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MOOTTORIVINKKEJÄ BY JOSH CYRUL

Once a nitro engine has been run through several tanks of break-in it’s finally time to tune the engine for racing. Here is the following procedure that I go through after I have broken an engine in or when I have arrived at a new track where the weather and air conditions are different from where I have previously used the engine.

First off, I raise the idle about ¼ a turn from where it was previously run. This is just to keep the engine from stalling when I start going through my routine. Next, I will fire up the engine “blipping” the throttle a few times until the engine is up to a reasonable temperature. Some where in the 150 degrees range. Now, I will richen the top end up a full turn. Holding the carburetor wide open I will continue to richen it up till the engine nearly stalls. If it does stall that is ok, just lean the engine back in slightly so you can get it to re-start. My reason for doing this?? This helps flush out any dirt or residue (or after run oil) out of the carb and engine. Now that things are cleaned out we can begin to tune the engine to race trim.

First off, I’ll set the bottom end. To do this I will listen to the idle. If the idle slows down and the engine stalls I will lean out the bottom end needle. If the idle speeds up then I will richen up the bottom end needle. Usually, I set my engines to idle at least 1 minute before the idle slows enough to stall the engine. Once the idle stays consistent for 1 minute I will lower the idle as much as possible until it stalls. From that point I will raise it back about 1/8 of a turn. The lower you can set the idle means lower engine temperatures, better fuel mileage and better operation of your clutch since a high rpm idle can slightly engage the clutch causing excessive heat and wear. Overall, your engine should idle nice and consistent for at least 45+ seconds. I’ve had engines idle for a whole tank when set-up properly!!!

Next it’s time for the fun part! The top end needle, where all that straight away speed and power comes from. This is more of an adjustment for out on the race track but here’s a way to get it close on the bench. I begin by opening the carburetor to full throttle (never for more than 2-3 seconds before returning it back to idle during this leaning out phase). Listen to the engine and lean it out until it sounds like it is achieving a nice clean sound. This is a critical adjustment that will greatly decrease the life of your engine if you get in a hurry here so take your time. Once you get it to where you think it is close you have to make sure that the engine won’t lean bog or hesitate (say after a long straight, hard braking and then hard acceleration to the next corner). Open the carb to full throttle for 2-3 seconds, then close the carb for 2-3 seconds, then back to full throttle for 2-3 seconds. Your engine should rev nice and clean through the 2nd full throttle blast. If it hesitates at all then your engine is too lean and must be richened up on the top end needle.

Most importantly, listen to your engines. A lot of people fall into just watching the smoke that comes from the exhaust and tuning the engines that way. This way is ok but if for some reason you use different fuel (with different oil content or mixtures) it becomes much more difficult to make your engines perform consistently from race to race and in different weather conditions from just the sight of smoke. Learn how your engine sounds and responds to your throttle input. Good luck and have fun!!!

Josh