Chainsaw repair

[Brian VT]

My b.i.l.'s MS360 Pro that he burned up and I volunteered to try to save him the $375 he was quoted to fix it.
I'm learning that there's truth to the saying "No good deed goes unpunished."
I cleaned up the cylinder and installed new piston and rings. It ran and cut okay but the idle would vary some so I decided to get a carb. rebuild kit. Before installing the kit I had a shop do a pressure test and he said the engine was tight. He didn't pressure test the carb. for some reason, though. So I cleaned up the carb. with air and spray and installed the kit and then I couldn't get it to run. I soaked the carb. overnight and now it runs. I didn't mess with the welch plug, fwiw. I think this saw sat for a bit with ethanol gas, fwiw.
LS and HS out 1 1/4 turns from full in (stops are cut off), nice plug color, 4-strokes for a second at WOT but then jumps to a scream (and I let off). The idle still varies a bit. It'll idle at one speed for 5-10 seconds and then drop to lower rpms for a while. Turning the saw on it's side(s) or upside down has no effect on idle.
I thought all was close to being well. Saw was warm and running as described. Now here's the kicker:
As soon as I touched the chain to a log the saw quit. I freaked and immediately checked the plug. It looked fine. No metal.
It started again fine and runs as described above with no load. I touched it to the log and it quit again. I did notice that the chain had stopped a moment before the engine was completely stopped, fwiw.
Do you have any clue what's up ?

 

[Gooserider]

For the idle issue, and general running, I'd try adding a slug of Sea Foam to the gas for a tank or two - it's easy to miss something when cleaning the carb, and the Sea Foam does a good job of getting the rest of any crud out.

On the part about getting killed when you put it under load, I'd suggest maybe looking at the brake / clutch, make sure there isn't something hanging up there somehow... Otherwise I have no idea.

Gooserider

 

[smokinj]

if its running really good out of the cut it sounds like the clutch

 

[dirttracker]

Did you check the fuel line for cracks? Sounds like you're getting just enough fuel to run the saw no load, but not enough to get any work out of it under load. I beleive the saw should 4-stroke a WOT indefinately, not just for a second or 2. This may be another indication of a fuel supply problem. You have enough fuel in the carb to run the saw WOT for a short period, but the fuel supply starts to go away after a short time at WOT and the saw goes lean and starts to scream. My MS 310 has acted this way a number of times, 1st time it was a rotten fuel line. The rest of the time I've found the impulse port on the carb was partially plugged. You may want to check the impulse line and port as well.

 

[Brian VT]

I was cutting with the saw before I messed with the carb. so I don't think it's a clutch issue.
dirttracker, your suggestions make sense to me. Thanks.
I plugged one end of the fuel line and blew into the other and I couldn't detect any leaks.
I sprayed carb. cleaner around the boot while the saw was running and couldn't detect any leaks there.
The only other thing I can do is change the fuel filter. I looks fine but I guess they're cheap enough that it's worth throwing one in.
The implulse line is clean. How do I check the port ?
I like the impulse port theory. Please help me diagnose that. Thanks.

 

[LLigetfa]

I was cutting with the saw before I messed with the carb. so I don't think it's a clutch issue...

Ja, sounds like a carb issue... either running too lean or starving for fuel.

 

[dirttracker]

To check the fuel line, stretch it out and look for cracks. You may have a crack that is opening up when the carb is installed, but closes up otherwise. I've heard (and seen on both my MS310 and 360 PRO) the fuel line is a common problem with Stihl after 4-5 years, so check it carefully. If you're going to put a fuel filter on, you may want to change the fuel line anyway. IIRC they are cheap, you should be able to get a new line and filter for less than $20.

What I call the impulse port is the metal tube coming from the cover on the underside of the carb. This tube has a right angle bend after it comes out of the lower cover. Mine will plug near the right angle bend in the metal tube. I take a small torch tip cleaner and run through the tube a few time then blow out with compressed air. I suspect in my case there is some crud built up in the rubber impulse line that eventually makes it's way into the metal tube. I really need to get a new impluse line and a carb kit in this thing when I stop cutting for the summer.

It sounds like the saw cut ok after the rebuild but before you put the carb kit in. If its not the impulse port, you've probably got a bit of crud stuck somewhere in the fuel passages or in the H side circuit on the carb.

What killed the saw in the first place?

 

[Brian VT]

What killed the saw in the first place?

I wish I knew. I think they're "old school" and kinda expect things to run when they pick them up, even if they've been sitting for 8 months.
Ethanol and the EPA has caused a lot of problems for those types.
I figured it was bad gas or a lean setting and a new top end and richening the HS would be the end of it.
Thanks for the advice. I'll grab a fuel line and filter and probe that elbow. Maybe try the Seafoam if that doesn't work, though I don't know if I dare run it long enough for it to have an effect.
They're coming up here this weekend. If I don't have it solved I'll hang my head and send him home with it as is and admit failure. I wouldn't even feel right asking for the $75 I've got into it.

 

[dirttracker]

Ya, its funny how things like this always seem more difficult on equipment that belongs to someone else. I suspect you are getting into the reason the saw roasted, keep after it and you'll find it. You might want to look over at aboristsite.com as well. There might be more help in the chainsaw forum if you can wade through all the posts.

