MS361 starting and dies

[Michael G]

Heres what I'm working with:

Fixed up this saw and had it running great. Couldn't tune it to stop chain at idle because I found clutch spring was broken.

New clutch in.

Now the saw just starts and dies. If I feather the throttle a little it will start alive. If I go WOT it dies. If I give it no throttle it dies. Sometimes it floods itself.

Originally I took the saw apart, replaced fuel lines, rebuilt and cleaned carb, bought a new carb to fiddle, visually inspected intake boot and impulse line.

Checked my seals by the turning it over method, and sprayed carb cleaned at the seals for good measure.

Only other things I can think of is putting the clutch in I lazily broke a flywheel fin, and that the saw has 2 drilled ports in the front of muffler.

Any help appreciates. I do not want to give up fixing this particular saw.

 

[Ozhoo]

Start my eliminating a ruptured fuel hose. Roll the saw on it's clutch side and start it... see what happens. Many a man has ruptured a fuel line while installing them.

 

[Michael G]

Start my eliminating a ruptured fuel hose. Roll the saw on it's clutch side and start it... see what happens. Many a man has ruptured a fuel line while installing them.

I started there, unfortunately. I took it out and rechecked the entire line. No pinholes, no breaks.

 

[Wood Doctor]

Could be low on compression. Test that next. Makes no difference what the carb or fuel lines are doing, if the saw is low on compression, it will never run right.

Quick compression test: try pulling the rope with the decomp valve pressed. Compare that with another pull with the decomp valve up. If there is hardly any difference, you are low on compression and need to rebuild the top end.

 

[Michael G]

Could be low on compression. Test that next. Makes no difference what the carb or fuel lines are doing, if the saw is low on compression, it will never run right.

Quick compression test: try pulling the rope with the decomp valve pressed. Compare that with another pull with the decomp valve up. If there is hardly any difference, you are low on compression and need to rebuild the top end.

Compression is a solid 160 psi cold. :l

 

[Whiskers]

Is the impulse line hooked up? If so, does it run with a squirt of fuel bypassing the carb? Did you ever pressure/vac test the saw?

 

[Wood Doctor]

Is the impulse line hooked up? If so, does it run with a squirt of fuel bypassing the carb? Did you ever pressure/vac test the saw?

Good point on the impulse line. That stopped an 025 that I have dead in its tracks. The carb is helpless without it. Take a look at post #28 here:
http://www.arboristsite.com/community/threads/pressure-testing.291159/page-2

 

[Van462]

Did you check the metering levers position when you rebuilt the carb? You mentioned you get flooding. So some fuel is making it thru the carb, If the metering lever is too high too much fuel comes thru and it too rich to start. Remove the spark plug and bring the piston to the very bottom. Flip the saw over and see if fuel comes out of the spark plug hole. if it does then too much fuel is moving thru and will pool in the crankcase. With the piston down the transfer ports should be open and allow it to flow out of the crankcase.
While the plug is out verify you have spark with the plug touching the cylinder.

The metering lever should be around .048 below level of the carb. Take the cover and gasket off and lay a flat edge use a feeler gauge to measure the gap, tweak the lever as needed.

You also mentioned a new clutch. Verify its operation by engaging the chain brake and ensuring the pulling the starter rope. With the plug still removed there should be little resistance.

Edit. You can also remove the flywheel nut and look to see if the crank keyway and flywheel groove are still lined up. i think its visible without removing the flywheel.

 

[Wood Doctor]

Did you check the metering levers position when you rebuilt the carb? You mentioned you get flooding. So some fuel is making it thru the carb, If the metering lever is too high too much fuel comes thru and it too rich to start. Remove the spark plug and bring the piston to the very bottom. Flip the saw over and see if fuel comes out of the spark plug hole. if it does then too much fuel is moving thru and will pool in the crankcase. With the piston down the transfer ports should be open and allow it to flow out of the crankcase.
While the plug is out verify you have spark with the plug touching the cylinder.

The metering lever should be around .048 below level of the carb. Take the cover and gasket off and lay a flat edge use a feeler gauge to measure the gap, tweak the lever as needed.

