Any tips on 272 or 372 stock appearing porting etc.

[rolloman]

Building either a 272 or 372 and need help

 

[timberwolf]

372 is a newer design, nicer to run as a work with more options for aftermarket parts which will make getting closer to 5cube class limit easier. You can run into the odd one with a limited coil, but thats easy to swap. 4 port design so easy to get transfer flow.

That said the 272s rev up high and can be done up well but sit low in most CC classes unless significant bore and plate work is done. 2 port transfer design so a bit more work to get top end transfer flow. 272 intake is also quite restrictive so rework is required in that area to make a real racer out of it.

 

[rolloman]

Is there any good sources for boring and cylinder plate.

 

[SpaayDawg]

These might get you started.

HiPo bolt on's

Porting vid 1

There are 13 vids I think.

 

[rolloman]

cool vidieos, thanks

 

[SawGarage]

These might get you started.

HiPo bolt on's

Porting vid 1

There are 13 vids I think.

well then...guess they don't need to be too clean, now do they!! those ports were NOT too consistent, or smoothed out for flow...

but i'm from the Northeast, what do i Know

 

[trappermike]

Pros and cons for both saws...
The 372 has a really nice cylinder to work with,and there is a modded domed piston with 4 transfer windows available for them,they increase power dramatically. Add some porting and they are a really strong saw. The short-coming-They are cursed with a small miserable carb,and adapting a different larger one that hooks up to everything(Throttle,fuel line,choke,impulse hose etc.) is difficult to find. I've found that boring the stock carb out and polishing the bore and modifying the fuel circuits is the best answer.
The 272 is a great saw,takes to standard mods well,just it has a bit of an odd shaped intake port which needs a little work,but not difficult. As far as the carb goes it has the good old HS Tillotson which has a larger bore than the 372 carb stock,and can be easily bored out larger,I have 2 different sizes I bore HS carbs out to,larger and extreme,both work well.
Both good saws to modify,each with it's pluses,one day I'll find a real carb to adapt to the 372 and get rid of the stocker for good.

 

[SawGarage]

Pros and cons for both saws...
The 372 has a really nice cylinder to work with,and there is a modded domed piston with 4 transfer windows available for them,they increase power dramatically. Add some porting and they are a really strong saw. The short-coming-They are cursed with a small miserable carb,and adapting a different larger one that hooks up to everything(Throttle,fuel line,choke,impulse hose etc.) is difficult to find. I've found that boring the stock carb out and polishing the bore and modifying the fuel circuits is the best answer.
The 272 is a great saw,takes to standard mods well,just it has a bit of an odd shaped intake port which needs a little work,but not difficult. As far as the carb goes it has the good old HS Tillotson which has a larger bore than the 372 carb stock,and can be easily bored out larger,I have 2 different sizes I bore HS carbs out to,larger and extreme,both work well.
Both good saws to modify,each with it's pluses,one day I'll find a real carb to adapt to the 372 and get rid of the stocker for good.

Hey Mike,

I'll send ya a PM as well...as I have a couple questions/thoughts on the 372 carb issue....

thanks,

J

 

[trappermike]

I've looked at trying to fit other carbs to the 372,such as a 394 carb(WJ Walbro) and the common HS Tillotson carbs,but there is just no "slip-in" fit that I know of,mounting another carb looks difficult,especially while trying to retain the stock throttle,choke,air filter etc.
I just haven't had enough time to adapt something that will work with all necessary functions.
So far the best answer I have is to modify the stock carb,bore out and polish the throat.

As for porting it's pretty much the same basic stuff on both saws.

The 372 receives a terrific boost in power when I adapt a different piston to it and also dome the piston for a compression increase. The piston I use feeds a much larger volume of fuel to the 372's transfer ports because it has the "windows" in both sides to feed the transfer ports. The stock 372 piston blocks off the transfer ports in the crankcase at BDC, just when the transfer ports in the cyl. are open.

Look at a 372 for yourself with the cyl. off,when the piston is at BDC it is blocking off the transfer port openings in the bottom of the cylinder.

 

[PARTSWOODCHUCK]

The 372 receives a terrific boost in power when I adapt a different piston to it and also dome the piston for a compression increase. The piston I use feeds a much larger volume of fuel to the 372's transfer ports because it has the "windows" in both sides to feed the transfer ports. The stock 372 piston blocks off the transfer ports in the crankcase at BDC, just when the transfer ports in the cyl. are open.

Look at a 372 for yourself with the cyl. off,when the piston is at BDC it is blocking off the transfer port openings in the bottom of the cylinder.[/QUOTE]


Any way we can squeeze out wich piston you use? I'm building a 372 for the county fairs, and I have a hot 371 to beat this year. You can PM if you would like I won't tell nobody

 

[mark09]

Pros and cons for both saws...
The 372 has a really nice cylinder to work with,and there is a modded domed piston with 4 transfer windows available for them,they increase power dramatically. Add some porting and they are a really strong saw. The short-coming-They are cursed with a small miserable carb,and adapting a different larger one that hooks up to everything(Throttle,fuel line,choke,impulse hose etc.) is difficult to find. I've found that boring the stock carb out and polishing the bore and modifying the fuel circuits is the best answer.
The 272 is a great saw,takes to standard mods well,just it has a bit of an odd shaped intake port which needs a little work,but not difficult. As far as the carb goes it has the good old HS Tillotson which has a larger bore than the 372 carb stock,and can be easily bored out larger,I have 2 different sizes I bore HS carbs out to,larger and extreme,both work well.
Both good saws to modify,each with it's pluses,one day I'll find a real carb to adapt to the 372 and get rid of the stocker for good.

if you add a second gasket to the metering side and bend the metering lever up to the diafram u get more reserve in the carb. the saw wont starve for gas at WOT. Be careful not to let the cover hit the metering lever or the saw will just flood with gas!!!

