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My 50cc Chinese Scooter GY6 QMB139 hard start when cold, anything below 65 degrees F. Last spring when I got it I had nothing but trouble, fixed the following and it ran perfect all summer until it got cold. 4 stroke. Cleaned carb (many times) bypassed the fuel petcock with a shutoff the screws on the top of carb that cover the diaphram were too short that caused air, fixed that with longer screws replaced the intake manifold, (had a tear) I always use high octane gas with a cap of that blue enzyme stuff

When the scooter is warmed up it runs great but I need to stay on the throttle for 20 minutes cause it will stall at idle as well. Today was 55 degrees out, when I got it running good I went to the store, 15 minutes it was not running, started and ran good for 1/2 mile then bogged down and stalled at my 1st light. Takes 20 seconds to start and it takes right off but will do the same until its warm. Usually I drive it 2 miles on back streets until its warm because it will stall 3-5 times

Robin Kimball
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It depends on the oil that you use on your scooter, If you are using heavy oil then the cold start is going to be a problem, I have a 150 cc Gy6, I use lighter oil like 5w-40 and I had no problem, but if you are using any other oil that has higher viscosity than 5w-40, you better switch back to the 5w-40.

The manual suggests 75w but most people use 5w-40. I use the same and never had any problem, my scooter has about 5000 miles. So save the heavier oil for summers and lighter oil for the winters.

kasey
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