MS 084 AV

[Dan hensley]

Hello all!

First time poster here, however I have used this site and its many forms so many times. This has been so helpful over the years and usually with enough digging I can find exactly what I’m trying to trouble shoot with a saw!

This past year I received an ms 084 av from an older gentleman that happened to take notice of my love for all things forestry. According to the guy that saw had sat for 10 years at least. Well this year I finally got around to tearing into this big boy.

Findings

The good- upon inspection I have found a perfect OEM piston( still has machine marks) and cylinder. Compression tested out at 185 psi and I can start to understand why the old timer didn’t pick it up much in his last years of logging here in the mid west hardwoods. The spark seemed good visually, but I was concerned as I had read that the coils with an additional igniter module while unlimited a lot of times would give out more rapidly. The concern I had for the coil caused me to take it a step further and to test the resistance which checked out perfectly.

The bad- fuel line was rotted out from old gas and carb gummed up as well. Unfortunately this old hog lost its muffler apparently in the woods a few years before its retirement and now sports a piped exhaust which scares the crap out of me on a saw this big! Good buy some good ear plugs for the first time.

The ugly- I went ahead and pressure tested the saw and it had leaks yes leaks not just one. Both oil seals had gone bad and there was pass through from the crank case gasket into the oil tank.

So I split the case and put in a new gasket as well as a new cylinder gasket and new set of rings. I replaced the fuel lines, impulse hose, and put a carb kit in it. Put in new oil seals retested pressure and it tested out good. I went ahead and changed out the tank vent as well as I read the garb screw style have been know for trouble


Now I’ve been beating my head off of the work bench for about two weekends worth of work now from this next part. I put the carb to factory settings put in fresh fuel a little rich for break in 40:1 ams oil saber. Pushed in the decomp and pulled to eternity. Got zero fire so I finally put a shot fuel down the carb and BANG! She went. Burned up that fuel and died out. Went again shot down the pipe of fuel bang then dies out. I sat down on the bench tonight and watched the fuel line closely as it is a more see through line I installed. I’ve never experienced this before but every time I pull the saw over on choke the fuel starts to rise in the fuel line but then actually gets further away. When switched to just regular run and pulled over the fuel just sits still in the fuel line and doesn’t move. I believe it or not already had a spare OEM carb for an 084 parts saw so for ***** and gigs I swapped it out and yes it had a fresh carb kit in it as well. Unfortunately swapping the carb some I still am having the same problem. I don’t understand how this can be acting this way after all new rubbers and a carb rebuild kit has been installed amongst all the other things that I have done for the saw.
If someone can help me out with this one before I go insane I would greatly appreciate it!!!!!

Side not these are both the very first style of carbs offered on the ms 084

 

[Dan hensley]

Hello all!

First time poster here, however I have used this site and its many forms so many times. This has been so helpful over the years and usually with enough digging I can find exactly what I’m trying to trouble shoot with a saw!

This past year I received an ms 084 av from an older gentleman that happened to take notice of my love for all things forestry. According to the guy that saw had sat for 10 years at least. Well this year I finally got around to tearing into this big boy.

Findings

The good- upon inspection I have found a perfect OEM piston( still has machine marks) and cylinder. Compression tested out at 185 psi and I can start to understand why the old timer didn’t pick it up much in his last years of logging here in the mid west hardwoods. The spark seemed good visually, but I was concerned as I had read that the coils with an additional igniter module while unlimited a lot of times would give out more rapidly. The concern I had for the coil caused me to take it a step further and to test the resistance which checked out perfectly.

The bad- fuel line was rotted out from old gas and carb gummed up as well. Unfortunately this old hog lost its muffler apparently in the woods a few years before its retirement and now sports a piped exhaust which scares the crap out of me on a saw this big! Good buy some good ear plugs for the first time.

The ugly- I went ahead and pressure tested the saw and it had leaks yes leaks not just one. Both oil seals had gone bad and there was pass through from the crank case gasket into the oil tank.

