Help need more speed/rpms:

[zbuck]

GY6 72cc engine 4T. I am only getting 6900 rpm's at WOT. Completely stock drive system. Any suggestions/ideas will be greatly appreciated. Thank you, Don B.

[Rebel]

you can play with your roller weights to adjust the functional rmp range.

[theswede]

The 139QMB is designed for a max working rpm of about 7500. Higher rpms than that may very well damage the engine if run for extended periods.
Max torque for the 50cc is some where around 6000-7000rpm (figures differ here in the specs I have).
Possibly the 72cc has its max torque in a different range, maybe some of the engine experts here can comment on this.

I would suggest that if you are able to accelerate on flat, level ground all the way up to max speed @ 6900 rpm then you most likely have enough power to go faster, but are limited by your CVT.
You need to get your drive belt to travel all the way up the front pulley in order to get to the top "gear", without that you can't go faster unless you increase rpm.
An easy way to check if your belt is traveling all the way is to draw a line on the pulley surface itself, from the center to the edge of the pulley. The head out for a short ride, make sure to max out the scoot and then check how much of the line that remains when you get back.
If the belt is using the entire range of the CVT system, all that should remain of the line you drew is a short mark at the very edge of the front pulley.
If you see any more than that, you need heavier weights in the variator to make the belt travel further up.

Hope this made some sense,

Otto

[rob]

You may be able to get an aftermarket variator with a larger diameter or change to the largest diameter tire that will fit and still have clearance , or both for better final drive gearing . Rob

[Rebel]

OK,

it as been a while since I thought about tuning for rpms, if I recall correctly, lighter rollers will need a higher rev to get all the way out.

using a belt that will go to the outer edge of the variator is going to give you a higher final gear ratio, bringing the RPM's down

Using a high performance vairator also give you a higher final gear ratio as well as using a taller tire.

I'm not against getting a higher final drive gear ratio, but to get your RPM's up you need to either lower the gear ratio in some way or get the weights/rollers/sliders adjusted for the rpm range you want.

So now I wait for more input, correct me if you think I'm not getting it right.

If you are wanting more power out of the scooter, you should think about .

1. a high flow air intake, then you'll possibly need to re-jet the carb

2. free flow exhaust

3. tune the variator

4. consider a big bore kit, 72cc

5. consider a performance CDI

6. get the head ported and polished

[zbuck]

Thank you Rebel, Theswede and Rob for your replies. I will check my roller weight and belt travel. Rebel 1,2,4 and 6 done rev limiter removed. Changed back tire from 300-10 to 350-10.

[Rebel]

well, if the rev limiter is gone, you probably don't need a performance CDI, you should have a pretty strong little 72cc as is sits.

[rob]

zbuck ; as theswede said you should be able to push past 6900 rpm if you arent rev limited . All i can suggest is running it at no load to see if your ignnition is breaking down and not letting you past 6900. Warm it up first . In my experience ignition parts dont like heat , and i dont like thinking of taking an engine cold to 8k rpms . If the spark will take you to 8k rpms with no load then the carb becomes the next area I would look at . Check the look of the plug . Did you rejet with the 44% displacement increase ? Any loose vac lines / choke open all the way ? From what we know now ; those two areas strongly suggest themselves to me . I think you should still have plenty of vacuum at 6900 rpm with the bore kit but you might try eliminating the vacuum petcock if you have 1 for testing purposes If your fuel will gravity feed . Rob

[zbuck]

Rebel, yes this scoot is real strong out of the hole and up to 6900 rpms, then just flat lines. No ingtion(sp) miss or carb sputter. Rob, plug looks good a little rich. Had 85 main jet but it was real rich, black soot on plug and exhaust pipe. Changed to a 79 jet. Only vac line removed, manual petcock. Tested enrichner off the scoot and it is working. Have not checked rpms with no load. Don B.

[Rebel]

What is your speed when you have it going at the 6900 rpms. My point is that if you are going 45 or more, you are probably doing about as good as you can reasonably expect.

[Rebel]

this might be of interest to you.

"racing" variator $29.00 = $15.00 shipping

cgi.ebay.com/ebaymotors/Racing-variator-KIT-Honda-Dio-GY6-50cc-139QMB-_W0QQcmdZViewItemQQhashZitem4cef2d235fQQitemZ330430227295QQptZMotorcyclesQ5fPartsQ5fAccessories

[zbuck]

Rebel, Speed-o-meter is broke. that variator looks interesting, I will check on it. Probalby should get one of those bike speed-o- meters to see how fast I am running. Don B.

[Rebel]

If you look in the how to area we have there are some directions on installing a bicycle speedo on your scooter, it is the cheapest thing to do and can be calibrated to be pretty accurate. Then the high end thing to use iis a Vapotech computer iff you want to go high tech.

bicycle speedo;

scooterrebels.proboards.com/index.cgi?board=otherreadonly&action=display&thread=44

vapotech;

scooterrebels.proboards.com/index.cgi?board=otherreadonly&action=display&thread=590

[zbuck]

Rebel, Thank you for the link. I will go with bike speedo. the vapotech is a bit to pricey for me. Don B.

[jmkjr72]

i would also consider a larger carb on your aplication
you may have reached the point where your carb can't flow enough air for your set up

plus i do know that some companies like kymco have gone to a cdi that you cant completly defeat the rev limiter in the cdi without replacing it