Fa50 powerjet mod for stock mikuni carb (D.I.Y.)

josh faykosh /

Hello all

Today I will be sharing with you all how I made and added a power jet to the stock little mikuni carb on my 83 Suzuki fa50. I spent about $20 usd on parts

First I must say I dont condone nor really recommend drilling or modifying a carburetor, they are fuel metering devices and can easily be damaged as well as damage your engine if you don't have things set right. I am not responsible for any damage or other problems to your carb, engine, or anything else if you decide to do this. I have spare parts so if I mess one up I dont care. Also I did not do this to the carb that is on the running bike. I also have not bolted this up yet for any form of performance testing. It is December and where I'm at there is snow on the ground. So that must wait for warmer days.

With that being said let's dive right in...

Parts list

3/8 square key stock

1 Grease injector needle (the kind that looks like a doctor's needle)

1 grease fitting m6x1.0

1 grease fitting m8x1.0

And an idle mix screw from another carb, mine came from an old quadrajet core from a chevy truck

Tools list

Set of small picks

Electric drill/assorted drill bits


Dremel with small file bits and cutoff wheel

Couple pairs of pliers (vice grips help too)

Taps m6x1.0, m8x1.0, and 10-32nf (machine thread)and their corresponding drill bits

17/64 drill bit

Locktite (I used red cause it's what I had)



Propane torch


This does involve heating of the fuel bowl with direct open flame make sure you COMPLETELY DRAIN, CLEAN, AND DRY the fuel bowl.

Remove the drain plug screw, I have flux paste so I used a paperclip to put the flux into the bottom of the hole then cut a piece of solder about 1/4 inch and drop it down the drain plug screw was. Hold the fuel bowl with a pair of pliers or a vice at about a 45 degree angle so that the fuel drain passage is in a "V" then use the torch to heat the fuel bowl and melt the solder. The goal is to block off the corner and disconnect the drain screw area from the overflow and doing it this way just works best on this particular carb. While you let it cool completely then take your handy little pick set and remove the springs and balls from the grease fittings and take some pliers and remove the little grease fitting from the end of the grease needle. After the fuel bowl has cooled take your m8x1.00 tap and tap threads about 5/16 deep into the place you removed the drain screw from. Then thread in your de-balled m8 grease fitting and your done with the fuel bowl, I also used my dremel with a small grinding ball and cleaned up the small hole on the inside of the fuel bowl. Also be sure to check for leaks before final assembly.

Now take your 3/8 keystock and cut a piece about 5/8 long and drill a hole centered on one of the sides about 5/16 deep most of the way but not all the way through. Dip the base of the needle into the flux and insert the base of the needle into the 17/64 hole and heat with your torch and solder the two pieces together make sure the needle points up as to not plug the needle with solder. Now because my fuel mix screw is 10/32 thread I take a #23 drill bit and drill all the way length wise through the end. and on one side I take the drill bit for the m6x1.00 tap and drill about halfway down the keystock and just through both sides of the base of the needle that was soldered in place and tap your threads for both the grease fitting and your adjustment screw and install both and if all works right you should be able to controle flow with the screw, you can test this by blowing through it and turning the screw, now the power jet is done.

Now take the carb main body and your new power jet and hold it across the intake side of the carb with the needle pointing down do this to find out how long the needle needs to be cut to it shouldn't be any longer than half throttle on your carb it can be shorter though, this sets at what point in the throttle the new jet will draw fuel and deliver it to the engine. Carefully sand or file the top of the carb to remove the casting line and make it smooth. And drill a small hole and use a dremel with a cone bit to gradually widen the hole till the new jet just fits and apply loctite around the new jet to secure it to the main body and let it dry make sure the grease fittings on the power jet and the fuel bowl are pointing the same direction now assemble your carb and take the fuel line and connect the 2 grease fittings and your done

I hope this was helpful I will update with some pictures of making the power jet when I make my next version, it was just a proof of concept and didn't think to take pics

Till next time



Re: Fa50 powerjet mod for stock mikuni carb (D.I.Y.)

What do you hope to achieve with this?

Re: Fa50 powerjet mod for stock mikuni carb (D.I.Y.)

josh faykosh /

A little bit more top speed and it's just fun to tinker and make things

Re: Fa50 powerjet mod for stock mikuni carb (D.I.Y.)

> josh faykosh Wrote:

> -------------------------------------------------------

> A little bit more top speed and it's just fun to tinker and make things

Hell yeah, why not

I like this

Re: Fa50 powerjet mod for stock mikuni carb (D.I.Y.)

josh faykosh /

My overall goal is 35mph on a consistent basis with fairly simple diy mods

Re: Fa50 powerjet mod for stock mikuni carb (D.I.Y.)

> josh faykosh Wrote:

> -------------------------------------------------------

> My overall goal is 35mph on a consistent basis with fairly simple diy

> mods

Just make sure you're going down hill with a tail wind , whenever you ride . LOL

Seriously , I like this little mod . ;)

If you're still running stock , you might consider relieving the piston crown at the ports and taking just a bit off the head mating surface .

Re: Fa50 powerjet mod for stock mikuni carb (D.I.Y.)

I'm Just from the school of "port first" and get big gains.

It's insane how much power can be gained with proper squish and moderate porting.

I will say tho that I like the idea of these on the fly jetting adjustments. Whatever it takes to get optimal mix. I do the same thing with precise metering/adjustment of the air entering the carb, I'm always tuned a lil lean, then adjust airbox flow until jetting is spot on.

It's been very wet here and my bikes were all pig rich, so I pulled one of the airbox tubes completely out and whammo! Big power is back!


Re: Fa50 powerjet mod for stock mikuni carb (D.I.Y.)

josh faykosh /

I have done a few things to my little bike. Added a couple crank gaskets to change my port timing I removed the little aluminum head gasket and lapped both mating surfaces to make sure they seal. A lot of things I do, I don't recommend but they work for me on my bike, and I do have a lot of fun moding, tinkering, and sharing the things I try

Re: Fa50 powerjet mod for stock mikuni carb (D.I.Y.)

josh faykosh /

My air cleaner setup is completely 0 restriction full flow so I don't have much issue there. I also have the fiberglass reeds on mine. Acceleration is great with the little thing just needs some top speed, most of why I did this mod in particular is I noticed once I got up to its max speed of 25mph. The last half to wide open throttle does nothing, the power jet only draws fuel when the throttle is from half to w.o.t.

Re: Fa50 powerjet mod for stock mikuni carb (D.I.Y.)

Sum ting wong ...

Top stock speed for an FA50 is 29 - 30 mph .

Mine does it all day and at times , when conditions are right , it'll see 33 for long periods on flat roads and no wind . That's with a worn out piston and ring with fairly low compression . I relieved the piston crown to help compensate . Other than that , all stock .

Re: Fa50 powerjet mod for stock mikuni carb (D.I.Y.)

josh faykosh /

Mine is around 27 average but no road where I am at is level and the wind don't stop blowing here in livingston. On a good day it will hit and hold around 30-33 that's why I said hit 35 consistently

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