MS170 will not start

[G4TRA]

I guess that this has been discussed many times before on here, but here goes.

 

My old Stihl MS170 wont start after eight weeks from when it was last used. I use the recommended full choke till it fires once,  then half choke to start method. Always seemed to start OK before, but now she wont even fire once.

 

I have done the following:

1. Pulled the plug, there is plenty of spark there. Both using an in-line spark detector and observing the plug gap

2. The plug is wet, indicating fuel is getting in.

3. I have changed the fuel.

4. Tried Quick start down the plug and onto the top of the piston.

5. Cleaned the air filter.

6. Checked that the choke flap is being operated.

 

The only thing I haven't done is remove the carb, but as there is plenty of "wet" on the plug I think fuel is being injected into the cylinder and as such I would at least expect it to fire. 

 

Can any one assist please?

 

Steve

 

 

[ChrisNewport]

If youve spark and fuel its compression. Remove the exhaust and check the state of the piston.

[muttley9050]

My first thing everytime would g be to change the plug for a new one, just because it's sparking out of the cylinder doesnt mean its sparking in the cylinder

[muttley9050]

I guess that this has been discussed many times before on here, but here goes.

 

My old Stihl MS170 wont start after eight weeks from when it was last used. I use the recommended full choke till it fires once,  then half choke to start method. Always seemed to start OK before, but now she wont even fire once.

 

I have done the following:

1. Pulled the plug, there is plenty of spark there. Both using an in-line spark detector and observing the plug gap

2. The plug is wet, indicating fuel is getting in.

3. I have changed the fuel.

4. Tried Quick start down the plug and onto the top of the piston.

5. Cleaned the air filter.

6. Checked that the choke flap is being operated.

 

The only thing I haven't done is remove the carb, but as there is plenty of "wet" on the plug I think fuel is being injected into the cylinder and as such I would at least expect it to fire. 

 

Can any one assist please?

 

Steve

 
 

Always worth doing a tea spoon of fuel into cylinder to. If it doesn't fire on that then I assume either no spark or no compression.

[spudulike]

You need to check the compression or pull the muffler and look at the piston unless you have enough experience to KNOW it is good.

If the compression is OK, pull the plug, turn the saw upside down, pull the saw over hard to clear any unburnt fuel, try heating the plug up on a gas stove or using a plumbers lamp, refit, don't use any choke, open the throttle fully and pull the saw over hard - a bit redneck but it may clear the issue.

You have probably missed the first pop of the saw and flooded it when you tried starting it.

[G4TRA]

Thanks for the replies so far. 

I have pulled the muffler off and the piston appears smooth and unscored. 

What should the compression be? I have a compression gauge and fitments to test it.

I will change the plug over from a good working unit, warm it up and try that.

 

[openspaceman]

3 hours ago, muttley9050 said:

Always worth doing a tea spoon of fuel into cylinder

Not that much, no more than a couple of drops into the carb I find.

[spudulike]

150-170psi....if the plug is wet, more fuel will not help!

[spudulike]

Probably just flooded, dry it out as previously stated and try again.

[G4TRA]

Thanks for all your assistance guys. I did as Spudulike suggested, removed the plug, cleaned it off, reversed the saw and pulled the starter half a dozen times to clear fuel in the cylinder. After putting the plug back in, she fired first pull on full choke. Put her to half choke and she started and ran second pull. Result!

She now starts and runs perfectly and I know where to come if I have any more problems with my raft of Sthil machines in the garden shed :o)