Yamaha Aerox rev problem help ASAP

Hi guys I have a Yamaha Aerox 2010 model was running fine I rebuilt the engine I replaced the standard cylinder and piston with a malossi street race 50cc kit
And added a Leo Vinci exhaust zx
Also upjetted by 10% has 3.5 gram rollers
I am
Lost for some reason it has no power at all until I hit 40mph then the bike goes nuts all the way to 70/75 mph but I can only hit 40mph on a slight hill the bike just won't rev high enough for some reason it's driving me crazy.
No power band until 40mph and acceleration is embarrassing and the new bore has 7 ports instead of 5 really confused I have attached a photo of the cylinder kit below

 

I'd say that because your cylinder kit produces its power higher up the rev range, you'll need to put slightly stiffer clutch springs in to allow the bike to rev more before it engages. if it feels flat from pulling away this is usually the cause. if it goes flat after pulling away it could be the rollers are too heavy, i can't remember what weights the minarelli engines run as standard. keep an eye on your plug colour for jetting, chocolate brown is about right but i'd say you have a gearing setup issue.

 

I reckon you need heavier rollers, as the 3.5g ones won't generate ebough centrifugal force to keep the variator pulley closed on a slight incline as the contra spring kicks in. I would buy a roller kit and maybe see what difference 5g and 7g rollers make. If you haven't upgraded the crank to a 12mm one, I'd advise heavier rollers anyway, purely for the sake of the longevity of the crank.

My 'Speedtrek' TKR runs 8.5 gram rollers, is Stage 1 tuned and can easily hit 10k RPM on a mild incline. With the Yasuni Z pipe on it, the engine could hit 13k RPM and on a 10mm crank, that's not healthy in the long term. My bike runs a rev counter so I have seen this.

 

If I put heavier rollers in the acceleration is worse as I have tried malossi 5g rollers
I think it might be a clutch problem

 

The plug colour is perfect and I also think the same gearing issue but a friend of mine is convinced It's a carb issue or I need to upgrade to a 17.5 mil carb
To be honest I don't think it's anything to do with the carb

 

Maybe you need a stronger contra spring, to push the clutch pulley closed quicker on inclines. That, or your clutch is possibly slipping a bit.

 

On payday I am going to order the full polini kit with the springs rollers and the contra spring and hope that works thank for the advice guys great help

 

Has anyone got a 17.5 mil carb for sale ?

 

Just a reply I finally got some malossi red clutch springs and a stronger contra Spring
The acceleration is worse but now at 30mph the power band kicks in was at 40mph

 

And also1st start in the morning it pulls away like a rocket once then after that I have to push off with my foot

 

Overfuelling then. Down jet slightly or try dropping carb needle a notch.worth checking that your choke isn't sticking on too.

 

Thank you for the reply
I played with the carb needle dropped it half way and to the bottom just made it worse.
Also I tried it with the standard jet and up jetted by 10% and the plug is burning fine brown colour.
Also tried it with the choke plugged in and unplugged just about give up with this bike
Also got some carbon malossi reeds took the bike apart n need a special tool to get into the reed block

 

Check for evidence of fuel/oil mixture getting into the transmission or ignition stator sides of the engine. When you rebuilt the engine, did you fit new crankcase oil seals? Worn crankcase seals can give all sorts of weird symptoms.

 

I didn't change the crank gaze oil deals just the base gasket and head gasket what come with the kit I will have to double check what you have written just it was working fine before I fitted this kit it did recommend a 17.5 mil carb for use with this malossi kit so I have ordered one hope that sorts it out or I will sell the bloody thing

 

The original worn seals may have been borderline on the original kit and the uprated sports cylinder kit may have tipped them over the edge. They don't last forever and at least they are cheap.

 

I think this is not a carb problem! CVT!

 

I am not sure what the problem is but 1st start in the morning when the choke is on it has 0 faults
When the choke turns its self off is when I loose acceleration
I just need to order a manual choke for my carb to test it

 

The mixture is richer when the choke is on and weakens off as the choke turns off. Your fuel mix could be just about right at cold start, but goes seriously weak as either fuel mixture leaks out or air gets drawn in via the worn crank seals. I stand by my diagnosis of knackered crank seals.

 

I changed the variator to a polini one and the issue is sorted strange

 

Crazy shit