20mph flat out

Hi all, I'm new here but would like some advice please.
I have just picked up a speedfight 50 AC 2003 reg.and can't get it over 20mph tops. It will not rev and the trying to set off on a hill needs a push!
It is a standard 50 with the restrictor plate removed from the variator and a new standard exhaust with the restrictor cone removed from that.
Carb is standard Gurtner with a 72 main jet, also has a new belt and new 8 gram rollers.
I want to use it for commuting to work and back, I am no boy racer being 50+ but I would like to get 40ish out of it to keep up with traffic.
Any help greatly appreciated. I am in Huddersfiels area if you know any good scooter mechanics.
Cheers

 

i would check the carb is clean and is adjusted correctly to begin with. is it smokey at all?

 

Hi, thanks for the reply. I had the carb off and all the jets etc were clean. It is a bit smokey (white ) but I put some 2T oil in the tank so it will probably be that as it also has an oil pump.
The guy I got it off has just fitted a new barrel and piston (50cc ?) why he didn't put a 70 on is beyond me.

 

i dont know about speedfighters but the sound of 8 gram rollers seens Overkill to me

 

Hi antman,
I know 8 gram seems heavy, but 9 gram weights are standard.
I have tried it with 6 gram and no difference, also tried it with 3 x 8gram, again, no difference.
I have fitted a new contra spring today (blue one) still no difference. Also fitted a new carb, cheap and same as the original with a 72 jet, tried a 68 jet as well nothing different. I am waiting for some other jets coming from ebay which are bigger, 74-96 and will give them a go when they arrive.
As I said I only want to get to work and back, but 20 mph is just stupid. It wont even catch a cold.

 

have you checked to see if the previous owner has put the piston in the correct way round ?
also check the reeds to see if there in good condition.

 

Not had the head off yet Paul, but if I do I might just put a 70 kit on and go from there.
tried just about all I can think of and still nothing changes.
If the bigger jets don't work I am stumped.

 

Is the exhaust blocked? Try it by leaving the exhaust nuts loose at the barrel and try it, yes it will be loud but it will tell you either way.

 

Hi Marsh, I dont think the exhaust is blocked, it was only fitted yesterday as the original one had a split in it.

 

does it have a nice blue spark?

i would have a look at the seals on the engine might have a air leak somewhere
also do you have a compression tester? if so it wouldnt hurt to check it

 

I just put the old exhaust back on to see if there was any improvement, made a slight difference but doesn't want to rev past 25 (clock speed).
Spark is good, don't have a compression tester but could borrow one from work maybe. What sort of compression should I be looking for?
Cheers

 

over 100psi is it a pain to start?

 

Starts dead easy on button or kick, and ticks over well, revs ok on the stand but not when riding it?
Before you ask I am about 11 stone

 

to be honest without looking myself it is quite hard to tell whats up with it sorry

 

Well, I am waiting for a set of jets to arrive, hopefully tomorrow so will try a bigger jet and see if this helps any.
Not too hopeful as the scooter is mainly stock apart from the derestrictions.
Thanks for all the suggestions.
I'm sure it must be something simple, but just can't figure it out. Might take the head off and barrel to check the rings etc. Getting pi**ed off with it now.

 

OK head and barrel removed and looks fine, no gasses blowing past the rings, piston looks nice and clean apart from the crown which is black carbon. That could be because I have got oil in the tank as well as pumping. Forgot to check if piston is right way round DOH!
I know the timing would be out if piston is wrong but it ticks over sweet and revs to a decent level on the stand.
but when I sit on it, it struggles to get going.... I mean really struggles to the point that I need to push it. Then on the flat it is barely doing 20 on the clock then it bogs and won't rev, I have to back off just to keep going.

Don't think it's the variator or clutch 'cos, if it was the belt slipping then the engine would rev and speed would stay the same, but the revs just don't build up. I have checked and checked again to make sure that the variator is derestricted and it is.
I am pretty sure that it is a carb issue but am waiting for the jets to arrive.

 

I would suggest that the variator weights are too heavy and the variator is fully open
(closed?) before the engine hits the powerband.

 

Well it's got 8g in now so I will put 6g in and see how we go. I will try anything at the mo.

 

That sounds a good start to me, the Aerox runs 6.5g as standard but most people drop 2g and run 4.5g this allows the engine to reach the powerband and keep it there. The heavier weights throw out too soon bogging the motor below the powerband. When my Aerox was a 50cc I simply fitted a sports exhaust, upjetted 10% fitted a polini variator and 50mph was easilly reached. So something similar should be obtainable with the speedfight.

 

Thanks Mr Bizzle, I would have thought that more than 20 MPH was easily obtainable even with 8gram rollers but struggling to even get off the mark. I will give it a bash tomorrow as weather not good just now and no garage. Even restricted it should be good for 30.
Also watching a sport exhaust on ebay.