Upjetting? Slow through gears? Need help! :(

[danshacks]

Desperate for someone to help. I own a yamaha aerox 50cc. Pretty standard bike, when i first bought it, it was great. It does 50-55 generally. However, its not running great recently, acceleration is very poor, and inconsistant. Instead of most mopeds, where it is a straight smooth acceleration to top speed, but my bike accelerates poorly, gains power at about 15 then stays at 20 - 35 for about 20 seconds, and the eventually gains more power and gets to about 53 mph. I hear the variator is the gear changing mechanism? Could it be that? Also, I have a stage 6 replica exhaust which i bought, but when i fitted it, my bike wouldnt go over 30mph. But i then discovered, a bike needs to be upjetted to match the exhaust or something? I dont know alot about bikes, but i need to sell it in a month or two as im getting a ktm duke 125. Could anyone tell me, how i would be able to match the carb to the exhaust so that it ran great and performed alot better? Can someone help!

[gavcarter]

You've answered your own question, it needs setting up correctly.
I wouldnt try and mess around with it too much - you'll end up with a big of pile of mis-matched jets, a good few quid shorter and probably still have a bike that doesnt run that well.
If it ran great when you bought it, put the old exhaust back on and sell it like that - no one likes to buy bikes that have been messed around with anyways.

ATB

Gav

[danshacks]

I have got the original exhaust on. It ran fine at first, but i think its running bad now due to age. I havent messed about with it, and i wanted to know, if buying a variator would fix the slow through gears problem. And i need to know how to match to the exhaust? A bigger carb? Upjetting, and how...

[moonzoomer]

Leave the bike standard, it is only 50cc so best left standard , if you want to go quicker buy a bigger bike and retain the reliability.

[gavcarter]

Sorry I misread your first post, i thought you had changed the exhaust.

First thing is to sort out the engine before tackling gearing problems.

Start by fully charging the battery, changing the plug and checking the HT lead. Unscrew the plug cap off the wire its attached to and snip about half a cm off the end of the wire, then screw cap back on, this will ensure the plug cap has a decent connection to a clean piece of wire inside the lead. Clean the air filter and carb also.

If none of this helps look in your manual and adjust the mixture and idle screws on the carb back to standard ( even if you havnt moved them check them to be sure).

If this is the older 2-stroke version MAKE SURE there are no leaks anywhere in your exhaust system.

IF you get the engine running nicely and its still not gearing out quick enough then you need to check a few things before deciding what to do.
Firstly check the belt for excessive wear and replace if needed

If not the belt remove and clean the rollers, check for wear, sticking and weigh them if possible.

Heavier rollers will gear it out faster, lighter will take longer and make the engine rev more readily before increasing the gearing.

Clutch springs control the take off speed and also how fast the clutch engages, standard springs usually use a lower rpm and ease the clutch in, aftermarket usually higher rpm and engage the clutch a bit faster.

The variator spring is something for the rollers to work against, to make sure you always end up in "low gear" as the engine slows down.
The stiffer this is the heavier the rollers will have to be to pull the belt down into the plates and "get a higher gear" - or if left the same weight the rollers have to spin at a faster speed to move the belt into the plates.

Knowing your engine is a good idea before trying to tackle the gearing.

On two strokes the exhaust makes a HUGE difference to the engine, you can go from having max power at 4000rpm to 8-9000rpm just by changing the exhaust so it would be handy to know where your power is before trying to find an "ideal" with the gearing system.

A better description of the engine troubles would encourage more replies, especially from the more knowledgeable of the forum but there is plenty above to think about for now