YY250T - Bogging down at take-off By dekero (Read 1,802 times)

[dekero]

Hey Guys,

I am new to the Board, and new to the world Of Chinese Scoots. I recently picked up a YY250T off of Craigslist. It was nice bike, but the prior owner had not done a great job during the initial assembly. SO I took it upon my self to tear it down and clean everything, tighten all the connections and re assemble.

Good News.. It still works!! and runs well .. for the Most part...

Starts with no problem whatsoever. EVERY TIME.

Idles fine.

the problem is when taking off from a stop.. the bike tends to BOG out and doesn't get up to speed at any real hurry... in fact I have to push off sometimes... and I would say 0-15mph is about a 10 second job...

Once the bike is up to a little speed however it will get up and take off like all is fine... I have had it cruising at 70MPH + while gritting my teeth and holding on for dear life... But it did it..


Don't know where to start... Never took the motor apart during all the cleanup - I did change Spark plugs and oil. and cleaned up the air filter.

I have had friends say its the Carbs air to fuel mix.. but I'm stumped as to why it works well if I let off the Throttle at say 20 MPH and then just floor it, it will take off fast as hell If I'm already moving ... Its like it doesn't like the added torque of having to get going...

ANY HELP would be appreciated... I'm tired of people honking at me when I hit stop lights and take forever to get going again...

Thanks

Dekero

[JR]

A couple of things come to mind and the first is a partially clogged jets. Seems it not getting enough gas until it crosses over the the high speed jet.

The other thing that comes to mind quickly is gummy roller wieghts in the variator. The Chinese use awful grease and if the roller weights are gummed up then they are not moving into the low range and the scooter has to gradually build up speed.

Also you need to check the valves. So even though you've done a lot to help the scooter there is some things left to do and we're here to help you all the way and lastly Welcome to the forum!
JR

[dekero]

JR,

I appreciate the Quick response...!

I just went out and rode it again and I am almost certain the Carb is fine... I do not hear any engine BOG down ... In fact it sounds like its running well..

What I do notice is an Aweful amount of SHAKING when it begins to stop bogging down and starts getting up to speed.. IF I were to guess I would say its feels like the Belt is slipping and slipping until it can finally keep up with the movement and when there is less torque needed, ... Is there an adjustment for the Belt?

Also... If the Rollers you mention are sticking what would be the FIx? is it a job for a novice or should I pay someone to replace them, and maybe check the belt?

I will say I removed the cover during the rebuild and the Belt looked Brand New....

Thanks,

Dekero

[dekero]

Hey... One more thought...

I can also keep my feet on the ground and hold the bike in place as i throttle up.. all the way to full throttle... something tells me thats not right???

the bike shakes and I can feel it trying to push forward, but its weak enough for me to hold it in place...

thought that might help decipher it all... thanks

[JR]

This is most certain a CVT issue and it could be a combination of belt, variator or even the clutch. Belts stretch and wear but most of the time not so bad as to cause this.

First of all here is a video of how the basic CVT system works in motion;

thescooterprofessor.proboards.com/index.cgi?board=genvideo&action=display&thread=388

When you give it throttle and the engine revs up the variator is in low range and it moves into a high range while the clutch simutainously goes into the low range. Both together automatically shift the scooter.

If the weights are stuck in the variator then they won't move and allow this part of the equation to work and the scooter is in high range and a lot of times just like an auto that is taking off in too high of a gear it will shutter and struggle off the line.

Now here's another video.



Even though they are going to another variator and this is a go kart the engine is the same as yours and it shows some of the basics of how to remove it and replace it.

It's not hard and I'm betting this is what's wrong.

JR

[lceel]

I agree that it's most likely the variator. The thing is, that grease mentioned earlier in the thread probably should NOT be there. The variator should be DRY inside - that awful black sticky stuff the Jonway's come with is just wrong. Get some brake cleaner at the Auto Parts Store and clean out the inside of the variator - and that includes the rollers. All you should see inside of a variator is metal and nylon. NO GREASE. You'll need an impact wrench to get the variator off - and while you're at it, take the bell off the clutch, at the back, and check the shoes in the clutch. Make sure they're not glazed. The variator needs a 19mm socket - the clutch needs a 17mm - an impact wrench makes what is otherwise a hard job, easy. I use an 18volt, battery powered wrench - a Ryobi. Works like a charm.

[scootaway]

So what then is the verdict to grease the sliders or not. I am most surprised the video dad does not put some grease on the bush (boss pin) surely any bush needs grease.