I have an ms291 that will not start. It was working fine then started acting like it was running out of gas/running lean so I went to put gas in but it wasn't empty. Carb and spark plug look good. Tried gas in the spark plug hole, still nothing. Checked the compression and it's only 90 psi (not sure how accurate my tester is). Looked in the exhaust port and nothing too crazy a slight score on the piston. Think the compression is my problem? The saw is only 3 years old.. used for a few hours every week. Any info would be great. Thanks
Ms291 not starting
- Thread starter Hantsman
- Start date
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Pull the muffler and see if the piston is scored.
see if the fuel filter is clogged up, you should be able to blow through it easily. If the fuel hose is weak and or the filter is plugged it will suck flat and run the saw lean. the intake boot will get torn and cause the same symptoms of no start/lean. I have found low compression saws will start and run if you hold the throttle wide open but not hold idle and spit fuel out of the carb with the air filter removed due to lower vacuum.
with the muffler off you can touch the rings to check for them being stuck or free by gently pushing them, a slight up and down movement of the piston will show you the ring gap in the lands. if it was run lean it will remove the spring temper in the rings and expand the piston until it rubs the cylinder wall transferring aluminum causing compression loss.
RED-85-Z51
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Sounds like the 291 and 391 on my bench...both smoked needing top ends
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The rings look stick, also seems to be a small chip out chip near the top of the piston. I'll have to pull the cylinder. Will a piston and ring replacement usually do the trick if the cylinder isn't too damaged?
sometimes a set of new rings and some scotch brite to remove aluminum from the cylinder wall plating will put you back to work, inspect every thing very carefully as you tear it down and rebuild the carb while your in there.
Pics when its apart.
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What did it hit?
carb screw??
carb screw??
- Joined
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I think that you need a cylinder too.
RED-85-Z51
Addicted to ArboristSite
OH Yeah...that top end is done
https://www.ebay.com/itm/363265840429?epid=1954098964&hash=item549454d52d:g:FdsAAOSwizpcaI4qunder 300 for a oem piston/cylinder, That saw ate something metal. I would check the wrist pin bearing for a missing needle if your carb is not missing a throttle plate screw. did you run it without the air filter or remove it in the field recently?
Close to 500 bucks by time time it gets go me in Canada, same price from a dealer here. I don't see anything missing parts and didn't have the air filter off. I am going to stick a cheap piston in it and see what happens. If it's a write off I'll buy a new saw. Possibly a ms261... I thought about trying a husky but I have a few bars I could use if I stick the same brand
I will eventually need a MS291 piston, too. So, I am interested in seeing what you end up with...and, how it works out. As you probably know, there are early- and late-versions of the piston.
Roy
Roy
So I sanded down the rough spot on the cylinder, installed a new piston kit and crank seals. The saw started right up and ran fine. Shut it off and now it won't start again. I had already bought a new ms261c which I like better anyways. Looks like the 291 might end up in the junk pile.
Actually I played around with the saw and got it going. Used it for about an hour today. Worked good. We will see how long it lasts
