seconds, then "push off". It should have slightly loaded up, but still accelerate quickly. If the engine died before the 5 seconds, check the following:

If the engine seemed to load up and slowly stop, it was probably too rich.

If the engine�s idle speed increased before it stopped, it was probably too lean.

Always run a few laps before testing bottom end and idle. Ron likes his car to idle clean for 5 seconds, but by 6 or 7 seconds his engine loads up when he punches off (heavy smoke with a slight stumble). At this point you may have to re-adjust the engine�s idle speed. If the idle speed is too high, the clutch will not release completely and you will lose "snap" off the corners. If the idle speed is too low, the engine may stall on the starting line, or at the end of the straightaway when you let off the throttle.

Things to Remember:

1 - Never try to tune a cold engine!
2 - Adjust top end first
3 - Always tune from rich to lean. If in doubt, richen it up first.


Your glow plug wire should stay bright like chrome. If it turns dull, or gray, the engine was probably too lean on top or bottom, or both. Note: wire may also distort or be burned up if it�s too lean. If glow wire is still shiny like new, but distorted, you may have to add a 0.004" shim or use a lower percentage of nitro.

Over 99% of all engine complaints are usually related to the tuning of the engine or clutch.

Source: http://www.ofna.com/guide-tune.html