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Old 12-13-2016, 04:56 AM   #1 (permalink)
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Poor FE from 150cc gy6 scooter rejetting?

Recently got a Chinese scooter to cut back on my car driving. Payed about 100 usd for it converted. Only issue is outstanding licence its about 3 years behind but it's in every day use.

Im not too impressed with the FE. Im averaging 4.5L/100km or 52mpg my best being 57mpg. See picture of attached log on a fuel app i got.

The drive to work is mostly highway riding about 10 miles each way and city driving about 3 miles. Throttle wide open it maxes at around 55mph but i keep the speed around 45mph. Just don't understand how for a 150cc it is so poor.

Any ideas how to improve this? I recently serviced it and my brother had a look at the spark plug and said it's running way too rich. I'm not too clued up but i know i can play around with the jets. Im at sea level in a warm climate. Standard jet i read up is a 107mm will re jetting to a smaller say around 103 work? Or even smaller. Or is that just what is to be expected from these scooters?

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Old 12-13-2016, 09:58 AM   #2 (permalink)
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Quote:
Originally Posted by Eddie25 View Post
Any ideas how to improve this? I recently serviced it and my brother had a look at the spark plug and said it's running way too rich. I'm not too clued up but i know i can play around with the jets. Im at sea level in a warm climate. Standard jet i read up is a 107mm will re jetting to a smaller say around 103 work? Or even smaller. Or is that just what is to be expected from these scooters?
I think you are on the right track.

If the plug is black, and not tan, it would indicate a richer than optimum overall mixture. Also check that the air filter is clean and the intake is clear. Temporarily running without the air filter would lean the mixture, and may tell you if it will run better if tuned leaner.

Sometimes finding parts for the Chinese engines (carbs) can be challenging, but usually they are a direct copy of one of the more popular brands. Jetting takes some trial and error to get right, but I would expect better number than you are getting so something isn't right.
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Old 12-13-2016, 10:56 AM   #3 (permalink)
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Is it a 2 stroke?
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Old 12-13-2016, 11:43 AM   #4 (permalink)
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If you are living at altitude then there is a good possibility that your scooter has sea level jetting and is thus running too rich at altitude.

Try dropping the needle a couple of notches as this will lean out the mixture at part throttle.
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Old 12-13-2016, 01:34 PM   #5 (permalink)
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If it is a 2 stroke leaning it out gives the engine less oil too.
Frying the engine is the danger of going too lean.
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Old 12-13-2016, 03:23 PM   #6 (permalink)
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Its a 4 stroke. I've got a china clone in my son's gokart. Brake drag perhaps causing it? We have a lot of problems with the spark plug boot tip breaking causing lots of misfires where it can't hold on to the end of the plug.
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Old 12-13-2016, 03:40 PM   #7 (permalink)
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If it is a 2 stroke leaning it out gives the engine less oil too.
Frying the engine is the danger of going too lean.
If it were a 2-stroke it would most likely be oil-injected, so leaning the mixture would not effect the oiling.

Running overly lean will cause problems, but tuning for optimum performance isn't going to make it get less oil than it needs if you have an adequate fuel/oil premix ratio (if it's not oil-injected).

I run 32:1 premix in all of my 2-strokes including my Derbi GPR. It's surprising, but more oil actually will give you more power - up to a point.
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Old 12-13-2016, 03:43 PM   #8 (permalink)
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Originally Posted by cr45 View Post
If you are living at altitude then there is a good possibility that your scooter has sea level jetting and is thus running too rich at altitude.

Try dropping the needle a couple of notches as this will lean out the mixture at part throttle.
That may help, but if he's running 45mph with a scooter that maxes out at 55mph he's running close to wide-open, so it's mostly running on the Main Jet.
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Old 12-14-2016, 02:02 PM   #9 (permalink)
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It's a 4 stroke and I'm at sea level. Went to the local scooter shop to enquire about carb tuning and why im getting such poor FE. He said I'm not getting much worse than he is. They just lack that refinement of the Honda or more known brands. He gave me some tips mostly to stop flooring it.

I do lots of lane splitting in town and when the light turned green i always tried from a safety point of view to excellerate hard to merge into a traffic lane before the other cars catch up. Stopped doing that now and added a vacuum gauge.

Filled up today and got my best so far of 3.9l per 100km. But still far off what i was expecting. Lucky these Chinese scooters in this country have flooded the market so parts are easy to get.

Picture below of it. Used an old helmet visor as bit of a windscreen to deflecte some air a bit better around me. Flaps beneath the handlebars line up perfectly with the front body piece to form a solid barrier. This was to keep my legs dry when it rains as only my bike jacket is waterproof. The air use to funnel through there and wet my knees and crotch
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Last edited by Eddie25; 12-14-2016 at 02:14 PM..
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Old 12-14-2016, 02:34 PM   #10 (permalink)
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I'd still try re-jetting if the plug was anything but a medium-tan color.

For comparison, my 650cc SV get the exact same mpg as your scooter, in town or on the hwy, does a 12-second 1/4mi, and tops out about 125 mph.

That scooter should be able to do a lot better - no matter how you ride it.

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