I doubt you will cause any harm to the saw if you run it no load with the sea foam, but don't run WOT if its screaming.

Good luck.

 

[taxidermist]

You said you cleaned up the cyl. was it a failer do to lean out on the exaust side of the pistion? Does the cyl. have any scoring above the transfer ports? Did you compression test it? Tight from a pressure test means good seals not good compression.


Rob

 

[Brian VT]

The exhaust side had the worst of it.
The cylinder cleaned up pretty well with muriatic acid and some 600 w/d sandpaper.
My buddy at a motorcycle/sled shop looked at it and said it was good to go before I reassembled.
Pics here: http://s388.photobucket.com/albums/oo329/BrianVT16/Misc/

Got a fuel line and filter today. $18. I hope it's that or the impulse elbow.

 

[taxidermist]

Do yourself a favor before you put on the $18 worth of parts and do a compresson test. If you could catch a nail in the scratches you will have enough compression to run but not to run under a load. I had a 361 that did the same thing. I did the acid clean up ball honed it and put it all back together with a new pistion and rings and it had low compression. I then just bought a new jug for it and it runs like a top.


Rob

 

[Brian VT]

I couldn't feel or catch a nail where the cylinder scratches were. I'll try to check the compression.
What would you consider minimum compression (cold) ?

 

[taxidermist]

145-160 use a comp tester with a schrader valve in the end(valvestem) pull over till the pressure stops climing and then read.

 

[Brian VT]

I have an old Snap-On with a bunch of plug thread fittings. Why the shrader valve type ?

 

[taxidermist]

I have an old Snap-On with a bunch of plug thread fittings. Why the shrader valve type ?

Look here...... http://www.arboristsite.com/showthread.php?t=93600

 

[Brian VT]

Yup. Mine have that valve. Thanks. I read the whole thread while I was there.
I hooked it up to the saw and, with the decompression valve open, made sure it turned over okay. Clear.
I got it up to 150# and stopped when, for some reason, it sounded like the piston was rapping on the gauge insert.
Anyway, it looks like compression is okay so I'll check the impulse elbow and then throw the fuel filter/hose in and pray.
Thanks for all the replies. I appreciate all the support.

 

[taxidermist]

Any new news???

 

[Brian VT]

The impulse line and elbow are clean.
I put in the new fuel line and filter. It's no better.
I sprayed carb. cleaner around checking for leaks and can't determine any.
Here's a vid I just made:
http://s388.photobucket.com/albums/o...t=DSCN2881.flv
I'm stumped. I guess I'll hang my head and return it as-is.
It was suggested that I do a vacuum test on the case. I guess that would tell me if the crank seals were bad (they tested ok for pressure but maybe not vacuum).
I'm not sure I want to get into that or if I even have the tools needed to replace crank seals.
Thanks for all the help.

 

[smokinj]

Condition = Engine Speed drops quickly Under Load - Low Power.

Cause = Air Filter Plugged.

Remedy = Clean Air Filter.

Cause = Tank Vent faulty.

Remedy = Clean or replace Tank Vent if necessary.

Cause = Leak in Fuel Line between Tank and Fuel Pump.

Remedy = Seal or renew Connections and Fuel Line.

Cause = Pump Diaphragm damaged or fatigued.

Remedy = Fit new Pump Diaphragm.

Cause = Main Jet Bores or Ports blocked.

Remedy = Clean Bores or Ports.

Cause = Fuel Pickup Body dirty.

Remedy = Clean Pickup Body, fit new Filter.

Cause = Fuel Strainers dirty.

RemInfo from Carburetors Manual from Stihl.

Condition = Carburetor Floods; Engine Stalls.

Cause = Inlet needle not sealing. Foreign Matter in Valve Seat or
Cone damaged.

Remedy = Remove and clean or replace Inlet Needle, clean Fuel Tank, Pickup Body and Fuel Line if necessary.

Cause = Inlet Control Lever sticking on Spindle.

Remedy = Free off Inlet Control Lever.

Cause = Helical Spring not located on Nipple of Inlet Control Lever.

Remedy = Remove Inlet Control Lever and refit correctly.

Cause = Perforated Disc on Diaphragm is deformed and presses constantly against Inlet Control Lever.

Remedy = Fit new Metering Diaphragm.

Cause = Inlet Control Lever to high (relative to design position).

Remedy = Set Inlet Control Lever flush with top of Body, or bottom of the Metering Chambedy = Clean Fuel Strainers.

 

[Brian VT]

I've gone through the carb. more times than I can remember.
There could still be something wrong there but the only thing I would try at this point is putting on a know-to-be-good carb. to try
and I don't have access to one unless I bought a new one.
Air filter is new.

 

[taxidermist]

So when you rev it up with out it in the log everything feels normal? Has power ect. Then you place it on a log and it just dies? I cant get your vid? can you youtube it???

Rob

 

[Brian VT]

So when you rev it up with out it in the log everything feels normal? Has power ect. Then you place it on a log and it just dies?
Rob

Yup. Sorry 'bout the vid.