Only way to know for certain.
What happened to my MS390?
- Thread starter a. palmer jr.
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You haven't just removed the muffler for a peek?
I just went out and removed the muffler and saw absolutely nothing that looked anything but new. The only thing possibly was that maybe the rings hadn't seated. Maybe the first guy was right in that they didn't put a round piston in a round cylinder. Anyway, no scratches on piston or bore (what I could see of it). By the way, I found a deal on some Caber rings for the 390 and ordered them. I checked the de-comp valve plug and it looked okay. I imagine that when it warms up a bit around here I'll pull the engine and get a closer look...
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So it won't start at all?
No, it does just like an engine with 90 compression would. A friend of mine said to squirt some two stroke oil on top of the piston and that might raise compression enough to get it going, then just run it until the rings run in.. He says he's started lots of them that way. I tried this on a Weed Eater leaf blower last year and it worked. One thing I might mention about the starting: I'm a little older than many folks on here (76) and have a heart condition so I can't pull quite as hard or as long as the younger guys but I still can get my other 390 started with no problem...
like I have already said put some oil in the sparkplug hole , about a table spoon full , it may have flooded and washed the rings off
I put a little oil in the hole today but probably not enough, didn't seem to raise compression much. I'll do it again tomorrow and see if it'll do anything...On all the others all I had to do was liberally coat the rings with oil during assembly and that was enough. Maybe this engine has more p/c clearance than the others did...
you have to add enough to cover the entire piston , I bet it will start and run if you don't have a carb issue and I think maybe you do
I have a new carburetor but have been holding off because of getting too much money in the saw. Owner told me it ran before with the old carb on it but I hear that a lot...I may take that carb apart and see what it looks like inside if it doesn't start...
Lark-o
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Check the flywheel. I just did one where the flywheel didn’t sit on the taper very well. It never gripped the taper and it stripped out the casted in key on the flywheel. Ran great for 1 tank than it just quit. Pulled over like it didn’t have a plug in it.
Thats what I was telling you from the start do a compression test.
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Yeah, definitely check the flywheel key.
If that is the problem, run the saw a bit, then check your compression.
If that is the problem, run the saw a bit, then check your compression.
I could tell without doing the test that the compression was low. The rope was too easy to pull.
Rip it down.
That's the next thing on the list. Fighting the flu and the cold weather around here, working on saws in between. Funny they don't bring me many saws in the Summer...
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Actually, I've been working in the living room on the coffee table with a large piece of cardboard under it. I just checked the flywheel and it's okay...looks like we may be back to excessive clearance on the piston, cylinder. I tried starting it a few minutes ago and it's still a no go...the engine does have spark also..
I don't know what to take a pic of, my camera isn't sharp enough to check clearances on the engine which I suspect is the problem.. Just for the heck of it I may get out today and mix up some new fuel and try it...
Getting ready to order some more parts for it later today.
