Saw fires & yanks starter handle out of my hand. Why?

[old-cat]

I think STIHL engineers are a bit on the STUPID side. ALL hand started engines should fire at TDC for start-up. Kick-back is caused by spark advance NOT compression!
I had a little wimpy MS250 with a kick-back issue one time. That thing would kick and the saw would go flying out of my grip and go rolling on the ground! I got so mad one time i threw the saw as far as I could!

 

[blsnelling]

Yeah, I've been bit My 084 will put a hurtin on ya if you forget to push the decomp.

 

[hotshot]

I think STIHL engineers are a bit on the STUPID side.

Engineering's always a compromise, and with these older fixed timing coils, they are selected to operate at the cutting RPM.

If they were set at 15° advanced for easier starting, instead of 26°, you'd be ******** about the lack of performance where
the tool actually operates.

What you need to do is come up with a cheap advance mechanism. like used on outboard boat motors
with till steering handles.

 

[old-cat]

Well the gurus here say the coil for 046 and MS460 is retarded for starting, why can't the rest of the saws be that way?????????????

 

[XSKIER]

Well the gurus here say the coil for 046 and MS460 is retarded for starting, why can't the rest of the saws be that way?????????????

It's called progress my dear. Why can't all saws have M-Tronic??????????????

 

[old-cat]

Economics, I suspect!

 

[slowp]

My saws just do that once in a while. Even when I push in the decomp button. I attribute it to demons that take possession of the saw. After several snappings of my arm, I usually set the saw down, say an incantation of original cussing, gently kick the saw, and go back to pulling on the starter cord. The 032 seems to have improved since having it worked on at the wunnerful saw shop we have. The Barbie Saw (440) just takes a notion and will do the snap of pain every once in a while. Such is the nature of the beasts.

 

[Chris-PA]

Well the gurus here say the coil for 046 and MS460 is retarded for starting, why can't the rest of the saws be that way?????????????

With points you'd need some sort of flyweight mechanical advance/retard mechanism. Or a retard lever (lol) or somesuch. That would add weight, cost and create another opportunity for failure. With an electronic ignition it is much easier, although they do have to bother to do it.

If it is different than otherwise similar saws then I'd bet the timing is off due to incorrect points set up.

Spark advance is not a complicated concept - it takes a more-or-less fixed amount of time for the mixture to burn, so at high rpms you need to start it sooner in terms of crankshaft degrees in order for cylinder pressure to peak at the right time (like ATDC so it can push the piston down). At slow cranking speeds that same number of degrees of advance is way too much, the mixture burns and the pressure peaks before the piston is a TDC. That kicks the piston backwards and rips your hand off.

 

[old-cat]

Your thoughts about ignition timing sound fine, but real live testing shows that gasoline wants approx. 25 degrees at ALL rpms for maximum power.

 

[Chris-PA]

Your thoughts about ignition timing sound fine, but real live testing shows that gasoline wants approx. 25 degrees at ALL rpms for maximum power.

I'm not sure where that figure comes from, but it's good to be cautious about "all" and "any". These rules are all oversimplifications and these systems only work over limited ranges, but we're talking here about hand cranking rpm - that's well below anything relevant to power output while the engine is running and what proper advance would be under those circumstances.

Otherwise, saws are only meant to run at WOT over a fairly narrow range of rpms, so it makes sense that a fixed timing advance should work fine.

 

[Agrarian]

To me it sure sounds like a timing issue. One thing that has not been questioned is the sparkplug gap. Could a narrower gap allow the spark to occur earlier since less voltage would be needed. The spark would then be generated earlier in the rotation.

 

[Chris-PA]

To me it sure sounds like a timing issue. One thing that has not been questioned is the sparkplug gap. Could a narrower gap allow the spark to occur earlier since less voltage would be needed. The spark would then be generated earlier in the rotation.

It doesn't really work that way - once the points open the voltage builds very quickly in the coil to what ever is needed to jump the gap. Yes, it will jump slightly earlier with a smaller plug gap but the time difference is small enough to be meaningless in these discussions.

The points gap matters a lot because it changes the angle at which they open.

 

[Jtheo]

I had the same thing on a Sacks Dolmar 143 with no decomp. It would numb my hand. Turned out to a coil problem.
It was a darn good saw, but at about 25 lbs loaded out to cut, I eventually got too light for the saw. Or as my Dad would say, I needed more lead in my a**.

 

[NewToStihl]

Thanks for all the tips guys! As soon as I get a chance (maybe this weekend) I'll start looking at 'key way play' and the points gap to see if it can be improved. I didn't know an improper gap could have this symptom.

I appreciate the help. Who says AS is dead!?!?

 

[NewToStihl]

Well, the weather & house projects kept me away from the shop for awhile but I finally had time to tinker with the saw today. The manual specifies the point gap at 0.012" - 0.016". Three times I started from scratch and set the gap at what I believe was right in the middle of that range, and the handle yank did not subside. I am certainly no too proud or arrogant to disregard the possibility that I'm screwing this up, but it seems pretty straightforward and simple so I'm inclined to think the gap is right.

Any other suggestions on the cause? Is there any other tweaking with the ignition system that could cause it if not the point gap?

 

[NewToStihl]

Bueller? Bueller?

Are there any potential benefits of (short term) opening the gap up above the specified range just to see if that eliminates the tug-of-war? I'm just thinking of ways to try & isolate the cause of the problem...

 

[strtspdlx]

You could try opening it up just enough to not give spark and then go back down. But opening it should retard timing and allow for easier starts. If it doesn't start any easier I'd look elsewhere.


Regards-Carlo

 

[Flat47]

My vote stays within the starting system, not ignition. If it's pulling the rope back in to the starter housing, the pawls or shoes are not disengaging fast enough. I've seen this lots of times on older saws that have sat and the pawls don't move 100% freely. I've also seen this on Rotax motors that use the steel pawls inside an aluminum hub. The springs get weak and the inside of the hub get worn and has burrs that keep the pawls engaged.

 

[HarleyT]

Y'all are just a bunch of girlie men

 

[Chainsaw Jim]

View attachment 449539

I wonder if ol aunt Bruce will endorse a gender bender potato head doll.