36" bar

[Ashful]

Almost forgot... checked max RPM with this big bar mounted, and found it was only 10,600 on a cold engine at WOT. Was getting just a bit of 4-stroking at top, so seemed all was tuned well, but surprised to see RPM's so low. I think it's spec'd at 13,000. Never checked it on the 28" bar (which looks tiny / wimpy, after mounting the 36"!).

 

[DexterDay]

Did you tune it on the 28"?

 

[Ashful]

Yes... and I did consider re-tuning for 36", but here's why I didn't:

1. When setting "L", clutch is not even engaged, bar length has no effect.
2. When setting "H", you play the game between max RPM and four-stroking... but that's only a means to an end. The real goal is to have the saw adjusted so that proper mix is achieved under load, and bar length ain't really the primary factor on load, when I can flat out stall the saw with any size bar.

I am guessing though, that the 36" bar is why I'm only hitting 10,600. I don't believe this is a tuning issue, but simply what this saw can spin with that kind of load. I will try to check that this weekend.

 

[MasterMech]

When setting "H", you play the game between max RPM and four-stroking... but that's only a means to an end. The real goal is to have the saw adjusted so that proper mix is achieved under load, and bar length ain't really the primary factor on load, when I can flat out stall the saw with any size bar.

Stihl (and Husky too) uses the H setting to limit max RPM on saws with unlimited ignition coils. In recent years, saws are switching to running leaner fuel systems and utilizing electronics in the coil to set a "redline" RPM. So theoretically, the newer saws are set to the optimum fuel/air ratio regardless of what size bar is on it. Do you think an M-Tronic or Auto-Tune saw knows what size bar is on it? Many things affect the optimum fuel settings on your carburetor. Barometric pressure (altitude/weather), ambient temperature, fuel type/quality, amongst other things. Bar length is not one of them. I see no reason you can't lean it out some to get closer to your saw's Max unloaded RPM spec (in your owners manual I believe).

 

[Ashful]

Okay... I'll do it!

That begs the question, though... why not just leave it lean when I switch back to 28"? It's not like I sit there pulling the throttle wide open under no load.

 

[DexterDay]

I dont know what the SOP is. But I always "Tune" w/ a bar on. It isnt much load. But compared to No Bar, it is a load indeed. And as MM says, the saw is designed to rum at a certain RPM (depends on Saw), so why not run as close to it as possible. Obviously veering towards the side of safety (rich). But running a saw at 10,000 R's, that can and will run 12,000 is a waste. IMO.

Run that MoFo! LOL

 

[Ashful]

There's also the factor of how much I trust this tach in non-contact mode!

 

[smokinj]

If you got a big round tune it in the cut!

 

[Ashful]

Might take two people to do that safely. Will have to see if I can find video on that procedure. As it is, tuning this extremely nose-heavy rig is a challenge on the ground! Might try clamping rear handle down to my bench, instead.

 

[smokinj]

If you can tune by ear you just drop to idle make small adjustment repeat untill happy