Mantis II tuning

I just bought a Sundiro Mantis II, and need a little help with tuning:

I've been able to get a nice idle by tuning the carb idle screw, but I get a hesitation or bog when acelerating uphill, to the point that it almost dies. On level ground it's OK but not great aceleration. I've tried tuning another screw (mixture) on the carb but it didn't help much.

Anyone out there have similar experience, and how did you fix it?

BTW, I don't have a dealer to help me, I bought this thing over the internet. Nice scooter, just needs a little tuning.

Thanks for any help....


RE: Mantis II tuning

You need to calibrate the carburettor, not just the throttlestopscrew and airscrew but also the main jet.

1. Turn the airscrew totally inwards and then 1.25 full turns outward, this is the standard airscrew setting. (one full turn is 360 degrees)

2. Set the idle-speed higher by turning the throttlestopscrew inwards, set it on about 3000 rpm.

3. Turn the airscrew until the revs are the highest, this should be very near to the standard setting, no more than 0.25 full turns.

4. Set the throttlestopscrew back to a good idle-speed.

5. Drive a bit, the moped will probably run poor at this time.

6. Stop and kill the engine immediatly and unscrew the sparkplug (carefull, it's hot!)

7. Look at the color of the sparkplug, the color indicates if the mixture is lean or rich. The plug should be koffiebrownish (no milk). If the plug is blackened the mix is too rich. If the plug is lightbrown (maybe even white with burned electrodes) the mix is too lean. If the color is just right the carb is calibrated correctly.

8. Clean the sparkplug and screw it back in. If the plug is damaged or the deposits on it are impossible to remove then replace it for a new one.

9. Open up the carburettor, the copperish screw in the middle with the little hole in it is the main jet. The size of the jet should be stamped into it (not always readable). A bigger jet will make the mixture richer, a smaller jet will make the mix leaner. If the color of the plug is not too far from the color it should be then the jet you need will be no more then 6 sizes smaller or bigger. If the color doesn't even look like coffeebrownish it will be more.

10. Put the carb back together again. Repeat from number 5 until you've got the right jet.

11. Get a new sparkplug.

12. Repeat numbers 1,2,3 and 4

RE: Mantis II tuning

Thanks for the suggestions:

I have accomplished steps 1 thru 8, and indeed the scooter doesn't run too well when accelerating. The sparkplug is light brown/light gray in color; too lean.

That makes sense, since I had the air screw closed to within 0.25 turns of full closed, to get it to accelerate semi-decently.

This weekend I will attempt to get at the carb, which is behind a few plastic panels on this scooter, and look up the main jet size.

I'll try a motorcycle shop to see if they have a few sizes larger.



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