Stihl MS 180c won't start after lunch

[barker7]

I've owned my MS 180c for about 15 years and used it mostly for tree trimming. Today, I started with a full tank and used it for about an hour cutting up fallen limbs 2-5" in diameter. Freshly sharpened, and with a new plug and air filter, it cut great.

I took a 30 minute break for lunch, and then afterwards, it would not start. Took the plug out, dried it off and tried again. Repeated a few times. Not even a little blip.

1. Still has plenty of gas.
2. It has spark (checked by pulling the plug and resting it against the cylinder)
3. The plug is nearly new and correctly gapped. I tried the old plug too, with no better luck.
4. Cylinder is getting fuel (odor of gas on the plug)
5. It feels like there is normal compression when trying to start.

Any ideas what may be wrong or suggestions for further diagnosis?

Thanks much,

Mitch

 

[MACHINE]

Factory carb??

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[barker7]

Factory carb??

It's the original carb, so I presume it is a factory carb. Is there a way to identify?

I should clarify that the plug was actually damp with gas, not just smelled like gas

Mitch

 

[MACHINE]

How many adjustment screws on carb?

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[Nutball]

We have a 180 at work that seems to vapor lock, and it takes an unusually long time to clear (so I'm not 100% sure it is vapor lock). Using it hard for a while, then waiting a while (20min-1hr) can let heat soak into the carb and fuel line boiling the gas, filling the lines with vapor. Usually I can get it to fire via full choke, then if I'm lucky, it will stay running on half choke long enough for my to fiddle with the choke and throttle to keep the engine running long enough to work the vapor out of the system. I just don't understand how it can fire on full choke, then still take a good minute of continuous running to get it running right and not so starved for fuel it dies in the cut.

Maybe it is the quality of gasoline these days. Maybe the engine is wearing out, but I really don't think so. Maybe it is just a design flaw in the carb, and the 170/180 are known for not having good carbs.

If the engine is getting gas and good spark, but not running, it is either not getting enough gas, or it is getting too much. Putting way too much mix oil in the gas (like an extra bottle or 2) could cause it to not start, but it should still fire on full choke.

Try using starting fluid without using the choke, and if it fires on that, then you know it is not getting enough fuel. Note that it is easy to "flood" when using starting fluid, so it could take 10-20 pulls to for it to fire on starting fluid after a spray.

Take the exhaust outlet off the muffler and check the spark screen to see if it is completely plugged up with carbon. If so, toss the screen and put the muffler back together.

 

[MACHINE]

You can change the zama epa pos carb to a Walbro style, the diaphragm cover will interchange, then drill 3 adjustment holes in the saw to tune .

Gut muffler and tune it.

Makes saw much much better

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[Woodpecker]

None of my saws run after lunch either!

really makes the boss mad.



seriously though I would suspect vapor lock too. What was the ambient air temp when this happened?

 

[rogue60]

Sounds like it vapor locked and then you flooded it.
Hold the trigger WOT no choke if ever there is plenty of visible fuel on the plug.
I've got a few 170 180 and they all vapor lock in summer heat, ever since they have taken a lot of the anti boiling additives out of modern fuel that's no longer needed in fuel to run in new vehicles of today.

 

[Nutball]

It happened to me real bad on a 95degF day. I ran a whole tank through, refueled, and ended up having to pour gas in the air filter box, and using my hand covering the air filter to act as a choke. A major reason why I hate the Stihl combo choke/off switch, mainly because you get either full or half choke, and nothing in between.

 

[barker7]

Well, today it started. The circumstances of a hot day (~90), running for while, then sitting, do point to vapor lock.

Is it the fuel pump that gets vapor locked? the gas gets too warm so the pump is sucking vapor?

Thanks everyone. This is a great site.

 

[fearofpavement]

These saws are prone to the spark screen plugging up in the muffler. Make sure that's clean.

 

[MACHINE]

Another thing I do is modify the tank vent on them , I use a fuel line and Sthil fuel vent , those rubber tank vents suck

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