Hill Climbing Performance

[jetfixer]

Hi guys. I'm new here and looking for some info on what I can do to get better hill climbing performance from my 50cc Chinese scoot. I put a 72cc big bore kit in it that included re-jetted carb, unlimited CDI, performance cam and coil. Got better top end, but still lackluster hill climbing. Can cruise at 45mph on the straight and level, but as soon as I get on a grade speed drops to around 25-28.

I live in an area that has alot of hills and just want to be able to maintain something close to city speeds (35mph). I have read that maybe some weights or springs may be what I need, but not sure which way to go. Any help/advice would be appreciated.

Thanks

[stepthrutuner]

A stiffer contra or torque-driver spring in the rear clutch/pulley package could help on hills .

[jetfixer]

What size/type spring would help? I'm not familiar with how they are rated. Don't even know what is in it now.

It's a QMB139 engine if that helps.

[stepthrutuner]

The yellow or the red one. Red is stiffest I think. Maybe someone will chime in here. Veerrt?

[Fox]

I bet your weights are worn out (Flat spots)

Changing the weights is the easiest way to gain acceleration. Stock weights are around 7 to 7.5 grams each. If you go lighter on the weights then it'll accelerate and climb hills better. I suggest you try some 4.5 or 5 gram weights. I prefer the Dr. pulley sliding weights myself. They cost a little more than round weights but they last three or four times longer than the standard weights and they provide better down-shifting response when you hit a hill. The 50cc scooters use 16x13 size. I am a big guy (215 lbs.) so I use 4.5 gram weights in my scoot. The 5 gram will be good if you are 170 lbs. or lighter.

In your variator there are 3 little high impact guides that the back plate slides on. If they are worn or broken it'll wear out the variator and it won't down-shift as well on inclines. It's a good idea to order a couple of sets to have on hand because those guides wear out often. You can get them here cheap:

www.partsforscooters.com/151-37-Slide_piece_qmb139

This is a variator in good condition:



This is what happens to the variator when those guides fail:



The other thing you'll need is an impact wrench to loosen the variator nut. I use a cheap 12 volt emergency iompact for changing car tires. They sell them at harbor freight for $30. It's a must-have because the variator guides should be checked at least once every oil change and it runs off the scooter's battery or a car battery/lighter.

www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92349

If you've never had the belt drive cover off you may need to whack it on the back with a rubber mallet after you remove the bolts to break the gasket seal. If the gasket tears it's okay. Just put it back torn or remove it altogether. It's not going to hurt it either way.

Here's a video of a guy changing weights on a 150cc. The procedure is the same pretty much except the 150's use larger weights.



Here's a video of the CVT on a 50cc in action:



Variator:

[Fox]

Sorry, I posted the wrong link to those guides. I fixed it.
www.partsforscooters.com/151-37-Slide_piece_qmb139

[stepthrutuner]

Jetfixer

Here's how you do it, but still don't know which spring would be best for you.

49ccscoot.proboards.com/index.cgi?board=transtech&action=display&thread=356

[jetfixer]

Thanks for the quick responses. The weights should not be worn out. Still less than 500 miles on the scoot. Sounds like 4.5 gram weights (200 lb rider) and yellow or red torque spring. Am I reading it right so far?

[jetfixer]

If I remember correctly, the lighter weights will hurt top end speed. Is that right? If so, how much?

[90GTVert]

The kind of standard rating on torque springs and clutch springs is :

Blue : 1,000RPM (stiff)
Yellow : 1,500RPM (stiffer)
Red : 2,000RPM (stiffest)

Light weights can hurt top speed. If the roller weights are too light they may not be able to overcome the force of the crontra spring. The contra spring and rollers work together or perhaps more accurately work against each other. For example, a set of light rollers may work alright with stock contra spring. Put a stiff contra spring in and the lighter rollers may not be able to fight the contra springs tension enough to get full belt travel. If you put in heavy rollers with a light contra spring the rollers will easily overcome the force of the contra spring and acceleration will suffer as if you are in a higher gear all the time.

[Fox]

Try lighter rollers with a stock spring. I think you'll like the results. I noticed a huge difference on mine. It'll rev higher all the time because the variator will close slower delaying the onset of the higher ratio. You'll burn a little more gas too but the trade off is worth it in my opinion.

[2strokd]

Welcome to the forum ;D! Well put guys! Jmstar that was a detailed great response there buddy! I gotta do a GY6 CVT this weekend.
Same story, guy says it runs out great on the flats, but wont downshift at all for the hills. Im gonna start with lighter rollers first .
One more tip. Only try one change at a time! These cvt trans can be tricky at first. Its best to only change one part at a time. Ex, just try the
the rollers first, or just the torque spring. I wouldnt suggest trying to change them both at once. Might be harder to tune if you do.

[jetfixer]

Once again, thanks for the great answers. Just goes to prove if you look long enough you'll find the right guys with the good answers. I've been researching this thing for a couple of months with no real luck other than some vague references to roller weight and springs. You have all been very helpful.

Looks like lighter weights are the first order of business. Sounds like maybe 4.5 gram 16X13 is what I'm looking for for a 200+ lb rider. Does that sound good?

[90GTVert]

I've had better luck with rollers a bit heavier than that, and I'm nearly 300lbs. A tuning kit might be a good choice than just buying a set of rollers and hoping they do the job. You can use 2 different weights of rollers when staggered to achieve different results. You have 6 tracks in the variator where rollers ride. For example, you could use three 5g rollers and three 6g rollers to achieve 5.5g. 5g, 6g, 5g, 6g, 5g, 6g. The rollers in a tuning kit like the link below aren't the highest quality, but they are OK and it's usually cheaper to buy one of those kits then get the size you need of a better brand than to buy multiple sizes of a good brand.

cgi.ebay.com/ebaymotors/PERFORMANCE-MULTI-WEIGHT-ROLLER-PACK-ELITE-DIO-16X13_W0QQcmdZViewItemQQhashZitem3cabc8e640QQitemZ260580107840QQptZMotorcyclesQ5fPartsQ5fAccessories

[Fox]

Apr 9, 2010 10:13:04 GMT -5 90GTVert said:

I've had better luck with rollers a bit heavier than that, and I'm nearly 300lbs.

Are you talking about a 4 stroke or a two stroke Brent?

I live in the hills too. When I was first attempting to get better acceleration on my 50cc 4T back in the day I removed every other stock roller weight and rode it with three standard weights in there for a few weeks. It revved like crazy and climbed hills great but it lost some top end because it was a little too light. That's when I tried 4 gram Dr. Pulley weights. They worked pretty good and I used that set for a couple of years but they were still just a tad light. Recently I got some 4.5's to replace them with and they are working good.