Stihl 084 starter kick back

[rwkbiker]

Help. I have had this Stihl 084 for 15+ years. Installed new Stihl piston and cylinder about a dozen years ago. Ran very well. In 2011, it stopped firing. Installed new flywheel (1124 400 1200), new coil (2 204 222 114) and new trigger (1118 400 1001). Saw performed really well until recently - started kicking back when cranking. Reset coil air gap to .008 - no improvement. With each rope pull, kick back occurs first time piston nears tdc. Kick back is very violent - just broke second rope. Firing shuts decompression valve, unable to apply enough force to hold decompression valve open. Woodruff key, crank and flywheel appear perfect .

Any ideas re cause and fix?

 

[huskihl]

Flywheel key may be sheared

 

[Robin Wood]

what kind of coil PN is that, it usually ends with 1308 for unlimited and 1305 for limited and they might have different limited models. and flywheel has 2 slot X and P i think. try switching over and see if helps

 

[briguy26]

Like huskihl said, check flywheel key. I had this problem with my ms661. It would backfire through the carb. When I looked at the key it appeared still intact but it was totally sheared off when I took the flywheel off. Good luck

 

[davidtown]

Any chance you have fuel in the cylinder? Fuel leaking out of the muffler?

 

[rwkbiker]

Thanks for the feedback. Answers :
1) Best I can tell - woodruff key, slot in crankshaft and flywheel appear perfect. Flywheel only has one slot.
2) Coil Bosch - 2 204 222 114 - I worked with local Stihl dealer in 2011, when I selected and installed these parts. I understood this coil to be same as 1124 400 1305.
3) No hydraulic lock or flooding.

Additional info - no kick back until maybe a year ago. Began very rare - now it's almost every pull. Can't express how violent kick back is. I use heavy leather gloves when attempting to cranking it. I have enough hand grip that the Stihl rope grip / handle folded as rope pulled it between fingers.
Rope is about 40" long. If I pull rope slowly to full length, kick back only occurs first time piston goes thru tdc.

Could a bad coil or trigger be the cause ?

 

[davidtown]

Does taking the coil off make a difference? Taking the flywheel off make a difference in the violence?

 

[Robin Wood]

just spoke to my dealer he said limited coil tends to advance when nearing failure, you can try the 2 slot flywheel or new coil. just a thought if you've bump into a wall

 

[rwkbiker]

Does taking the coil off make a difference? Taking the flywheel off make a difference in the violence?

Not sure I follow your logic. There is no kick back with coil removed or ignition off. Starter rope can't spin crankshaft without flywheel installed. The kick back is the cylinder/piston firing before piston reaching top dead center - spinning crankshaft backwards.

A good challenge is fun, but I'm ready for this one to be resolved and back to enjoying an awesome saw! I love running it with 30" bar. Just fell and bucked a large standing dead red oak - diameter greater than bar length until 40+ feet up. I'll be splitting it into firewood by hand tomorrow. But still need saw running to cut the stump.

 

[rwkbiker]

Not sure I follow your logic. There is no kick back with coil removed or ignition off. Starter rope can't spin crankshaft without flywheel installed. The kick back is the cylinder/piston firing before piston reaching top dead center - spinning crankshaft backwards.

A good challenge is fun, but I'm ready for this one to be resolved and back to enjoying an awesome saw! I love running it with 30" bar. Just fell and bucked a large standing dead red oak - diameter greater than bar length until 40+ feet up. I'll be splitting it into firewood by hand tomorrow. But still need saw running to cut the stump.

Not sure I follow your logic. There is no kick back with coil removed or ignition off. Starter rope can't spin crankshaft without flywheel installed. The kick back is the cylinder/piston firing before piston reaching top dead center - spinning crankshaft backwards.

A good challenge is fun, but I'm ready for this one to be resolved and back to enjoying an awesome saw! I love running it with 30" bar. Just fell and bucked a large standing dead red oak - diameter greater than bar length until 40+ feet up. I'll be splitting it into firewood by hand tomorrow. But still need saw running to cut the stump.

Not sure I follow your logic. There is no kick back with coil removed or ignition off. Starter rope can't spin crankshaft without flywheel installed. The kick back is the cylinder/piston firing before piston reaching top dead center - spinning crankshaft backwards.

A good challenge is fun, but I'm ready for this one to be resolved and back to enjoying an awesome saw! I love running it with 30" bar. Just fell and bucked a large standing dead red oak - diameter greater than bar length until 40+ feet up. I'll be splitting it into firewood by hand tomorrow. But still need saw running to cut the stump.

 

[rwkbiker]

Thanks Robin, that would explain its behavior.

 

[davidtown]

Complete hand to face comment on the flywheel thing.

More trying to eliminate the issues. I'll bow out now. Good luck

 

[HarleyT]

Sounds like excessive carbon buildup in the combustion chamber.

 

[rwkbiker]

I've not pulled cylinder and piston to check for carbon. Muffler is clean. I only use Stihl oil.

Two additional points:
1) once started, it runs well and strong.
2) Kick back is same whether saw is stone cold or hot.

 

[Robin Wood]

if my dealer is right about the coil advancing part it should run stronger than usual because advance timing improves power
1 trick to deal with this is to hold the decomp down while starting and releasing once its started
cs1201 has decomp lock where its locked before starting, im guessing its ignition is advanced in stock form.
hope you dont rip your arms out, i hate getting bitten by 084 or 1200/1201 they hurt real bad

 

[HarleyT]

I've not pulled cylinder and piston to check for carbon. Muffler is clean. I only use Stihl oil.

Two additional points:
1) once started, it runs well and strong.
2) Kick back is same whether saw is stone cold or hot.

Yes, it should run better with the carbon buildup.

 

[Old2stroke]

Something has caused your timing to be advanced. As stated above, your coil has probably gone sour. Is your flywheel a solid piece of aluminum or does it have a steel center part that fits on the crankshaft? A forum member recently had the center part twist with respect to the rest of the flywheel, causing the timing to be way off. It was a plastic flywheel but I have also seen the same construction on metal flywheels. If this is the case, it would explain why the timing got progressively worse as the center hub slipped a bit at a time.

 

[rwkbiker]

Thanks. I'll start search for a coil, and check for carbon. I think a person would have to experience the kick back to believe the magnitude.

 

[rwkbiker]

Flywheel has steel center. Thanks for that insight.

 

[rwkbiker]

I went to local Stihl dealer - shared problem and existing part numbers. They were sure coil 1124 400 1308 was available for $130 but not sure of possible working combinations. So, I called Stihl HQ and spoke with tech. Detailed problem. They were confident coil was the problem. Two techs studied situation and researched progressive changes Stihl had made to 084 thru the years. Results: Coil 1124 400 1308 supersedes previous versions, is available, does not require a trigger, and is compatible with single key 1124 400 1200 flywheel.

Note: Techs confirmed flywheel and trigger no longer available.

I plan to order coil from local dealer 2-7-2019.