agility 50 now 70cc low speed

[reg]

Hi all, i bought a used agility 50 with 8k on the clock. soon realised it was way down on the performance of my two strokes ( 33mph) so fitted a 70cc big bore cylinder, new 'top-speed' variator, new belt and an 88 main jet. Top speed is still only 40mph. I have checked the valve clearances, the carb diaphragm for splits, all carb hoses and manifold, camshaft setup, auto choke, unrestricted the cdi,  I cannot come up with any more ideas, guys have i missed something? i sure must have but cant see it. any suggestions will be most welcome.

reg

[blue]

mmmmmmmmmmm you for got the drive bos needs to be repalced with a flat one.
With out the new one your belt will only ride so high on the pulles.

[reg]

Sorry guys i forgot mention that the variator boss is the unrestricted smooth type. I have also checked the rear pulley as sometimes these have a raised section to act as a restrictor. The only thing left for me to suspect is the exhaust. is it possible for an internal baffle to be defective?

reg

[blue]

Do you still have the stock air box or open airfilter. if have the stock box try drilling a few holes in the front side of it. Start with 2 holes and if you need more do one at a time. make the holes about 1/2 inch round.

[blue]

Also you can cut the muffler end off .

[naughty lee]

Mark your inner variatior with ink then take the scoot for a run. Does the belt remove all the ink? Or is there some left towards the outer edge? ( use permanent marker pen ink)

[streido]

Mark your inner variatior with ink then take the scoot for a run. Does the belt remove all the ink? Or is there some left towards the outer edge? ( use permanent marker pen ink)

+1 on that. If it doesnt take off all the marker then your belt may be too short, i could hit 45-48mph on the speedo with my A50 still at 50cc's, over 50mph downhills. Your jetting may be wrong too,  do a plug chop to see if its too rich/lean.

[streido]

[reg]

thanks guys, i am going to try marking the variator pulley as suggested. at 40mph the engine is revving very high. i did a plug chop and found it was running too lean and hot. put a 90 jet in now and its running just about right and a lot cooler. but still only 40 mph. are belts available in longer sizes?

[streido]

I can still hit 45+ on a stock belt no probs. You can run longer belts, 736 Malossi belt worked well for me in the past, but its a kevlar and i dont like kevlar belts myself. Sounds like worn rollers or the rollers may be too light. Or the torque spring is too stiff, stock, 1000rpm or 1500rpm spring works well depending on the rest of the set up, i found a 2000 rpm spring doesnt work no matter what i tried, its just too stiff for a 4t 50cc.

[reg]

Hi all, thanks to you all for the info and help. I ground down the variator boss, drilled three holes in muffler end and removed air box, changed to 6.5g rollers and fitted 1000rpm spring. 46mph anywhere very quickly with a few mph left if its a long straight. Acceleration is loads better too. I think i could still shave a bit more off the boss, i will check later and check the plug. Got a 90 jet in there for now but with no air box i might up it some more. Shortening the boss is like fitting a gear up kit. thanks again guys.

[baddi]

Do you still have the stock air box or open airfilter. if have the stock box try drilling a few holes in the front side of it. Start with 2 holes and if you need more do one at a time. make the holes about 1/2 inch round.

Dont drill holes, just remove the restriction inside it and smoothen out any sharp edges and it is then already so good that the pressure in the intake can reach above ambient at WOT, which means that there is only very little restriction in it and that it is properly tuned in length and diameter to 50cc and 6500-8000 rpm. At rpm below and above this the pressure is just ambient or insignificantly below.

The restriction is placed where the white sealing is on the picture and will have to be cut or drilled out.

[reg]

Thanks for the air box tip baddi, its now much quieter and no loss of performance. Its impossible to detect the reducer, moulded as it is from the hose itself. I had no idea it was there.
I was able to smoothly carve it out with a craft knife. Glued air hose back with silicone as you showed in your photo.

I am not happy with all the hoses and connections that seem to be part of the 'emission breather system'. is it possible just to remove them and maybe keep a small breather hose to feed crankcase fumes into the air box?

[naughty lee]

Hi all, thanks to you all for the info and help. I ground down the variator boss, drilled three holes in muffler end and removed air box, changed to 6.5g rollers and fitted 1000rpm spring. 46mph anywhere very quickly with a few mph left if its a long straight. Acceleration is loads better too. I think i could still shave a bit more off the boss, i will check later and check the plug. Got a 90 jet in there for now but with no air box i might up it some more. Shortening the boss is like fitting a gear up kit. thanks again guys.

Mark the variator again right near the outer edge, if you skim too much off though, there are two pitfalls... The outer variator will start hitting your starter bendix, and/or your kickstart spigot will not reach its mating face ( both of these faults can be remedied by fitting a washer right behind all your variator assembly )

Just shave it off 1mm at a time
If you can get 53-57mph on the flat, that will be 60+ downhill

[phatboy]

Hi all, thanks to you all for the info and help. I ground down the variator boss, drilled three holes in muffler end and removed air box, changed to 6.5g rollers and fitted 1000rpm spring. 46mph anywhere very quickly with a few mph left if its a long straight. Acceleration is loads better too. I think i could still shave a bit more off the boss, i will check later and check the plug. Got a 90 jet in there for now but with no air box i might up it some more. Shortening the boss is like fitting a gear up kit. thanks again guys.

where did you drill holes in muffler exactly, and how big? did it make it a lot louder?

The restriction is placed where the white sealing is on the picture and will have to be cut or drilled out.

hey thanks for this, i like free mods, maybe its not well known, with all my searching i'm surprised i haven't seen it until now

i did not cut my hose in half, i carefully cut out the restriction with fine tip wood carving knives, then dremeled the rough edges, took a while but hose looks totally stock from the outside. just did it haven't rode it like this yet. wondering if i have to upjet now, have an 88 main jet on there (i have a 72cc bbk, stock head no other mods)