Count me in the hack club. Time isn’t money for me usually, and even when it is a faster saw isn’t what matters to me. Simply don’t like to go backwards in performance. It’s not behind by much according to my certified and bonified dyno hands lmao!
How far out on the H screw are you? After spending hours modifying and testing the zama on my 7900 and destroying several carbs in the learning process I can say... just buy the walbro if you want more power. It’s easier lol. My mods involved enlarging the venturi from 16.6mm to 17mm. As well as drilling the H main jet to .55 and thinning the shafts. I do not touch the low speed jetting, that part of the carb fed plenty of fuel for me. Definitely makes a difference, but time consuming. Be careful thinning the choke shaft as it only has a blade on one side. Easy to make it too weak and break the shaft. The walbro you start with a 17.5mm venturi and .64 jet stock. All I do on them is thin the shafts and they run good. However the zama is good carb on a stock or lightly modified saw. It works well for that application.
Great tips thanks for sharing. No I haven’t modded it yet, slapped it on box stock. Wanted to make sure the carb swap fixed all my problems before messing with it.
A stock C3M has a Venturi diameter of 17mm. I’m out at 2 turns on the High speed. Like I said above it’s not down by much and nowhere near made the saw a dog, still runs strong. My dyno hands could be full of *s-worde too, hard to tell. Gonna do some basics like thinning shafts and stuff. I need to go at this slow unlike when I tried modding the RWJ.
It’s 16.6mm at the smallest part. I open that to 17mm carefully at the top of the bore with a burr. You could also punch out the nozzle and bore it out on a drill press too. But that takes more time.
At 2 turns out you’ll run out of fuel like I did in the wintertime on my ported 7900. Start with drilling the H main jet to the next size up. You want to be around 1 - 1.5 turns out on the H at your ideal tune. Then thin the shafts. 
That part I circled is what you drill to get more fuel on the H screw. My L screw was sitting at an acceptable 1 - 1 1/4 turn out. I left that alone. It is very easy to mess up the carburetor drilling the low speed circuits and it isn’t needed like some say. I put hours of work into my 50$ C3m carb when I could have just slapped on a 70$ HD carb for 20$ more... I can’t say it was worth my time honestly. But you might as well experiment since you have the carb already. Start with drilling the main jet and thinning the shafts. That should be satisfactory. Boring it out isn’t totally necessary and takes time, but it is a gain.
At 84 cc I would go to a bigger carb but that’s just me.My problem with the stock 64xx type carb is it would run great with stock circuits on stock type saw but it will die in the woods feeding this thing @84cc. It was all done with a single port muffler mod during break in. The dual port will make it worse I'm sure. Carb settings went to 2L 2.2H it's done.
The transition is horrible anywhere on the trigger. Mods did little. Ten seconds in the cut and it's scary lean. I can get that back again but should I just move to bigger carb beyond 17.5mm or go back in and start with another carb a little bigger and not kill off the transition to the H circuit?
Been out of carb work for too long
You guys have time to play with these saws, I really don't right now but would like to get this thing much better, its sad and will cook.
Edit: I have another stock carb here. After two this is becoming a pia.
See that's just it. No one is running this set up over about 78cc. Still have the stock smurf stroke but it's hungry and getting hot.
Idk but ported it a bit and it just won't stay fat.
There's the HD30 from the 375K power cut. Bolts right in with zero changes.
part number 503 281 811
