RPM's at 20MPH By inca32 (Read 1,693 times)

[inca32]

I have a new (180 miles) Sunny 50QT -4 scooter. Starts and idles great. It bogs a little but I think that is because of the sealed carburetor. It tops out at 6400 RPM's 35 MPH but takes some time to get their. What i notice is that I am consistently around the 6000 RPM range under normal driving of 18-20 MPH and I usually need to run it up to 6000 RPMS then back off to 5500 to maintain 20 MPH. Is this normal or am I running at the top end of the range a lot?

[sprocket]

Most GY6 engines red line at 7500 rpm so you are well under...but the 7500 figure is rather arbitrary...

Maybe want to get more miles on it before you are running these rpms.. at least vary the rpms so, you get the rings to seat...

[Alleyoop]

Your doing good, at 6400 rpms and once you break it in a little more you can bump up the rpms another 500-600 and you will get a little more top end to boot. I like to run around 7000 rpms the max and control the speed with weights. If what you mean the carb is sealed is that the FUEL RATIO screw is plugged, you can drill the plug out and get at the screw behind it.

MOST will have the screw behind it but there are a few that do not. BUT if there is no screw behind the Plug you should get a new carb with the screw available anyway to get that bogging which will happen with temperature changes.
Alleyoop

[inca32]

Thanks for the feedback. I have another question, the most RPM's I can get at full throtle is 6400 (not that I would run it their at this point) and their ain't no more!
Is their some kind of restriction built in because of the EPA requirements starting in 2011?
The carburator even has rivets in place of screws so it can't be rejeted.

[jct842]

As far as the carb goes I think I saw on one of the forums instructions for removing rivets and tapping for screws. I doubt if any one would have much trouble removing the rivets so finding the tread probably isn't that big of a deal. Also I am told the replacement carbs come with screws so if you did mess up, a new 50cc carb is not very expensive.

[sprocket]

They aren't rivets they are headless screws... you need to cut a slot in them with a cut-off wheel on a dremil tool and unscrew them..or drill a hole in them and use a small easy-out...

On a 50cc they probably have a restriction washer in the variator and they may have a RPM restricted CDI

[inca32]

I think I will just replace the carb. How would I find the RPM restriction?

[Alleyoop]

Yes I think it is wise to just replace the carb they are cheap Then you can mess with the other carb get the cut off screws out and drill the plug out and see if the Fuel Ratio screw is behind the plug. If it is then you get screws for the bowl and you will have a good Spare Carb.

If it only goes to 6400 rpms it could also be HEAVY weights in your variator that is keeping the rpms down as well OR it could be the CDI.

But I think if it was the CDI that is restricted that the rpms would go higher and then when they reach the Restricted LIMIT the rpms will drop on you.

So the first thing I would do is check the Weights in the Variator and also see if there is a RESTRICTED WASHER inbetween the Front pulley to limit the top end speed. So I would take the CVT cover off and take the Variator off and weigh the weights. If you do not have a small Digtial scale that weighs in Grams take it to a post office and ask them to weigh one of them for you.

Take pictures when you do this After taking the CVT cover off and take pictures of your Variator when you take if off . This way you know how things will go back and also can post your pictures on here if you need any help.
Alleyoop

[sprocket]

Variator nut can be a real bear to get off.. invest in a cheap impact wrench.. makes the job a breeze...

[aziz1137]

I have a dongfang stg200. It has a 170cc engine and i can get 53 max mph at 6400 rpm. Slightly down hill i can hit 59mph at 6800rpm but no higher. It has a new belt clean stock clutch but the varator needs a little tlc. The rollers are flat spotted and it rattles like mad. The engine creeps me out i change the oil 5 times already almost every mounth haha sounds crazy i know but i found barring size bits of metal maybe a bit smaller there were three of them the bike is only 4 mounth old. I took the varatar off an listen to the engine and it sounds damn good no noise no knocking no ticking just smooth. The only noise i hear is when i take off an heavy on throttle about half an ill hear this rattling crackling sound every time. Im not sure what it is. I checked the valvs an the intake was 004 an exhaust was 003. Last problem i have is hard starting even when hot. I have to hold the start button till it gets going. Some times i dont even have that problem it will pop right off. Compresion seems strong i did the finger test an it blew my finger off the sparkplug hole but i need a gauge to be sure. My kick start want even engauge left me high an dry one day when my battery died