Extremely Confused With Tuning

Hi guys I hope you can help me, I'm 17 and I've just bought a Speedfight 2 50 AC. Atm its sitting in the garden waiting to be insured and I want to tune it all up so its all done and ready once it's on the road. It's fully de-restricted and has a Leo Vince ZX exhaust fitted. Just messing around in the garden I've noticed it revs quite high before moving. I want to tune this bike but am confused on what size jet should be in the carb, what roller weights to be using and what clutch springs to use. I've been told that the carb should be up jetted (size is not stamped on jet) and rollers changed for the exhaust that was fitted by I have no clue what has been done to this bike and need a little help!!

 

OK, I have a TKR2 which has the same engine as the SF2, although mine looks a little different now, as you can tell from my avatar (look up 'Project Speedtrek' to see it in better pictures). The standard main jet on your carb is a 72, so you need a 76 jet if you are on the standard air filter and maybe an 80 jet if you are on a sports air filter. My TKR2 is on an 82 jet that seems to suit it, but setups vary from bike to bike.

Rollers wise, you are probably on the light side with the rollers and the SF2 has 15x13mm, 9 gram weights as standard. The engine has to spin up the variator enough to grab the belt before it can start to throw the clutch out and move the bike. I would try slightly heavier roller weights, say 10 grams and see what difference that makes. My bike has 9.5 gram rollers and could use some that are a little heavier if I am being honest.

Leave the clutch springs alone until you get the take-off you want from the variator, as stronger springs in the clutch will make the problem worse!

 

Thanks Merlin!!! Your info is a great help, now that I have an idea of the setup I need I have further questions
My bike has a Malossi E5 air filter fitted so i need a jet somewhere around 80, correct? And as for the rollers im gonna order a pack tomorrow but ive been told conflicting information :/ from what ive read with a sports exhaust you need lighter rollers not heavier? I dont have a clue tbh and I trust you guys know what your talking about

Also i Know on the ZX pipes there is a restrictor washer welded into the end. Havent had a chance to see if mines been removed yet but if it hasnt will the jetting and roller weights be different to the ones you've said?

 

Also where did you get your rev counter and how much!!!!

 

OK, on the topic of rollers, things get complicated when you try to explain how they work, so stay with me here. Rollers work on the principle of centrifugal force, in that they need to be thrown out in their tracks due to centrifugal force caused by the crank spinning. The more rotation speed, the more centrifugal force. OK so far?

Right. The centrifugal force gets transferred into actual force that pushes the variator pulley out until it grips the belt and starts to drive the clutch. If you put lighter rollers in, the crank has to spin faster to generate the same amount of force on the rollers to push the pulley out. This can be bad news if you are on the standard crank, as you might exceed the redline for the crank and break the conrod, wrecking the engine. This is why I said go for slightly heavier rollers, as you don't know if the bike has a standard or aftermarket crank, so it's best to use heavier rollers to engage the belt a little earlier and limit the maximum revs.

Lighter rollers = higher revs and potentially faster take-off, but can be unsafe if you exceed the redline.
Heavier rollers = slightly slower take-off, but is safe for the crank.

As for your jet, I'd get an 80 and an 82 jet and try the 82 first. If the bike 'bogs down' slightly on pulling away, then try the 80 jet. It's always best to start high and work down, as you are starting off with a richer mixture and avoiding the risk of seizing the engine due to a lean mix.

If the exhaust has a washer welded into the end you can just remove it. The ZX exhaust also has a tube inside the muffler that needs to be opened out at the end to fully destrict it. There are videos on this subject on a certain scooter parts side starting with Ped.

My rev counter is a cheap Chinese one that I built into the Speedfight clocks. I ripped out the innards from the chrome housing that the Chinese one came in and just used the guts of it. I had a spare set of Speedfight clocks so I used the petrol gauge needle from the other clocks to make the rev counter match the others. The black fascias were made by me in Photoshop and laminated, there's a picture of them on here somewhere. It works well for such a cheap clock.

 

Thanks Merlin, the roller situation makes a bit more sense now!!!
As for the exhaust, if it has not been de-resricted (washer still there) will I have to use different roller weights and jet sizes to the ones you've stated or are they still correct for a restricted ZX ?

 

Take the spark plug out and have a look at the ceramic insulator in the middle. If it's light brown, then the mixture is OK. If the insulator is light grey or white, then the mixture is weak and you need a bigger jet size. The exhaust note will also sound very 'tinny' and 'WAAAAA' in note if the mixture is weak (hard to describe in print, but you get the idea). If the top end mixture is weak, the bike will also feel 'flat' and strained at the top end.

The jet size is more important if the exhaust has been de-restricted, as the engine can suddenly breathe a lot easier and the change in gas flow can mess up the two-stroke scavenging, making the fuel-air mixture weak.

 

just so you know, speedfights are very revvy engines, as in that revving before it moves off, i suspect the clutches are made of some odd material, they are all like it, lots of revs on pull off from cold, almost red line in fact, it gets better once the clutch has warmed up a bit.... but yeah, merlin is bang on the money, follow what he says and you will be happy

 

Thanks for your help guys, once i get the chance im going to check if the exhaust has been de-restricted. In a way I hope that it hasn't because I dont want too much speed, just enough to get out of dangerous situations, also because I dont wanna be using a big jet because i know that speedfights are sh*t with fuel consumption as it is

 

The good news is that heavier rollers will help the variator to push the belt out faster, helping the bike reach cruising speed a little quicker (useful if you need get yourself out of trouble quickly). It will also be little easier on the clutch in the long term and the fuel consumption will be slightly better. With the Yasuni exhaust on my bike I'm getting about 50 MPG, I reckon the Leo Vince Sito I am going to swap for the Yasuni for will make that a little better.

 

Thanks guys, you've been a big help. Once last question... what clip should the carb needle be on?
I've currently got the needle on the middle clip

 

If your spark plug colour looks OK but your bike still feels a bit 'flat' when you pull away and accelerate, then you can adjust the mid-range mixture by moving the clip on the needle. Moving the clip down a notch makes the mid-range a little richer and might cure a 'flat spot'. You can buy needle kits in the same way that you can get main jet kits, but unless you are into really serious tuning, you don't want to be overloaded by too many options. Most bikes that have had an exhaust and air filter swap can be correctly jetted with a main jet swap and a tweak of the needle height if needed.

One last piece of advice when tuning a bike. Fast, reliable, cheap. Pick any two.

If it's cheap and fast, it won't be reliable. If it's reliable and cheap, it won't be fast. Fast and reliable won't be cheap.