One of the most common questions we hear is How do I tune my engine? Here are some great tips we have picked up over the years to make you an expert engine tuner. But remember, engine tuning is part science and part art. You need to practice and listen to your engine to get it right.
First, Break it in Right
Every engine comes with break in instructions. Because every manufacturer is different, you should always follow the instructions from the manufacturer, but there are some similarities in all break-in procedures.
During the break-in, the engine must be heat-cycled properly to wear-in the various engine parts. Heat-cycling is the heating and cooling of the engine to get the internal parts wearing together. It is critical that you heat the engine as close to the racing temperature as possible without overheating. Typically, this will be anywhere from 175 – 220 degrees. Get yourself a heat gun if you don’t already have one.
Remember, to ensure that the internal parts are wearing to each other properly; you should never run the engine at full-throttle during the break in process.
After the Break In
It is important to always adjust the high speed needle first.
Setting the high-speed needle will depend on what type of driving you are doing. You should get the temperature up to full running temperature by running the car exactly as you would on the track or parking lot by making 2-3 high speed runs.
Your high speed needle setting should be set to maximize the engine performance for your particular track configuration. Short, tight tracks tend to require settings slightly on the lean side for maximum power through the corners. But long, high speed tracks might need a slightly rich high speed needle setting.
Start by leaning the needle just until the engine sounds as if it’s going to cut out from lack of fuel. This is referred to as the engine’s rpm sweet spot.
But don’t leave the needle at this spot; richen it by at least a quarter-turn from optimum power. This provides ample high-end power with enough fuel to prevent overheating.
Remember, the high end needle affects the fuel mixture above ½ throttle. It should be adjusted so the engine is running about 300-400 rpm shy of the max lean rpm at full throttle.
Adjusting the Low-Speed Needle
After you have adjusted the high-speed needle, it is time to adjust the low-speed needle. It’s important to note that your engine spends most of it’s time in the low to mid range which is affected by the low-speed needle. The low-speed needle affects the fuel mixture below ½ throttle for most engines and you use it to adjust the idle and the transition from idle to full throttle.
Also, remember that an overly lean low-speed needle setting can cause an overheated engine.
There are many opinions on how to set the low speed needle. One common way is the “pinch test”. Run the engine to get it warm, then stop and pinch the fuel line. If you notice that the rpm rises instantly, the needle is too lean. If your engine won’t allow the low speed needle to be set rich enough to pass the pinch test, using a hotter glow plug should allow for a richer low-speed setting.
Another method is to run the car at top speed for a few minutes. When you stop, if the idle drops almost instantly, your low end needle is leaned just right.
A properly tuned engine should load up with excess fuel when idling for more than 7 to 10 seconds. If your engine idles all day without loading up, the low end is too lean.
If you set the low-speed idle right, you should be able to pull strongly off the line without hesitation after sitting for about 10 seconds.
Check the deceleration too. If the engine’s rpm drops uncharacteristically low, the low-speed setting is too rich and if it seems to keep revving, it is too lean.
Setting the Idle
The last thing to do is set the idle. The idle-stop screw controls the carburetor’s opening when the throttle is set to neutral. Setting the idle should only be done after you have set the high and low speed needles.
Adjust the idle only after the engine has been thoroughly warmed up.
The ideal setting is fast enough to prevent a stall but not so fast that the clutch engages
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