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#Post#: 84020--------------------------------------------------
Boring out carbs,more flow for more go
By: trappermike Date: January 4, 2019, 12:59 pm
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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.
#Post#: 84022--------------------------------------------------
Re: Boring out carbs,more flow for more go
By: trappermike Date: January 4, 2019, 6:34 pm
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I did once manage to fit a bored out race HT on a 100cc 064 and
keep it 100% stock appearing to comply with rules,but it was a
long tough labor of love I would never want to repeat,I had to
chop the carb mounting pad and studs out of the 064 airbox,and
chop the same out of an 084 airbox and graft it back into the
064 box. I got really lucky,the carb and linkage just barely fit
in and worked fine.
Again this is why boring the stock carb makes a lot of sense.
Ah once again I can't post the photo,I'm certainly no genius
with computers...
#Post#: 84026--------------------------------------------------
Re: Boring out carbs,more flow for more go
By: HolmenTree Date: January 4, 2019, 9:11 pm
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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.
#Post#: 84027--------------------------------------------------
Re: Boring out carbs,more flow for more go
By: HolmenTree Date: January 4, 2019, 9:27 pm
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It was my first time running in pairs too which screwed me up
seeing the other guy cutting in the corner of my eye throwing my
concentration off.
Up until then every contest I entered we cut solo one at a time.
#Post#: 84034--------------------------------------------------
Re: Boring out carbs,more flow for more go
By: trappermike Date: January 5, 2019, 8:16 am
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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
#Post#: 84036--------------------------------------------------
Re: Boring out carbs,more flow for more go
By: Chainsawrepair Date: January 5, 2019, 8:35 am
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[member=2926]trappermike[/member]
Is this where you was wanting it?
Can you see it. I just copied others location in pipes for ya.
[img]
HTML http://chainsawrepair.createaforum.com/index.php?action=dlattach;topic=3720.0;attach=26144;image[/img]
#Post#: 84039--------------------------------------------------
Re: Boring out carbs,more flow for more go
By: trappermike Date: January 5, 2019, 8:55 am
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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.
#Post#: 84040--------------------------------------------------
Re: Boring out carbs,more flow for more go
By: HolmenTree Date: January 5, 2019, 11:00 am
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I ran my pipe on my 064 at 45° angle. In this picture from
around 1993 it shows me at the end of the log running my
bikesaw. A local logger in the fore ground is running my pipe
and roller nose bar I sold him on his 064.
#Post#: 84041--------------------------------------------------
Re: Boring out carbs,more flow for more go
By: trappermike Date: January 5, 2019, 11:32 am
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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.
#Post#: 84072--------------------------------------------------
Re: Boring out carbs,more flow for more go
By: Chainsawrepair Date: January 7, 2019, 2:36 pm
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Guy that lives not far from me. He is here too.
HTML https://youtu.be/P3lQTUCfXbQ
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