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...
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
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)
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