So I split the case and put in a new gasket as well as a new cylinder gasket and new set of rings. I replaced the fuel lines, impulse hose, and put a carb kit in it. Put in new oil seals retested pressure and it tested out good. I went ahead and changed out the tank vent as well as I read the garb screw style have been know for trouble


Now I’ve been beating my head off of the work bench for about two weekends worth of work now from this next part. I put the carb to factory settings put in fresh fuel a little rich for break in 40:1 ams oil saber. Pushed in the decomp and pulled to eternity. Got zero fire so I finally put a shot fuel down the carb and BANG! She went. Burned up that fuel and died out. Went again shot down the pipe of fuel bang then dies out. I sat down on the bench tonight and watched the fuel line closely as it is a more see through line I installed. I’ve never experienced this before but every time I pull the saw over on choke the fuel starts to rise in the fuel line but then actually gets further away. When switched to just regular run and pulled over the fuel just sits still in the fuel line and doesn’t move. I believe it or not already had a spare OEM carb for an 084 parts saw so for ***** and gigs I swapped it out and yes it had a fresh carb kit in it as well. Unfortunately swapping the carb some I still am having the same problem. I don’t understand how this can be acting this way after all new rubbers and a carb rebuild kit has been installed amongst all the other things that I have done for the saw.
If someone can help me out with this one before I go insane I would greatly appreciate it!!!!!

Side not these are both the very first style of carbs offered on the ms 084

This is how far the fuel makes it

 

[cbfarmall]

Two questions: One, you sure it isn't sucking air somewhere along that fuel line? That would explain why it's having trouble lifting fuel. Two, how does someone 'lose' a muffler in the woods?

Is that blue stuff actual fuel line? What's in the tank?

 

[Bill G]

Good luck finding a muffler

 

[stihltech]

Again, get an OEM fuel line. But you also want to check the pump side of those carburetors.I would guess the pump diaphragm is not in correctly, corrosion on the carb, fuel filter not passing fuel well.
If you take the hose off the carburetor, fuel should push itself out the hose. If not, there is a leak of pressure somewhere. And what did you use for a vent hose? Those small screws are to slide into the hose, not SCREW in.

 

[Dan hensley]

Again, get an OEM fuel line. But you also want to check the pump side of those carburetors.I would guess the pump diaphragm is not in correctly, corrosion on the carb, fuel filter not passing fuel well.
If you tank the hose off the carburetor, fuel should push itself out the hose. If not, there is a leak of pressure somewhere. And what did you use for a vent hose. Those small screws are to slide into the hose, not SCREW in.

That’s the most frustrating part. As soon as I remove the fuel line it immediately sprays fuel halfway across my work bench. Thanks for the reply’s though guys

 

[stihltech]

Check the vent. If you used the same blue line, it may be plugged.

 

[Dan hensley]

Again, get an OEM fuel line. But you also want to check the pump side of those carburetors.I would guess the pump diaphragm is not in correctly, corrosion on the carb, fuel filter not passing fuel well.
If you take the hose off the carburetor, fuel should push itself out the hose. If not, there is a leak of pressure somewhere. And what did you use for a vent hose? Those small screws are to slide into the hose, not SCREW in.

Thank you for the reply! The fuel line shoots fuel halfway across my work bench when you take it off. As for the garb screw it was screwed into a old piece of hardened fuel type of line I replaced it with a new Stihl tank vent the small white almost fuel filter like type on a piece of OEM impulse hose and did a pressure/vac test through my actual fuel supply line works as it’s supposed to

 

[Mad Professor]

No reason to switch the tank vent system. The line with the grub screws were simple and effective, and cheap to repair. You can use generic fuel line for the vent if it's the correct size. As mentioned don't screw the screws in, push them.

You have a fuel delivery problem. Make sure the carb is assembled correctly: gaskets, diaphragm, covers, and the needle/lever is set/working properly.

P.S. we love pictures of old big saws........

 

[Dan hensley]

I’m going to take apart the carb and take pics of it broken down and put up the pics tonight. Maybe I’m just overlooking something and you guys will help me catch it! I’ll add in a few pics of the old beast as well. Also what’s everyone’s deal with bagging on my chouce of the fuel line? As long as it’s line that is rated for gas oil mix that is the exact same ID/OD and cut to the same length I’ve never had a single problem with replacing Stihl’s fancy OEM lines with something else.

 

[Mad Professor]

I’m going to take apart the carb and take pics of it broken down and put up the pics tonight. Maybe I’m just overlooking something and you guys will help me catch it! I’ll add in a few pics of the old beast as well. Also what’s everyone’s deal with bagging on my chouce of the fuel line? As long as it’s line that is rated for gas oil mix that is the exact same ID/OD and cut to the same length I’ve never had a single problem with replacing Stihl’s fancy OEM lines with something else.

Never owned a 084.

IPL shows TWO hoses with a connector. The one that goes into the tank is a molded one that would not be a good one to replace with tubing, use OEM.

Your pictures show the upper one which connects to the carb. That seems to be generic straight walled hose. Good call on that one.

