hillwilliam
ArboristSite Operative
Holy smokes! I've been pretty distracted and looking over my shoulder at the West Fork Complex Fire - 83,000 acres so far - but I am getting a little work done.
View attachment 302270
Now the carb stuff:
There isn't going to be anything new here; it's all bound to be in various places on AS. A couple of the tricks I learned here, and I don't know where the credit goes. It may help someone to find this stuff in one spot, though.
I can't call myself a saw builder, but I've done up quite a few carbs, mostly bigger ones, pretty much this way, going back about 25 yrs. I've never been scientific about it, other than timed test cuts. I haven't run a saw at low altitude for over 30 yrs., so I can't say. But these mods work well here (my house is at 8,000') and at well over 10,000' altitude.
This carb is off a 372 that I'm modding for someone else. The plan was to trim the limiting tabs to allow proper tuning. You may be able to see in the photo that both jets are as rich as they can go. Stock saw actually ran pretty nicely this way. The guy doesn't want 'nicely' - he wants 'gnarly'. Okey doke.
Is this picture fuzzy, or is it just my eyes?
View attachment 302272
I ended up cutting the limiters completely off, because they seemed to want to slip on the little splines.
Next is to grind some metal off the shafts. Plenty of meat is left where it needs to be, and I've never had a problem (yet) from lost strength.
I cut the ends of the screws off and I grind the heads down, leaving just enough to get a good bite with a screw driver. I'll use Loctite on final assembly.
View attachment 302274
Precise boring of the carb venturi would be good, but careful grinding works. You could just remove any casting flash, but I go farther. The last one I did was on a beater 372 with a big barrel top end. I took the venturi to 19mm on that one, and it idles kind of funky. (Not an air leak, but that old saw idled funky anyway.)
I'm going to 18.5mm on this one. (It ended up working fine on this nearly new saw.)
Grind, check, repeat, going for the best uniformity I can get. I know for sure that it's possible to go to 19mm on these little carbs without going into any passages. I also know that I have ground into a passage at 18.5mm. It sucks to buy an new carb or get out the JB Weld.
Then I polish up the venturi, give everything a good cleaning and reassemble. I set the metering lever flush with the top of one gasket. Then I add another gasket to enlarge the metering chamber a little.
View attachment 302276
Then I button everything up and tune to the idiosyncrasies of the saw.
It really doesn't take me long to do these mods, and I'm so slow that it takes me an hour and a half to watch 60 Minutes.
On my next saw, I need to try the carb mods and the muffler mods separately to attempt to document gains. I did both on this one before I tried it. To me, it made a huge gain in power/ speed in timed cuts with muff mods and carb mods. I even called the owner to check again if he still wanted it ported. Yup, I started porting the next day. Now it runs like it oughta.
Of course, you could just see about retrofitting a bigger carb. That works too.
I hope to get some positive critique on my redneck methods. It seems to work pretty well without getting differential pressures too out of balance. Still enough air velocity in the venturi to suck plenty of fuel in.
Hope this does somebody some good.
View attachment 302270
Now the carb stuff:
There isn't going to be anything new here; it's all bound to be in various places on AS. A couple of the tricks I learned here, and I don't know where the credit goes. It may help someone to find this stuff in one spot, though.
I can't call myself a saw builder, but I've done up quite a few carbs, mostly bigger ones, pretty much this way, going back about 25 yrs. I've never been scientific about it, other than timed test cuts. I haven't run a saw at low altitude for over 30 yrs., so I can't say. But these mods work well here (my house is at 8,000') and at well over 10,000' altitude.
This carb is off a 372 that I'm modding for someone else. The plan was to trim the limiting tabs to allow proper tuning. You may be able to see in the photo that both jets are as rich as they can go. Stock saw actually ran pretty nicely this way. The guy doesn't want 'nicely' - he wants 'gnarly'. Okey doke.
Is this picture fuzzy, or is it just my eyes?
View attachment 302272
I ended up cutting the limiters completely off, because they seemed to want to slip on the little splines.
Next is to grind some metal off the shafts. Plenty of meat is left where it needs to be, and I've never had a problem (yet) from lost strength.
I cut the ends of the screws off and I grind the heads down, leaving just enough to get a good bite with a screw driver. I'll use Loctite on final assembly.
View attachment 302274
Precise boring of the carb venturi would be good, but careful grinding works. You could just remove any casting flash, but I go farther. The last one I did was on a beater 372 with a big barrel top end. I took the venturi to 19mm on that one, and it idles kind of funky. (Not an air leak, but that old saw idled funky anyway.)
I'm going to 18.5mm on this one. (It ended up working fine on this nearly new saw.)
Grind, check, repeat, going for the best uniformity I can get. I know for sure that it's possible to go to 19mm on these little carbs without going into any passages. I also know that I have ground into a passage at 18.5mm. It sucks to buy an new carb or get out the JB Weld.
Then I polish up the venturi, give everything a good cleaning and reassemble. I set the metering lever flush with the top of one gasket. Then I add another gasket to enlarge the metering chamber a little.
View attachment 302276
Then I button everything up and tune to the idiosyncrasies of the saw.
It really doesn't take me long to do these mods, and I'm so slow that it takes me an hour and a half to watch 60 Minutes.
On my next saw, I need to try the carb mods and the muffler mods separately to attempt to document gains. I did both on this one before I tried it. To me, it made a huge gain in power/ speed in timed cuts with muff mods and carb mods. I even called the owner to check again if he still wanted it ported. Yup, I started porting the next day. Now it runs like it oughta.
Of course, you could just see about retrofitting a bigger carb. That works too.
I hope to get some positive critique on my redneck methods. It seems to work pretty well without getting differential pressures too out of balance. Still enough air velocity in the venturi to suck plenty of fuel in.
Hope this does somebody some good.