Craftsman 316.791020 trimmer no start

[per4manz]

Needless to say, not very happy right now. Was trimming last week when the trimmer suddenly quit and wouldn't restart. To date I have done the following:

1. Checked fuel lines, filter and bulb. Had just changed them maybe a month ago at most.
2. Removed muffler, checked spark arestor screen and block port. No issues. Still wouldn't start with it off.
3. Tore carb apart and cleaned. All diaphragms in good condition and fuel inlet screen was cleaned. Remounted, but still no start.
4. Checked for spark. Seemed weak although plug was in great condition. Replaced with new plug, still no start
5. Still wasn't impressed with the spark strength, so ordered a new ignition coil. Installed yesterday. Made sure conductor gap was at .012. Better spark, but still no start.
6. Added small amount of fuel to engine cylinder via spark plug opening: still no start or even an attempt to start.
7. Added small amount of 2 cycle oil to engine cylinder. Held compression pretty well while pulling starter rope. Did notice that after several pulls that it became increasingly easier to pull. I feel like it is easier to pull than usual.
8. Tested kill switch. Operating properly.

Fuel isn't old and is properly mixed.

Am at my whits end. Would love to throw this thing away and get a Stihl or echo, etc., but really can't spare the money right now. Plus, I'm in an HOA subdivision, so I have to keep the yard maintained. Any help would be greatly appreciated.

 

[per4manz]

Update:

9. Just tried starting fluid. Still no attempt to even start.

 

[bertsmobile1]

Goes like this.
Dope squirted down carb throat & Spark tester on brand new plug.
Throttle wide open no choke.
If the engine does not go bang in 4 to 6 pulls you have either compression or timing problem.

next step is to remove muffler and inspect the bore.
Scratches in the bore, across the rings or down the piston = scrap metal.
If the cylinder & piston looks good repeat the test above sans muffler.

Engine goes bang = blocked muffler or restricted exhaust port.
Engine no go bang then remove the flywheel & check that the cast in key is intact.

After that all you are left with is the rings and crankcase seals which on most micro engines = scrap metal.

 

[per4manz]

Goes like this.
Dope squirted down carb throat & Spark tester on brand new plug.
Throttle wide open no choke.
If the engine does not go bang in 4 to 6 pulls you have either compression or timing problem.

next step is to remove muffler and inspect the bore.
Scratches in the bore, across the rings or down the piston = scrap metal.
If the cylinder & piston looks good repeat the test above sans muffler.

Engine goes bang = blocked muffler or restricted exhaust port.
Engine no go bang then remove the flywheel & check that the cast in key is intact.

After that all you are left with is the rings and crankcase seals which on most micro engines = scrap metal.

Thanks, Bert. I had already tested the muffler and associated ports. All were just fine. As I stated, still no attempt to start with it off.

What is the minimum compression required to start and stay running? I just tested it and didn't get above 50 psi and wouldn't hold it for long.

Additionally, this is a Speed Start model. I have noticed what seems to be premixed fuel in the crankcase behind the Speed Start apparatus. Am assuming at this point that the rings are blown and allowing the fuel mix into the crankcase.

 

[bertsmobile1]

Thanks, Bert. I had already tested the muffler and associated ports. All were just fine. As I stated, still no attempt to start with it off.

What is the minimum compression required to start and stay running? I just tested it and didn't get above 50 psi and wouldn't hold it for long.

Additionally, this is a Speed Start model. I have noticed what seems to be premixed fuel in the crankcase behind the Speed Start apparatus. Am assuming at this point that the rings are blown and allowing the fuel mix into the crankcase.

About double that figure .
However measuring compression pressure on micro engines is a lot more difficult than most would believe as the combustion chamber volume is not much more than 2 to 3 turns of the spark plug