George Jones
Well-Known OPE Member
- Local time
- 2:32 PM
- User ID
- 3988
- Joined
- Sep 6, 2017
- Messages
- 8
- Reaction score
- 14
- Location
- Greenfield, Mass
Hi,
I am considering trying to mod some of my work saws and am trying to get an overall picture of how I can raise performance. I apologize if these are annoyingly common questions, but there are still some very basic concepts which I have not been able to fully grasp. I have been logging full time for almost a decade but am still embarrassingly ignorant on some fronts.
Carb:
-I understand opening up intake and exhaust to increase airflow, but I dont see how this can result in higher performance unless fuel is increased also. Are modifications made to the stock carb, or is it just a matter of adjusting the jets? If so, how does one increase RPM without leaning out the saw too much resulting in failure? Is increasing High jet rpm even that desirable? I want the chain to move faster under load, is this mostly controlled by the High or Low jet?
-Basically I have always run stock saws (mostly 372s, 390s, 395s, and 5262s) and really kept my hands off the jets. I have read the Madsens articles on tuning and have a tach, but the finer points of what Im really doing when I mess with those screws still eludes me, and Im afraid that if I do it wrong I will kill the saw.
Exhaust:
-I believe that the muffler needs to basically bounce some of the unburned oil left in the exhaust gasses back at the exhaust port to help lubricate the piston. For this reason most stock muffler ports are located on the side, rather than the front of the muffler. In the course of opening the muffler up to increase airflow, should all additional ports be likewise located on the sides? Is there a limit to how much additional openings should be made, say 2x or 3x the stock openings?
Piston and Flywheel:
-I have heard that reducing weight of the piston and flywheel can boost performance. Is this true? Is removing a small amount of metal from the underside of the piston advisable? If removing material from the flywheel, is there a risk of unbalancing it, resulting in higher vibrations? Is any of this a good idea?
Cylinder:
-I have read a lot about squish and base gaskets but still dont fully get it. By moving the cylinder down, the size of the combustion chamber is reduced, increasing compression. As a full time chopper the idea of removing the cylinder gasket to achieve this seems crazy, so the cylinder would need to be cut down on a lathe. I read "squish numbers" like .020" but have no idea how this would be measured.
-Lowering the cylinder seems like it would also alter timing, but Im not sure exactly how. I guess it would make the exhaust port open later, or farther from TDC, since it opens from the top, and the intake port open sooner, since it opens from the bottom? Transfers would also open later? So should these ports all be altered to account for that?
-The inside of the cylinder has a coating or plating of some sort which should not be compromised, correct? Do the insides of the ports also have this plating? Will changing the shape of ports on the cylinder wall cause the plating to wear off? What steps need to be taken to protect the plating/ how important is it?
Thanks for any help, I like thinking about this stuff and would like to tinker with my saws at some point, but since I rely on them to make my living, and theyre so damn expensive, I just want to have a fuller understand of what exactly is going on. I dont know anybody who mods saws that I can pester with stupid questions, all I have is you guys!
I am considering trying to mod some of my work saws and am trying to get an overall picture of how I can raise performance. I apologize if these are annoyingly common questions, but there are still some very basic concepts which I have not been able to fully grasp. I have been logging full time for almost a decade but am still embarrassingly ignorant on some fronts.
Carb:
-I understand opening up intake and exhaust to increase airflow, but I dont see how this can result in higher performance unless fuel is increased also. Are modifications made to the stock carb, or is it just a matter of adjusting the jets? If so, how does one increase RPM without leaning out the saw too much resulting in failure? Is increasing High jet rpm even that desirable? I want the chain to move faster under load, is this mostly controlled by the High or Low jet?
-Basically I have always run stock saws (mostly 372s, 390s, 395s, and 5262s) and really kept my hands off the jets. I have read the Madsens articles on tuning and have a tach, but the finer points of what Im really doing when I mess with those screws still eludes me, and Im afraid that if I do it wrong I will kill the saw.
Exhaust:
-I believe that the muffler needs to basically bounce some of the unburned oil left in the exhaust gasses back at the exhaust port to help lubricate the piston. For this reason most stock muffler ports are located on the side, rather than the front of the muffler. In the course of opening the muffler up to increase airflow, should all additional ports be likewise located on the sides? Is there a limit to how much additional openings should be made, say 2x or 3x the stock openings?
Piston and Flywheel:
-I have heard that reducing weight of the piston and flywheel can boost performance. Is this true? Is removing a small amount of metal from the underside of the piston advisable? If removing material from the flywheel, is there a risk of unbalancing it, resulting in higher vibrations? Is any of this a good idea?
Cylinder:
-I have read a lot about squish and base gaskets but still dont fully get it. By moving the cylinder down, the size of the combustion chamber is reduced, increasing compression. As a full time chopper the idea of removing the cylinder gasket to achieve this seems crazy, so the cylinder would need to be cut down on a lathe. I read "squish numbers" like .020" but have no idea how this would be measured.
-Lowering the cylinder seems like it would also alter timing, but Im not sure exactly how. I guess it would make the exhaust port open later, or farther from TDC, since it opens from the top, and the intake port open sooner, since it opens from the bottom? Transfers would also open later? So should these ports all be altered to account for that?
-The inside of the cylinder has a coating or plating of some sort which should not be compromised, correct? Do the insides of the ports also have this plating? Will changing the shape of ports on the cylinder wall cause the plating to wear off? What steps need to be taken to protect the plating/ how important is it?
Thanks for any help, I like thinking about this stuff and would like to tinker with my saws at some point, but since I rely on them to make my living, and theyre so damn expensive, I just want to have a fuller understand of what exactly is going on. I dont know anybody who mods saws that I can pester with stupid questions, all I have is you guys!
