stihl 361 bogs down after it heats up

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adnimo

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Hi, my Stihl 361 begins to act as if it's too rich once it heats up after a few minutes of use. What happens is it finally chokes up and dies and it's very hard to start it up while it's hot, in fact I have to wait until it's cool again and then it starts on second pull.

I checked for leaks around the carb and I couldn't find any, other than that the sparkplug has been replaced twice I flushed the lines and made sure they were not damaged. What could be wrong?, cracked case?, bearings?, help anyone?

Just to clarify as it heats up it begins to rev itself up ever so slightly until it chokes off, I can keep it running by accelerating (so is it running rich or lean during this process?) but if I let go it shuts down.

It's only a year old and Ive taken good care of it in fact it looks brand new. What should I try next?

The reason I think it's running very rich during this process is because of the smoke I get from the exhaust as I rev it up. My mix is the usual and runs fine on all my other equipment.
 

adnimo

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Sounds like your saw is leaning out, not going rich.

Alright, but what could be the cause?

Impulse seems fine so I'm shooting in the dark right now hence why I registered to ask around since I've been roaming the forums for a long while but never registered because I simply enjoyed reading the topics and had nothing to add since I'm not an expert perse.

The key here is that it only happens as it heats up otherwise when cold it runs great until a few minutes after where it warmed up and refuses to even start after it "leans out" to death.

Since it's leaning I'm even more worried now because I could damage the top end if I keep using it as is
 

Zippy

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You're right that smoke is often a sign of being rich but revving is definitely a sign of being lean.

Are the H and L screws set around where you expect - about a turn out?

Could pull the muffler off and quick check piston and rings look ok.

If it's happening after a couple of minutes it could be vac building in your tank starving the carb of fuel. If you open the cap when it stops does it hiss?

You could check the fuel line for crack/splits in case it's drawing in air but can't see why this would start when warm - sometimes ok with a full tank but starts as the tank empties.

Check the fuel filter isn't blocked?

You could pressure/vac check the saw whilst still warm (might be difficult) to see if it's still airtight.

Impulse line as has already been said.

Then I think you're into checking the carb - see if the metering lever is set right, diaphragms and gaskets ok, clean orifices etc.

Good luck.
 

adnimo

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The L and H are set about right, in fact the saw is tuned pretty well and it cleans nicely on the cut while it 4 strokes when unloaded which is what I've read to be a good sign (set it a bit rich after you find that point is another pointer I've been given)

I don't know how to vac check a saw, do I need special equipment?

Fuel filter looks tinted with the colour of the 2 stroke oil I use but other than that it doesn't seem clogged and all the lines are nice and flexible. I don't have a dealer nearby as to buy a set of new lines though but if that's a probably culprit (even though I see no leaks and they feel right) I'll try to buy new ones.

When the saw is not in use I purge all the fuel and let it run dry, I do leave the bar oil inside but that's irrelevant to the engine I would imagine. I also clean it thoroughly after a couple uses. The gasoline we use doesn't have ethanol in it.

Carb looks clean when you half disassemble it but I might have to take it all apart and put it in a bath of fuel or some cleaner solution?, So I have to replace the gasket for the carb if I open it? what about the gaskets that seal it to the engine?

Is it a good idea to use shop air to blow clean a carb or does it make things worse?

Sometimes when I open the gas cap it does hiss a little, but it's always done that. Is there a check valve somewhere I need to test or replace?

Thanks y'all!
 

Zippy

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Agree - pressure/vac test.

When I read the original post I thought he'd done that - checked for leak around carb - but guess that was fuel leaks. That's why I suggested to try it when it's hot and the fault is showing.

Also check piston/ring condition.

Try and run it after you've cracked the gas tank cap to clear any vacuum.

Normally if you remove the gaskets from the carb carefully you'll be able to reuse them if they're ok.

Don't know the 361 but don't think there's a gasket to the carb boot - just rings inside/outside the rubber boot.
 
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