Have I been tuning saws wrong

[Amp4027]

Just remove the throttle plate - it only restricts air flow anyway!

Have to - it gets in the way of the V-TEC turbo

I think treemonkey figured it up one time and it was like 7:1 or something like that

Thanks for the reply. Geez, 7:1, thats it? Almost sounds like it can run 87oct.... So 89oct gas like the ms200t manual says should be just fine then right?

 

[jmssaws]

Have to - it gets in the way of the V-TEC turbo

Thanks for the reply. Geez, 7:1, thats it? Almost sounds like it can run 87oct.... So 89oct gas like the ms200t manual says should be just fine then right?

Ive only seen a couple saws that were detonating. The 661 above is one but it wasn't from compression,it's only 170lb
I had just a little bit to much advance and a very tight squish.
I think stihl recommends 89 because it's usually better quality but it can also be older,the stations here sell little premium.

 

[mopar969]

Hmm okay so I know my question has been answered. but in regards to last comment I do run 93 octane gas. On some of my saws I tried 87 and the tune was way off compared to 93 and I loss power. Since then I only do the high test gas no exception. Curious why do 89 and not splurge for highest octane. Those premises u can buy are at least 92 octane or so

 

[Chris-PA]

87 octane E10 only.

 

[blsnelling]

99% of the saws I tune i set the idle with the L,back the idle screw out so it's not touching and then tune it.

That would suggest an air leak or other carb issue to me. In my experience, with a properly tune L needle, backing the LA screw all the way out would allow it to die.

 

[jmssaws]

That would suggest an air leak or other carb issue to me. In my experience, with a properly tune L needle, backing the LA screw all the way out would allow it to die.

All the la does is open the butterfly which adds air and makes you add more L
I'm just cutting out the middleman.

 

[jmssaws]

Most every saw I tune is close to 1 and 1

 

[jmssaws]

To adjust the idle you either richen to slow or lean to speed up,most carbs can be tuned without the la.

I back it out to just touching

 

[Amp4027]

Hmm okay so I know my question has been answered. but in regards to last comment I do run 93 octane gas. On some of my saws I tried 87 and the tune was way off compared to 93 and I loss power. Since then I only do the high test gas no exception. Curious why do 89 and not splurge for highest octane. Those premises u can buy are at least 92 octane or so

Higher octane only gives more power if you have variable valve timing and a 12:1 or greater compression ratio. In those motors, 87oct would trip the knock sensor and retard the timing to keep it from detonating. More than likely, your saw needed a very slight carb retune to get running at top power output, since it was set with 93oct gas.

Contrary to popular belief, higher octane does not equal mo' powah. Octane rating has to do with the amount of additive they put in it to keep it from exploding by itself simply by pressure (or also in combination with heat), which really equals less power since its not as volatile. Top that off with what jmssaws said about higher octane gas sitting longer (since only German&sports cars need it, and even then, the owners don't want to pay an extra $0.45-0.60/gal for it and usually go with midgrade), and you more than likely getting old gas and ~0.5gal from the pump hose of 87 from the last guy who filled up for the price of 93, regardless.

If you run an Alaskan mill, or you got the dosh to run 93, then go for it. Luckily, a very busy local gas station stocks 89oct ethanol-free due to it being right next to a boat marina, so that is what I will run and what the manual calls for.

 

[MattG]

This is the first run and tune after porting,this is how I tune one.

This is nice, and whilst the saw sounds good, without any annotations as what he is doing and when, it is not helpful to any beginner who sets out to tune a saw. In my own opinion! Other people might have different view though....

For instance due to the distance saw to camera I could not see which way he moved the screws, or which screws he moved at any time. It also seemed difficult to follow by my old ears exactly how the engine was following the smaill adjustments he made.

I'm not trying to have an argument and I'm sure that you and cr500 know your stuff... but just giving feedback after I saw and listened to the clip.

 

[scheffa]

Higher octane only gives more power if you have variable valve timing and a 12:1 or greater compression ratio. In those motors, 87oct would trip the knock sensor and retard the timing to keep it from detonating. More than likely, your saw needed a very slight carb retune to get running at top power output, since it was set with 93oct gas.

Contrary to popular belief, higher octane does not equal mo' powah. Octane rating has to do with the amount of additive they put in it to keep it from exploding by itself simply by pressure (or also in combination with heat), which really equals less power since its not as volatile. Top that off with what jmssaws said about higher octane gas sitting longer (since only German&sports cars need it, and even then, the owners don't want to pay an extra $0.45-0.60/gal for it and usually go with midgrade), and you more than likely getting old gas and ~0.5gal from the pump hose of 87 from the last guy who filled up for the price of 93, regardless.

If you run an Alaskan mill, or you got the dosh to run 93, then go for it. Luckily, a very busy local gas station stocks 89oct ethanol-free due to it being right next to a boat marina, so that is what I will run and what the manual calls for.

Why would you suggest to run higher octane fuel in a mill??

 

[MattG]

Why would you suggest to run higher octane fuel in a mill??

Is not because high RON means higher auto-ignition temperatures? And does milling not imply longer WOT running therefore longer sustained high temperature?

