Old Yamaha CG50 Jog - top Speed gone down!!

Skunky

Too old to die young
Yamaha CG50 Jog - mild modifications??

Hi everyone!
This is my first posting, I have just joined today.

My winter project has been a Yamaha CG50 Jog - air cooled 1995 model.
Bought it from E-Bay and took the panels off when I got home, WHAT A MESS!!
So, 4 months later its back on the road, rebuilt and now done 80 miles with the following changed from standard -

RMS 49cc piston & cylinder kit. ( Cheap, but probably less restrictive than a standard Yamaha one).
Technigas standard type exhaust but derestricted.
Mallossi red foam filter in derestricted airbox.
Carb jetted up 2 sizes & needle lifted up 1 notch.
Standard Variator, with washer removed between discs.
But -
I can't get passed 60kmph/38mph!!

The engine revs cleanly, but the scoot reaches 38mph and thats as fast as it goes. There is still more "throttle" to be had, i.e a bit more rpm, but no more speed??

I had 5g rollers (it wants to pull wheelies with these in) fitted so I upgraded to 6g, my local scooter tuner advised that I would get more top speed, but the opposite happened, I lost 2mph!!

Has anybody any ideas what i can do please.

Regards,

Frustrated, Born Again Biker!!!
:?
 
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tiba_karotsu

OVERREV TUNING
can you post a pic of the scooter? is it a japanese market scooter? if so it has a 60kmh limit built in the CDI you'll need to get past that before you can go faster. you'll need a derestricted CDI, aftermarket vario, rollers & kevlar belt & it should hit 80kmh no problem, you should have bought a 70cc kit instead of the 50cc kit, you can still run it with the stock carb & exhaust with minimal or no carb tuning.

you lost speed when you installed heavier rollers bcoz you lost some revs up top, 50cc's need to revved high to make power hence the need for lighter rollers. heavier rollers work only when you got more torque, that is something a 70cc can only give.
 

Skunky

Too old to die young
Slow Jog!

Hi Tiba,
Thanks for the reply.
The Jog is a UK - Artistic spec one.

I decided to keep to 50cc as my 16yr old daughter could use the scooter for transport.
(It is illegal in the uk to ride any motorbike over 50cc at 16 years old).

The standard roller weights on the jog are 6.5g. So the 6g ones in theory, should have given me more top speed than the 5g ones i fitted.

I wonder if changing to 4.5g rollers would do anything to the top speed, i know it would accellerate quicker but it should lose top speed with lighter rollers?

Maybe the standard vario is at its closest point at the max revs and an aftermarket one has a slightly larger diameter to change the gearing?

Anyone else had anything like this please??
:?



 

srtimmy

New Member
Maybe you should get a aftermarket variator or like tiba said get a 70cc kit. But you like to keep it 50cc so maybe a aftermarket variator is the answer hope this helps a little bit.
 

tiba_karotsu

OVERREV TUNING
Hi Tiba,
Thanks for the reply.
The Jog is a UK - Artistic spec one.

I decided to keep to 50cc as my 16yr old daughter could use the scooter for transport.
(It is illegal in the uk to ride any motorbike over 50cc at 16 years old).

The standard roller weights on the jog are 6.5g. So the 6g ones in theory, should have given me more top speed than the 5g ones i fitted.

I wonder if changing to 4.5g rollers would do anything to the top speed, i know it would accellerate quicker but it should lose top speed with lighter rollers?

Maybe the standard vario is at its closest point at the max revs and an aftermarket one has a slightly larger diameter to change the gearing?

Anyone else had anything like this please??
:?




the stock vario is very limited in it's range so the fist thing i would do is to buy a variator kit like the malossi, that should increase your topspeed by widening the range of your transmission.

do you have the model with a front drum brake? is it a gray import from japan or a uk domestic model? if you put the bike on a stand & rev the shyt out if it does it sound like it's burbling? your poweband is limited by the rpms you engine can achieve & with the stock cdi i think it's limited to around 8K to 10K rpm so for the Jogs that came from japan we replace the cdi with unrestricted units & that gives an extra 10 to 15kmh topspeed.
 

Skunky

Too old to die young
UK Spec!

Hi Guys,
Yeah the Jog is a Uk Spec model with a front drum brake.

Gonna have to try revving it out on the centre stand when it is run in a bit more and when the neighbours are out !!!

Probably will try a new variator assembly - do the Mallossi or Polinis come with the outer pulley in the kit as well as the back weighted pulley??

If the cdi is restricted, I have heard that if the red wire is disconnected, it raises the rpm??

Do these engines go BANG! easily if rpm is raised??

Thanks for the replies.
 
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