Did you replace them both? And what sort of gas filter?

 

[Wood Doctor]

Mad Professor said, "P.S. we love pictures of old big saws...."
-------------------------
Like his one, for instance:

I sold this one about 10 years ago to a logger in Australia who says he still uses it. Whale of a saw and it ran very well. OP should also install a new pickup body (fuel filter), but I imagine he has already done that.

 

[Dan hensley]

I only replaced the top half of the fuel line with generic fuel line. The bottom half of the fuel line that goes into the actual fuel tank is an OEM line with a fuel filter off of a 066 magnum. Attached are the pictures of the carburetor, and the way that I put it together on the diaphragm side. The metering lever is set level with the carburetor body surrounding it. The only thing that I could find is this weird hole on the side wall of the body of the carburetor, where it almost looks like it has been blown out, but then it still looks like the gasket creates enough of the seal that that wouldn’t be a problem, also, strangely on my back up carburetor, it has the same strange, almost blown out looking hole. Sidenote, I have sprayed every hole and jet I can find in this carburetor with carb cleaner and compressed air. The weird hole is in the last picture attached

 

[sean donato]

Some hammer head stuck something in the side to pry that cover off. The mating surfaces look rough on the pump side. I'd glass plates them, but nothing sticks out as obviously incorrect. Did you pressure test the carb, and check pop pressure? Reuse the old needle spring or the new one in the kit?

 

[Dan hensley]

Some hammer head stuck something in the side to pry that cover off. The mating surfaces look rough on the pump side. I'd glass plates them, but nothing sticks out as obviously incorrect. Did you pressure test the saw, and check pop pressure? Reuse the old needle spring or the new one in the kit?

I used the new spring from the kit. What I did was a pressure vac test leaving the top half of my fuel line hooked up to the carb then taking my mightyvac and hooking up to the other end of the fuel line. I Then pumped it and the pressure never actually popped off but hit almost 35 psi not sure what it was supposed to be as I have never had to do this before. I understand the purpose of the test just not sure what readings I would be looking for. I also switched to vac and it didn’t hold any pressure on the vacuum side. Now as for pressure/vac testing the saw (crank case & P/C) yes I made air tight blocks out of bike tire inner tube and had a plate to bolt them on with. The saw it’s self after installation of oil seals, case gasket, cylinder gasket is good to go on that test.

 

[stihltech]

Are you sure that the spark continues after the shutdown. Meaning it does not shut off before the saw dies.
We can all get frustrated at this point. Time to get the beverage of choice, walk away, and come back at a later time to start fresh.
As far as the choice of fuel line, NEVER in a shop. Been bit too many times.

 

[RedneckChainsawRepair]

To much water under the bridge for me to recall much anymore. GL. Even parts was rough back then.

Owned 5 of the 84's . Was my fav work saw stock and ported with short and long bars.

Sold them off starting around 2010.

 

[sean donato]

I used the new spring from the kit. What I did was a pressure vac test leaving the top half of my fuel line hooked up to the carb then taking my mightyvac and hooking up to the other end of the fuel line. I Then pumped it and the pressure never actually popped off but hit almost 35 psi not sure what it was supposed to be as I have never had to do this before. I understand the purpose of the test just not sure what readings I would be looking for. I also switched to vac and it didn’t hold any pressure on the vacuum side. Now as for pressure/vac testing the saw (crank case & P/C) yes I made air tight blocks out of bike tire inner tube and had a plate to bolt them on with. The saw it’s self after installation of oil seals, case gasket, cylinder gasket is good to go on that test.

Pop pressure testing is done "wet" needs fuel in the carb to check it right and the metering plate/diaphragm needs removed. Should have popped long before 35psi. Like 10-15 psi ( @pioneerguy600 help me out here. Should be a tilly ht carb.)

 

[RedneckChainsawRepair]

Pop pressure testing is done "wet" needs fuel in the carb to check it right and the metering plate/diaphragm needs removed. Should have popped long before 35psi. Like 10-15 psi ( @pioneerguy600 help me out here. Should be a tilly ht carb.)

Tilley's HT 1 2 3 5 7 if I recall right.

 

[RedneckChainsawRepair]

Just in case. Pulling old info I have saved.

The coil part number 1124-400-1308 is no longer available starting sometime in 2010.

There are three ignition module produced for the 084:

1124-400-1305 Unlimited Ignition Module which requires the Trigger 1118 400 1001 (First Production)

1124-400-1306 Limited Ignition Module (Second Production)

1124-400-1308 Unlimited Ignition Module (Third Production)