Checking your tune in the wood

[thook]

I don't know that my Makita 520i has a rev limiter. It is an older'ish saw. However, would this method apply to tuning it? I take it the "4 stroking" refers to the "rough" sound of the engine until its starts "clearing out"?

Edit: Nevermind....got it!

 

[russhd1997]

Repped ya Brad, Parisw and Andy. Excellent videos and advise.

 

[046]

excellent videos!!

 

[mountainlake]

Unless you're in really small soft wood a 7900 should sit on around 11-12k rpm in the cut (maybe less) so shouldn't get near the limiter. Even modded 7900's like I own will only sit on around 12k rpm in reasonable wood.

I'd think a stock 7900 should be run between 9000 to 9500 RPM where the peak HP is, HP drops off fast at higher RPM's, Maybe Troll will check where the peak HP RPM is on the 7900. Steve

 

[Stihlman441]

This is a vid of a 880 with rev limit coil but you can hear the 4 stroking when the weight is taken off.
Allso note how the chain is lifted out of the bar groove as it enters the thick bark of the Stringbark log,this is an example why us Ozzys tend to use the next size up saw than other people around the world for the size wood.Stringbark is a pain in the you know what,when the chain is lifted out of the bar groove bark fibres get under and clog things up,this allso happens when ya brake through as well,there is puddles of thick gooy sap in spots as well.

[video=youtube;RIlsjOn1gFE]http://www.youtube.com/watch?v=RIlsjOn1gFE[/video]

 

[MCW]

I'd think a stock 7900 should be run between 9000 to 9500 RPM where the peak HP is, HP drops off fast at higher RPM's, Maybe Troll will check where the peak HP RPM is on the 7900. Steve

It depends on the saw's porting and the port timing Steve. Certain saw models perform better at different revs. It also depends on how much people load the saw up during the cut or even chain setup and sprocket size.
The point I was trying to make though was that hitting the 13,500rpm limiter in the cut on a stock 7900 is highly unlikely.

 

[mountainlake]

It depends on the saw's porting and the port timing Steve. Certain saw models perform better at different revs. It also depends on how much people load the saw up during the cut or even chain setup and sprocket size.
The point I was trying to make though was that hitting the 13,500rpm limiter in the cut on a stock 7900 is highly unlikely.

I'll bet if Saw Troll comes up with the max HP number on a stock 7900 it will be around 9000 to 9500 and that's where they should be run to cut the fastest. Certainly and modded run will make peak HP at higher RPM's. Steve

 

[MCW]

I'll bet if Saw Troll comes up with the max HP number on a stock 7900 it will be around 9000 to 9500 and that's where they should be run to cut the fastest. Certainly and modded run will make peak HP at higher RPM's. Steve

You may be right mate but the 7900's certainly don't cut the fastest at rpm's that low - they can certainly pull at that though and do have good torque. Stock saws do seem to like hanging around that 10,500-11,000rpm but it does depend on bar length, chain setup etc of course. About the only saw I own that can probably pull down that low in the cut and do it well is my 3120 - you can sit on that thing and it doesn't stop. Peak HP rpm means nothing if the saw can pull a faster chain speed in the cut. Chain speed in the cut is where the speed comes from.
I have checked a number of saws in the cut regarding rpms, both stock and modded.

 

[NORMZILLA44]

Just set my saw's with help at my saw shop. I wanted to put a tach on my 044. How many of you guy's put tach's on them, and run them at the max no load. For example 372-044 13,500 do you guy's run them there, or a couple hundred rpm's under? I know for max spped you need a tach. Norm.........

 

[Eccentric]

Just set my saw's with help at my saw shop. I wanted to put a tach on my 044. How many of you guy's put tach's on them, and run them at the max no load. For example 372-044 13,500 do you guy's run them there, or a couple hundred rpm's under? I know for max spped you need a tach. Norm.........

I don't use a tach at all. I set saws so they run like those two in the videos. Of course I mostly work on stuff that turns less than 12K!

 

[MCW]

Just set my saw's with help at my saw shop. I wanted to put a tach on my 044. How many of you guy's put tach's on them, and run them at the max no load. For example 372-044 13,500 do you guy's run them there, or a couple hundred rpm's under? I know for max spped you need a tach. Norm.........

Hey Norm. I've found that with longer bars in larger wood you seem to gain more performance by running them a little richer. For example Stihlman441's 660 that I fitted the BB kit to last weekend was pulling 12,500rpm with the stock cylinder and pulled like a train. Many here would probably tune their 660's to maybe 13,000-13,500rpm?
When Brad sent me out the two modded 390XP/XPG's they were tuned to 14,000rpm and cut like crazy. However I found they cut even "crazier" with longer bars (32") when tuned to around 13,600rpm. I normally use a tach to start with then tune in the wood and then recheck with the tach - just to make sure I haven't got something wrong along the way. I've found the odd saw, especially muffler modded, can be difficult to hear 4 stroking in the cut sometimes.

 

[Stihlman441]

Well said there Matt,i have been picked up before for running saws rich,if ya wont torque out of a 660,880 thats where ya get it from.I have never lean siezed a saw yet and whats the worst thing that can happen a bit of carbin,but with these synthetic oils its not a problem.
That stock 660 ya pulled apart has allways ran at 40:1 synthetic oil and around 12800 rpm wide open and how bad was the carbon i rest my case.Ya here about these ported saws running high rpm but realy what do ya gain ?.
Even brads 660 i have i found about 13800 is its sweet spot,but ya can lean it out to 14100 and it screems but how long will it last like that.
Anyway what would i know i just cut hardwood firewood.

