Modded FA50 vm18 jetting

I understand that jetting advice is free and worth every penny you pay for it lol. But I would like to pick your brains as to what range of jetting is normal for a setup similar to mine.

The bike

89 fa50

Treatland big bore kit

Shaved head

Ported reed block

Boyesen 2 stage reeds

Vm18 carb

MLM intake

LeoVince pipe modded from some other moped

Stock timing

Deleted oil injection 50-1 premix e0 fuel

Right out of the box I lowered the float level. It was far too high as shipped for the angle my intake sits at and flooded immediately.

I know the idle jet is too big because I’ve got a lot of turns on the air screw and the choke is unusable. I’ve got an assortment coming.

The clip is second from bottom and the bike runs well enough. Perhaps a little soft on bottom but it’s very strong about 20mph and tops out at 30. It’s a little bubbly sounding at steady state cruise around 1/2 throttle. 3/4 to WOT doesn’t seem to net any extra acceleration or speed

Mainly want your opinion if this current tune is safe enough to get some miles on the moped and really dig into dialing the jetting in. (edited)


Re: Modded FA50 vm18 jetting

Any changes to the jets? IMO the stock 70 is usually too lean and the 30 idle is too rich for most bikes, but idk how your hack n weld one off FA is gonna run. I’d say if youre worried about seizing (and you should be w/ that kit) go rich all around (prolly like 95 main and keep the 30 idle) and work your way down. Better to foul a plug than seize right? HFFS on the wiki man

Re: Modded FA50 vm18 jetting

I like your rear disc conversion. I bet helps stop it a lot better. I wish I had better brakes on my QT’s.

Re: Modded FA50 vm18 jetting

Can you share the process how to convert to the rear brake disc ?

Re: Modded FA50 vm18 jetting

I am also working on a FA50 that my dad left me when he passed away this year. Big bore kit 65cc? - Circuit pipe, Boyesen 2 stage reeds, MLM VM18 intake, VM18.

90 Main

15 Idle

Starts and idles great, responds to choke lever on start. Gets to 20mph no problem then that's it. I had a 65 main in it first and it behaved about the same. I can get 25 mph down a hill. I did bend the reed stop out a little so I dont know if that messed up my performance. 90 main is the largest I have right now, think it needs more?

Re: Modded FA50 vm18 jetting

Jack Rutherford /

90 seems high. If you are over jetted, it will kill your top speed. I’d try an 85 main and see if it runs better.

Re: Modded FA50 vm18 jetting


Your plug looks okay enough to testdrive to me

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