Chainsaw Repair

Stock chainsaw carbs are pitifully small for the cc's of the motor compared to conventional 2-strokes. But due to small space constrictions,stud width etc,it's not often easy to just install a bigger carb and have everything fit and function as stock in a work saw. My answer starting in 1986 is to simply bore out the venturi of the stock carb to make a substantial gain in venturi area and airflow. The Tillotson HS,the Walbro WJ and the Tillotson HT can all be easily bored for a great boost in performance.
This involves stripping the carb down completely,then it's a quick simple job for a machinist to bore the venturi to specs,and smooth and polish the bore. Now I normally bored the carbs myself on a good drill press with a solid drill press vise,exercising care,using a slow drill speed and generous cutting oil. If you attempt to do it yourself you better practice on a junk carb first to see if you can do it and not damage the carb,otherwise your machinist buddy can do it better and polish the entire bore while it's still spinning in the lathe.
Boring the carb is just what chainsaws badly need and you will be rewarded with a great increase in power all thru the rpm range.
A bored HS for example will have about a 20% gain in venturi area and airflow,you will find that your highspeed screw may need to be out further turns than stock.
HS carb- Bore to 3/4"
WJ carb-Bore out to 49/64"
HT carb- 63/64"

Even a stock saw will respond well.
As a comparison,a 100cc motorcycle or Kart will use a 24mm to 30mm carb,the WJ carb on a similar size saw is about 17.5 mm,FAR smaller than ideal,laughable really...
I've done hundreds of these over the years and it was always included in any saw mod.

Same here Mike.
Summer of 1988 I went to Sayward, B.C. for the first time and ran my 064AV in the stock appearing 100cc and under event.
Ron Hartill was running a 100cc Poulan Pro655, I was running my 85cc 064 with .030 off the cylinder base, .040 off the intake skirt of the piston and 4 deep wide finger ports.

I was still running the stock WJ carb with no choke butterfly and shaft. I bored out the venturi, can't remember how much.
We had to run the shows supplied fuel, we were cutting 16" round lathe turned cottonwood ,  cut the day before and it was wet.
Cold start, 3 cuts down, up, down. Running in pairs on 2 logs.
When my turn came to warm up Husqvarna dealer Bob Walker ran over to me and tried to get me disqualified for running holes in my muffler. Lol.
 You couldn't even see the holes because I had the perforated fire guard front muffler cover.
Al Boyko and some of the other guys had a meeting with Bob and the decision was I could run.
Herlihy was running a 056Mag ll across from me in the other log, I was starting my 3rd cut and he was just starting his second.
First time I cut western cottonwood and it was spongy, I tried to push the saw through the last inch and I jammed up the chain.
With a rocking up and down on the bar/chain I freed it up and finished my cut. Lost a good second or two .....Ron came in 1st.
So later that fall back home I installed a 084 HT on the 064 and like you said it was a bugger to mate up, I even made my own linkage .
Had big plans to run it in Sayward the next summer of '89 but Stihl hired me as a technical services manager to work out of their Edmonton branch. Never made it back to Sayward.
Here's my 064 with HT carb and the chain I ran in the Sayward cottonwood of 1988.

I'll bet the carb was hard to mount,but it and the chain look very familiar.
I adapted the Mag2 piston and cylinder to get 99.8cc in 2 064 hotsaws,wasn't really hard once I figured it out,I relocated the sparkplug hole to keep stock appearance,because 056 plug hole is directly over piston.then some faller customers started demanding 100cc 064's,I explained they were just for racing and may not last a day of real work,and I refused any warranty on top end,but they insisted so I ended up building almost a dozen with the stock bored WJ. Amazingly they were all fine

Yes,a perfectly stock looking 064 hotsaw with a bored race HT hidden inside,it's also 100cc with a Mag2 piston and cyl. adapted.

Thanks for posting the photo.

I found that the 2094/2095 saws were incredibly easy to mount the HT on,
took about an hour and a simple bracket,the 084 boot fit perfectly so I built several good hotsaws from those.
But for modded worksaws carb boring is the best improvement for the cost and effort. I did try boring a few smaller carbs,but trying to bore the 372 carb I found was not worth the effort,it's just too puny to start with,better just to install the entire intake and carb from a 385/390.
I also used to perform some high speed circuit mods on the HS and WJ,but I don't have photos to detail such mods here. Also some WJ's suffered from a low speed circuit restriction which I easily cured and used to perform when installing a carb kit during a tune-up,this really helped them idle better and accelerate faster.