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gitsum · 03-19-2014, 01:29 AM

Most generic GY6 150cc scooter engines are tuned to make their best horsepower around 7000 rpms and peak torque about 1000 rpm's lower. There are exceptions and variations of course, but the majority will fall into this profile.

Tune your variator with weights (I prefer sliders) that allow the engine to rev between 6500 - 6750 rpms during WOT acceleration. Ideally you want to reach maximum speed on level ground around 7000 rpms, 7500 at the maximum. If you are revving the engine above 7000-7500 rpms at top speed but staying at 6500 - 6750 rpms during acceleration, you need taller gearing. This can be done by using a larger diameter rear tire, shaving the variator boss (you may need to adjust the variator weights slightly lighter to maintain optimum engine speed during acceleration), an aftermarket variator, or a taller gear set in the transmission.

I have three parameters I strictly adhere to for running an air-cooled GY6 in regards to reliability and longevity.

1. At sustained cruising speeds the rpm's should not exceed 7000.
2. The engine cylinder temps remain under 350 f, 375 f for a short period of time (like less than 10 minutes)
if climbing a long grade.
3. If pushing the scooter regularly at higher speeds/temps, change the engine oil every 500 miles (gear oil 1500 miles) and keep the valve clearances in spec. For a Taiwanese or Japanese air-cooled scooter valve checks/adjustments every 2500 miles or so, for a Chinese scooter I would check more like at 1500 miles.

Most carbureted air-cooled GY6 scooters are tuned almost too lean to pass emissions. The carb needs to be properly tuned and jetted, and should have an air/fuel (pilot) screw for adjustment. On some carbs this is blocked off (you can remove the blockage). There are a few carbs that don't even have an air/fuel adjustment screw, I would suggest replacing it with one that does.

I don't worry so much about sustaining WOT for high speed cruising as I do engine temps.

Following these guidelines I fully expect my Taiwanese scooter to last a long time without premature engine wear or an engine failure. The top end should go at least 25,000 miles, perhaps as many as 50,000 miles.

03-19-2014, 01:29 AM	#2
gitsum Join Date: Jun 2010 Location: southern Arizona Posts: 37	Most generic GY6 150cc scooter engines are tuned to make their best horsepower around 7000 rpms and peak torque about 1000 rpm's lower. There are exceptions and variations of course, but the majority will fall into this profile. Tune your variator with weights (I prefer sliders) that allow the engine to rev between 6500 - 6750 rpms during WOT acceleration. Ideally you want to reach maximum speed on level ground around 7000 rpms, 7500 at the maximum. If you are revving the engine above 7000-7500 rpms at top speed but staying at 6500 - 6750 rpms during acceleration, you need taller gearing. This can be done by using a larger diameter rear tire, shaving the variator boss (you may need to adjust the variator weights slightly lighter to maintain optimum engine speed during acceleration), an aftermarket variator, or a taller gear set in the transmission. I have three parameters I strictly adhere to for running an air-cooled GY6 in regards to reliability and longevity. 1. At sustained cruising speeds the rpm's should not exceed 7000. 2. The engine cylinder temps remain under 350 f, 375 f for a short period of time (like less than 10 minutes) if climbing a long grade. 3. If pushing the scooter regularly at higher speeds/temps, change the engine oil every 500 miles (gear oil 1500 miles) and keep the valve clearances in spec. For a Taiwanese or Japanese air-cooled scooter valve checks/adjustments every 2500 miles or so, for a Chinese scooter I would check more like at 1500 miles. Most carbureted air-cooled GY6 scooters are tuned almost too lean to pass emissions. The carb needs to be properly tuned and jetted, and should have an air/fuel (pilot) screw for adjustment. On some carbs this is blocked off (you can remove the blockage). There are a few carbs that don't even have an air/fuel adjustment screw, I would suggest replacing it with one that does. I don't worry so much about sustaining WOT for high speed cruising as I do engine temps. Following these guidelines I fully expect my Taiwanese scooter to last a long time without premature engine wear or an engine failure. The top end should go at least 25,000 miles, perhaps as many as 50,000 miles.
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