stihl 440 porting beginner

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It`s kind of a package so I found but if you think of the basics of getting more air through the carb, that picks up more fuel from the venturi and how that mix gets to the crankcase, then up through the transfers to the top end, above the piston on the compression stroke is step one for me. Next its compression and spark creates the explosion that drives the piston down til the exhaust port opens and the exhaust port gases are spent, the upper transfers open and allow fresh mix to be pushed into the cylinder helping to push the last of the spent charge, exhaust , out the port. Many small steps are there that can be improved, some judicious port shaping, grinding required , and many small changes to the support system can be made.
Back to step one, intake of air, run a less restrictive air filter, bore the carb if possible, remove the choke assembly and install a primer setup all allows more air through the carb, feather the throttle shaft and plate. Grinding and shaping the intake port, grinding and shaping the upper transfers and the transfer tunnels themselves, directing the incoming charge back toward the intake side of the cylinder helps scavenge the spent exhaust gases and helps keep more of the incoming charge in the cylinder, not escaping through the still open exhaust port. Next it helps to tighten down the squish gap between the piston and cylinder head, remove the base gasket and seal the cylinder base to the crankcase raises compression , seal it with a suitable sealer. Always open to conjecture as to what sealant is best, never had a problem ever with any I have used. Next step is to open the exhaust some and reshape the exhaust port, how much depends on the width of the piston skirt or a percentage of the cylinder bore. Once the exhaust port is opened then the muffler exhaust flange needs to be opened just a hair larger than the port so no restriction is blocking the exhaust path, the muffler internals need to be accessed, remove restrictions inside the muffler, create a larger exhaust port in the muffler to the outside or create a second port, size depending on the extent of port work that has been done. I am not personally a believer of the 80% theory, often go more open but its a personal thing, go as big or small as you like. Next a small advance in the timing works well on most chainsaws, not all but its worth a shot, taking .020 off the woodruff on the crank key allows the flywheel to advance timing a few degrees, usually a safe bet but in some instances the engine will kick back excessively when trying to start it or another problem arises where the engine will not slow down as quickly as it should causing over run when the throttle trigger is released. . One will know when either of these symptoms occur and the flywheel adjusted. put back to original location is easy enough.
Other things like carb tuning, making sure fuel delivery is not restricted, good fuel lines, tank filter in new shape , small stuff all adds up to a good running saw. Things can be taken further but requires more work and more parts replaced or modified. Take this as an overview and not an actual blueprint, the study and improvements are an ever evolving thing/study and the basics is just a start into the craziness of engine porting that can ensue.
This is all great information. Thank you very much for your insight!
 
I did one not that long ago. Ports can be widened a fair amount. Watch out for ring ends. If you want any machine work done send it to me. I don't mind doing it for a few bucks.
 

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