You also mentioned a new clutch. Verify its operation by engaging the chain brake and ensuring the pulling the starter rope. With the plug still removed there should be little resistance.

Edit. You can also remove the flywheel nut and look to see if the crank keyway and flywheel groove are still lined up. i think its visible without removing the flywheel.

Believe it or not, I have a brand new MS251C that is doing exactly that -- flooding much too easily and blowing fuel right out the muffler when I eventually get it to run for awhile. Then it can't idle. It has a good spark. No carb setting seems to mean anything. Limiters prevent much of a setting change. I can understand all this on a residential saw, but on a 361, it's indeed rare.

 

[Van462]

That is how I first noticed my issue. I noticed fuel coming out of my muffler. Pulled the muffler to find it had a nice puddle inside. Next I pulled the cylinder as it was a new saw build and found the crankcase flooded. I had set my metering lever to flush vs .048 below. It wasn't passing the logic test, I had fuel, fire and compression but it at most it would fire only enough to close the decompression release, barely enough to even hear.

 

[Wood Doctor]

That is how I first noticed my issue. I noticed fuel coming out of my muffler. Pulled the muffler to find it had a nice puddle inside. Next I pulled the cylinder as it was a new saw build and found the crankcase flooded. I had set my metering lever to flush vs .048 below. It wasn't passing the logic test, I had fuel, fire and compression but it at most it would fire only enough to close the decompression release, barely enough to even hear.

Well, as you know, the 251 has no decomp valve. When this saw does act like it fired on choke, you cannot hear any pop. So, it appears that it's getting far more fuel from the carb than it needs to run. I've tried a single pull on choke irrespective of noise, and it still floods out at the fast-idle setting.

You said, "Take the cover and gasket off and lay a flat edge use a feeler gauge to measure the gap, tweak the lever as needed."

Could you be more specific? What cover, gasket, and gap are you measuring? Pardon my ignorance. I would like to try this. Unless the dealer messed up the carb setcrews, I'm at the end of the rope.

 

[Van462]

Carb usually has 2 removable plates. Depending of the model of carb the plates will be held on by either corner screws or a center screw. If it has a screw in the center that is usually the fuel pump side. It receives the impulse to pump fuel to the metering side. On a 361 the metering side is the top. It is held by 4 screws. Remove it and the diaphram. Hopefully the gasket will come off in one piece. The diaphram actuates the metering lever. If it is set to high it actuates too early, too low and it actuates too late. With the gasket removed put a straight edge across the carb body and measure the gap between the lever and body. I don't know the spec for a 251 but I would see if its in the .030 to .050 range.

 

[Wood Doctor]

Carb usually has 2 removable plates. Depending of the model of carb the plates will be held on by either corner screws or a center screw. If it has a screw in the center that is usually the fuel pump side. It receives the impulse to pump fuel to the metering side. On a 361 the metering side is the top. It is held by 4 screws. Remove it and the diaphragm. Hopefully the gasket will come off in one piece. The diaphragm actuates the metering lever. If it is set to high it actuates too early, too low and it actuates too late. With the gasket removed put a straight edge across the carb body and measure the gap between the lever and body. I don't know the spec for a 251 but I would see if its in the .030 to .050 range.

Got it, and thanks a bunch. I'll check it tomorrow. Huge post by Van62 in my book. I have a feeling you isolated the real problem. My temporary "fix" thus far is to pull on choke only once after a prime. Don''t wait for a pop with more choke pulls because that won't happen and you will flood this engine. Move to fast idle immediately for the second or third cold-engine pull. Saw will probably start. It just did.

After that, I patiently tuned the carb for optimal performance, shut it off, and it started again on the first fast-idle pull. I'll see if it acts the same way tomorrow. Hard to believe that two choke pulls would flood an engine completely and no fast idle pulls would unflood it, but that's what I ran into with an almost-new saw.

My apologies to OP if I hijacked this thread. My MS361 is the saw I would keep if I had to sell them all and keep one.

 

[drf255]

I agree that it's likely the carb.

Check that the flywheel key didn't sheer as well. A quick and easy way is to pull the plug and make sure the piston is at TDC when the flywheel magnets line up with the coil leads.