Andrew

 

[mountainlake]

You may be right mate but the 7900's certainly don't cut the fastest at rpm's that low - they can certainly pull at that though and do have good torque. Stock saws do seem to like hanging around that 10,500-11,000rpm but it does depend on bar length, chain setup etc of course. About the only saw I own that can probably pull down that low in the cut and do it well is my 3120 - you can sit on that thing and it doesn't stop. Peak HP rpm means nothing if the saw can pull a faster chain speed in the cut. Chain speed in the cut is where the speed comes from.
I have checked a number of saws in the cut regarding rpms, both stock and modded.

Max HP and torque are what cuts and they both fall off fast over 9500 RPM. Found out the stock 7900 HP is at 7900 Rpm(oops meant 9500 RPM), any higher than that in the cut your cutting slower, the only way the keep the RPM up is by less pressure taking smaller chips. Watch some vids of Bsnelling, he runs at high RPM , meduim RPM and lugging it too much. The meduim RPM cuts the fastest every time. Steve

 

[MCW]

Max HP and torque are what cuts and they both fall off fast over 9500 RPM. Found out the stock 7900 max HP is at 7900 Rpm, any higher than that in the cut your cutting slower, the only way the keep the RPM up is by less pressure taking smaller chips. Watch some vids of Bsnelling, he runs at high RPM , meduim RPM and lugging it too much. The meduim RPM cuts the fastest every time. Steve

It may depend on the type of wood you cut as well. I certainly haven't found running rpm's that low with the felling work I've done in our hardwoods beneficial or efficient. I agree with the medium rpm's part cutting the fastest, I just don't agree that 7,900rpm with a 7900 is medium rpms - I would class that as the low end of the operating rpm scale. HP and torque curves are interesting but don't always work in the field the same as they do in theory. I would be interested to hear from other guys though about what rpm their fastest cutting is achieved at. I have loaded saws up to around 9,000rpm in the cut but they definately slow down too much. 10,000+ rpm has always shown to be the fastest when I've checked. Whether semi chisel in hardwood makes a difference I'm not sure. I cut very little softwood and have never checked rpms in that type of timber.

 

[blsnelling]

Most of my ported saws cut fastest in probably the 10,500 to 11,500 range. Much lower and you're just bogging the saw. Medium pressure is most always fastest. Obviously, we can't really compare stock vs ported optimum RPMs, since the ported saw will turn a higher RPM with similiar pressure.

 

[NORMZILLA44]

Some of the guy's I grew up cutting with, alway's cranke'd there saw way up, and lean. They may have limbed a little faster, and even been quicker in small stuff, but I walked away at the stump. Tried to explain to them about torque curve, and to hihg rpm's they were actually dropping torque. Like my hot rod day's they tach, and tach, but so high, and valve's float and you go backward's. Thank's Aaron, and thank you Matt real good info! Until recently I had never heard of tuning in wood. Seen quite a few lean seize's in my time friend's who cut with me, and went just a little to far. John parmeter's dad Will alway's tuned mine when I was a kid. Ear tune'd, and they alway's 4 cycled. Showe'd me how to do it, but we never did it in the wood. I think all the method's mentione'd are good, but do think of investing in a tach sometime's. Once my saw's are tune'd they stay that way, because I leave them alone. Norm.............................

 

[mountainlake]

It may depend on the type of wood you cut as well. I certainly haven't found running rpm's that low with the felling work I've done in our hardwoods beneficial or efficient. I agree with the medium rpm's part cutting the fastest, I just don't agree that 7,900rpm with a 7900 is medium rpms - I would class that as the low end of the operating rpm scale. HP and torque curves are interesting but don't always work in the field the same as they do in theory. I would be interested to hear from other guys though about what rpm their fastest cutting is achieved at. I have loaded saws up to around 9,000rpm in the cut but they definately slow down too much. 10,000+ rpm has always shown to be the fastest when I've checked. Whether semi chisel in hardwood makes a difference I'm not sure. I cut very little softwood and have never checked rpms in that type of timber.

I made a typo in the above post, meant 9500 RPM stock, in post NO 8 you had them running at 11000 to 12000 RPM which is way to high and missleading . Even 10000 is too high, if you look at HP graphs both HP and torque fall off fast above the rated HP, if they didn't don't you think they would rate them higher. Also torque increases up to a point at lower RPM's so you'ld be better off to run the 7900 at 9000 RPM rather than at 10000 RPM where you lose both HP and torque but it should be run at 9500 RPM where peak HP is. Steve

 

[blsnelling]

Are you talking stock or ported? If stock, I have no real experience. Most of my ported saws will cut fastest probably somewhere between 10,000 and 11,500.

 

[mountainlake]

Are you talking stock or ported? If stock, I have no real experience. Most of my ported saws will cut fastest probably somewhere between 10,000 and 11,500.

Stock, it makes sence that ported saw will make peak HP at higher RPM. Steve

 

[J.W Younger]

Faster the chain speed faster the cut. Tuning under load for highest chain speed with occasoinal 4 stroke when loading less will be the best mixture.
Tune for best power then tach for reference.