I'm quoting from http://www.economist.com/blogs/babbage/2012/09/octane-ratings the following:

To prevent that happening, a high-compression engine uses a blend of hydrocarbons that is somewhat less combustible than normal. Ethanol has an auto-ignition temperature of 362ºC, while petrol bursts into flames without a spark between 246ºC and 280ºC, depending on the blend. Therefore, adding a little ethanol to petrol can raise the auto-ignition temperature enough to prevent the blend from igniting purely from the heat generated during compression.

PS I don't actually have a timber mill - so my response was just a theoretical thing... so go easy on flaming me!!!

 

[mdavlee]

Why would you suggest to run higher octane fuel in a mill??

That's what I'm wondering. I've milled a couple 1k bd ft with saws and only once or twice did I use anything besides 87.

 

[jmssaws]

Higher octane fuel will in theory keep cylinder Temps a little cooler.

I ported a 394 a couple weeks ago that after a little run time will diesel on 87
But it's high compression with a big ignition advance. Doesn't do it on 91

 

[jmssaws]

This is nice, and whilst the saw sounds good, without any annotations as what he is doing and when, it is not helpful to any beginner who sets out to tune a saw. In my own opinion! Other people might have different view though....

For instance due to the distance saw to camera I could not see which way he moved the screws, or which screws he moved at any time. It also seemed difficult to follow by my old ears exactly how the engine was following the smaill adjustments he made.

I'm not trying to have an argument and I'm sure that you and cr500 know your stuff... but just giving feedback after I saw and listened to the clip.

Wasn't meant to be instructional just how I tune one.
You should be able to hear it go lean then fat then how I set the high.

 

[jmssaws]

This is nice, and whilst the saw sounds good, without any annotations as what he is doing and when, it is not helpful to any beginner who sets out to tune a saw. In my own opinion! Other people might have different view though....

For instance due to the distance saw to camera I could not see which way he moved the screws, or which screws he moved at any time. It also seemed difficult to follow by my old ears exactly how the engine was following the smaill adjustments he made.

I'm not trying to have an argument and I'm sure that you and cr500 know your stuff... but just giving feedback after I saw and listened to the clip.

Cr500 is the guy who hired me to port his saw,he could know his stuff but he lives across the country so I don't know for sure.

 

[MattG]

I ported a 394 a couple weeks ago that after a little run time will diesel on 87

Out of interest... what did you mean when said "will diesel on"? Do you mean that you could tell that it was pre-igniting?

You should be able to hear it go lean then fat then how I set the high.

No worries, I'll listen to it again sometime... I guess you may not have had the leaned off L side revs climb that much before you went back to fat.

A sensitive L is generally not enough pop off pressure,I find that almost every wj on a 1122 could stand a few more lbs especially ported.

So with that 064 on the clip... had you firstly increased the POP? Did you shim the spring? etc. etc. Tell me more

 

[jmssaws]

After a hard cut the 394 won't shut off,it will run a second like a diesel.
Pre-ignition.

If you listen you can hear it lean out and get that hollow sound then it starts to surge then I go to the fat side. All in less than half a turn on the low. I started 1 and 1 and it tunes just a touch under 1 and 1 with the la just touching.

This saw has a very rare bing on it and needed no mods
I usually shim the spring because stretching it don't last very long

 

[MattG]

After a hard cut the 394 won't shut off,it will run a second like a diesel.

Nasty!

If you listen you can hear it lean out and get that hollow sound then it starts to surge then I go to the fat side. All in less than half a turn on the low. I started 1 and 1 and it tunes just a touch under 1 and 1 with the la just touching.

Yeah will listen again soon.

This saw has a very rare bing on it and needed no mods
I usually shim the spring because stretching it don't last very long

Mine's here
http://www.arboristsite.com/community/threads/064-repair-project.288335/page-2#post-5630784

What shim do you use? Describe thickness material or ebay link if you can....

thanks Dude

 

[Amp4027]

Ethanol has an auto-ignition temperature of 362ºC, while petrol bursts into flames without a spark between 246ºC and 280ºC, depending on the blend. Therefore, adding a little ethanol to petrol can raise the auto-ignition temperature enough to prevent the blend from igniting purely from the heat generated during compression.

That's news to me, good find. Maybe 87oct E10 is sufficient then, but remember how eth rots fuel lines and how easy it is for the ethanol to bind to water (shaking it vigorously has no effect on mix it back together with the gas) and then sink right to the bottom of the tank, leaving you with 87 oct. And who knows, perhaps the oct rating is figured in with the ethanol's anti-det properties taken into account already (so its ~85oct and E10)?
That is what I was implying with milling, extended WOT and very high cyl head temps. But if Stihl's only have ~7:1 compression ration, then maybe it isn't as high performance as I originally thought (11:1+).

I'll listen to it again sometime...

I found this guy's vid was very very informative

On smaller saws like a tophandle, the burble is much more subtle and harder to listen for. 3:53-3:58 is what you need to listen for.
3:57.5 is where it changes over to 4-stroke.

This saw has a very rare bing on it and needed no mods

Can you inform us unfamiliar ppl what a bing is?