 

[mark09]

The 372 receives a terrific boost in power when I adapt a different piston to it and also dome the piston for a compression increase. The piston I use feeds a much larger volume of fuel to the 372's transfer ports because it has the "windows" in both sides to feed the transfer ports. The stock 372 piston blocks off the transfer ports in the crankcase at BDC, just when the transfer ports in the cyl. are open.

Look at a 372 for yourself with the cyl. off,when the piston is at BDC it is blocking off the transfer port openings in the bottom of the cylinder.

Any way we can squeeze out wich piston you use? I'm building a 372 for the county fairs, and I have a hot 371 to beat this year. You can PM if you would like I won't tell nobody[/QUOTE]

Yup its fast!!!! U need more than a piston mister half cookie!!!! lol!!!!:hmm3grin2orange::msp_flapper:

 

[trappermike]

Yes you can "squeeze" the trick piston with the modified dome from me,I sell them in 2 versions,one for stock or normally modified saws and one for competition saws.
These are not cheap aftermarket pistons,and the dome is machined and polished ready to go. Also for a few bucks more I include a lightweight wrist pin.
I was the person who originally developed this piston swap and mod back around 1998.
You can message me if you are interested. You need to buy a piston and machine it to do the mod. anyway,so you can purchase it from me ready to go,correctly measured and machined for your application.

 

[trappermike]

The stock carb on most professional saws is actually much smaller than is ideal even for a stock saw,and is really one of the biggest factors restricting the power output of the saw. Either enlarging the bore of the stock carb(If possible on that particular model),or adapting a larger carb will have a good affect on power output and not affect low speed power because the stock carb is just too small. I've been able to bore the 372 carbs out,it's not that easy to do with them,but of course helps power.On most types of saws carb boring is quick easy way to gain power.
I'm working on a carb swap for 372's to a larger carb and still retain all the saw's stock functions,which is necessary for most home and professional saws.The design of the 372 does not make carb swapping as easy as on the older Husky's.
For competition it's no so much of a problem to swap a bigger carb,when you don't need to worry about hooking up the choke,air filter etc.
In the past though,I've found boring out the stock carb to be an excellent mod. for any saw,motorcycles too,everything stock fits with no headaches!
I'm also not thrilled with the big names like Husky and Stihl going to Chinese made carbs as an obvious cost factor. I can't think of a person who would willingly hunt down and swap a Zama (For instance) carb onto his saw to boost performance.... Although they seem to run ok as intended on a stock saw.
I'm amazed that so many people overlook boring their carb when modifying their saws.

On smaller saws the Walbro WA,WT,and WAT model carbs are popular on them,and come in many bore sizes from very tiny to the largest. Often all you need to do is find another similar model Walbro off another machine with a larger bore,swap the throttle and choke shafts and whatever else,and you can swap on a much larger carb. I used to collect and save used Walbro's of those models(Which had large bores) for swaps.Basically put on a much bigger bore carb for free,if you are lucky to have scavenged a carb. For instance I like to use a Walbo from a small saw to replace one on a trimmer.

 

[husq2100]

Mike,

any thoughts on a good piston for a race 272? will be normal cylinder/head...cant run a 2 piece head in this class. Any advantage in using a 288 or 2100 carb...or just work the 272 carb?

cheers,
Serg

 

[husq2100]

also Mike, do you play with the POP or pop off pressure on the carbs?

 

[mark09]

can u tell us how you go about boring the carb? tools, size of boring, maybe some pic.

 

[trappermike]

Husq2100- Use an original piston for a race 272,preferably a new genuine one,jobber pistons won't cut it for extreme use. The piston can be modified several ways,mods like doming,but the piston must be measured and calculated correctly,to get max. gain and avoid engine damage.
I've experimented with altering the pop-off pressure on carbs,generally most popular mid and large size saws the factory pop-off setting is ok and needs no altering.I have only found on smaller saws where the vacuum strength is small that pop-off pressure had to be reduced with a lighter spring,to cure a lean running condition.

 

[trappermike]

Mark09- Carb boring can be applied to several models of popular carbs,some are easy and straight-forward,some can be tricky as not to ruin the carb.
The Tillotson HS is a good example,used on most older Huskys and Stihls. First the main carb block must be stripped down completely,shafts removed,needles,welch plugs,etc. Then you can take it to your machinist and ask him to bore the venturi (The smallest inner diameter of the carb bore,the most restricted part) to 3/4".The finish should be very smooth.
Determining how large a carb can be bored can only be found by trial and error,at some point you will machine into a critical passage and then the carb is junk.I've experimented on quite a few model carbs and sacrificed a few to find out how much they can be safely bored. Some carbs can't be over bored,it's just the way they're made...

 

[trappermike]

There actually 2 versions of the Tillotson HS carb,one with a small bore,and the more common one with the larger bore.Many older saws used the smaller bore HS,on these saws it's easy to swap in the larger bore HS carb body from another saw. A Homelite XL-12 for instance has the smaller bore carb,so swapping to the larger body is going to give a power gain,a bigger carb,bolt-on fit!
I'm not sure now,but I think 041 Stihls used the smaller Tillotson,so they could benefit too.