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Saw Diagnosis

Gypo Logger

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I took in a 395 cause it wouldnt run. The owner said he had rebuilt the carb and may have done it wrong. So that is what I zeroed in on, but after i rebuilt it there was no difference, just an intermittant pop.
So I removed the starter cover to check the coil and noticed the high tension lead was routed under the plastic face plate instead of on top where it should have been.
The flywheel wore a bare spot in the spark plug wire causing the intermitant spark.
Has anyone else been stumped by stuff that was misdiagnosed?
John
 

huskihl

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I yanked on my 066 after I ported it til I was blue in the face. Wouldn't start. Finally checked the flywheel key...sheared. Grabbed another key and did the same thing but only yanked for 10 minutes. Yep. Sheared again. Lapped the flywheel to the shaft and it did it again. Ended up pulling a fw off a carcass and used that one. Good to go now. Never seen a sheared fw key til then.
 

Warped5

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I don't see the misdiagnosed too often, but sometimes the trail to a correct diagnosis can be interesting ...

So I pull a really shiny MS391 out of a purchased lot, because I've never had one on the bench.

The tag said "Low compression" ....

I begin by removing the clutch cover. Lots of signs of excessive heat; tons of discolored plastic. The first clue is the spur sprocket with the DEEP grooves cut into it. Past that, the clutch is really discolored. Remove that and the end of the crank is bright blue!

So now I remove the muffler ... looks good!

Remove carb ... looks good!

So I get around to removing the cylinder ... it has just a tiny nick above one transfer. The rings aren't moving, because there's a gouge in the side of the piston. While I'm wondering what got in there, I see a piece of metal laying in the lower case ... a piece of a bearing cage!

All the heat on the PTO side caused by running an overmatched/neglected machine destroyed the cage. Piece flew around in the case until it got wedged on the side of the piston.

All this guy told me was how good he took care of his gear .... :facepalm:
 

SixGun

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Ms 460 ran great tuning on the ground and first few cuts, but then ran horrible after reaching up and trimming a tiny branch.
Turns out the intake boot actually dimpled in and blocked the intake! When held straight up the engine weight would crush it even more.
Replaced boot and buffers, great now
 

jacob j.

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We sold a brand new saw at the dealership, MS-440. My partner took it out back for its virgin start (customer, a local logger, was waiting in the lounge by our wood stove). It would pop but not stay running. He (my partner) came in and grabbed a small box off the parts shelf- it turned out that we had robbed the new carburetor off the saw a couple weeks prior and never replaced it. It was popping on the fuel that was spraying out of the fuel line. I initially thought it had a bad fuel filter or fuel line from factory, from listening to Bob monkey with it.
 

Mark71gtx

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I was recently given the task to finish a half hacked repair of a Stihl 420 cut off saw. The piston had some mild scoring (new P&C were replaced by the previous "mechanic") one intake boot had a hole in it, so I replaced it. I put it all back together. No spark. It needs a coil... Yes, it needed a new P&C and an intake boot - but, what caused it to stop working was the coil...
 

SixGun

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I was recently given the task to finish a half hacked repair of a Stihl 420 cut off saw. The piston had some mild scoring (new P&C were replaced by the previous "mechanic") one intake boot had a hole in it, so I replaced it. I put it all back together. No spark. It needs a coil... Yes, it needed a new P&C and an intake boot - but, what caused it to stop working was the coil...
Hi Mark, I have a coil if you need one off a ts400 it is part number- 4223 1302 . Coil was removed from a saw with bad top end so I am assuming it is good
 

Redfin

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I built a 44 for a buddy of mine. He wanted it as cheap as possible. I used oem bearings but aftermarket seals, intake and fuel line. The saw would sit and idle all day long but if you tried to pin it to wot it would bog and then eventually get there.

You could feather it to wot. I tried swapping carbs, coils. I went round and round with this thing till i finally saw the intake sucking shut.
 

Cut4fun

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I chased my tail on a 272 just a bit ago. Every diagnose you think that was common fix but still had the same problem. I finally tore the saw down and rebuilt from crankcase up.
Was a first for me. But fixed. :b1::dancer2::tmnt:
 

Mastermind

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Something to watch for on the 394/5, and the saws with the same coil.

I've seen several that wouldn't make good power......and just sounded off.

The coil gets stuck in the starting or retard mode. That means the ignition timing is way too low to ever run properly. If you encounter one of these that everything is good on......but it still just ain't right. Swap the coil from a known good runner.
 

Mark71gtx

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@Mastermind That name is still rather frequently mentioned in these parts! I live on the Harnett county side. Grew up in the big metropolis of Lillington. I now live in the Chalybeate Springs/Duncan/Christian Light area. Out in the woods, just like I like it. I have never lived anywhere that you didn't have to go down a dirt road to get there - and I intend to keep it that way!
 
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