Stihl 1123 Clamshell Leaks

[SteveSr]

Hello,

I have been fighting a weird issue with an old (pre-EPA) 025 (1123 series) saw. This was a homeowner saw that looks like it sat for years. The piston looks like a new saw. It tunes up and runs fine after a short warm-up. After a couple of buried bar cuts in 12-14" logs it starts to run noticeably leaner at WOT so I adjust the H screw a little bit. The idle speed also increases slightly so I back off on the LA adjustment. After the saw is completely heat soaked and warmed up the saw starts running noticeably rich at WOT and the idle speed drops to where it wants to stall.

Been through the carb twice and found a few issues but hasn't altered the above behavior. The impulse line has been replaced. Finally suspecting a weird air leak I removed the muffler and carb and installed blocking plates. Yes, I found a very slight air leak as follows:

Pressure 10 -> 5 PSI in 1:09 minutes
Vacuum 10 -> 5 in Hg in 0:35 minutes

Immediately suspecting the crank seals I hit it with some Windex on both seals and saw no bubbles under pressure. Today I came back with a Q-tip and soapy water. The water happened to flow past the seals and along the case seam and voila! there were bubbles on BOTH sides of the seam near the junction with the crank seal.

So it looks like I found the culpret! Stihl used some sort of white colored sealant which apparently has failed. So it looks like it is time for a complete teardown and new seals. Can anyone offer any tips to make this job easier and if I should use the red Dirko sealer or if you have found something better.

Thanks,

Steve

 

[brandonstc6]

Hello,

I have been fighting a weird issue with an old (pre-EPA) 025 (1123 series) saw. This was a homeowner saw that looks like it sat for years. The piston looks like a new saw. It tunes up and runs fine after a short warm-up. After a couple of buried bar cuts in 12-14" logs it starts to run noticeably leaner at WOT so I adjust the H screw a little bit. The idle speed also increases slightly so I back off on the LA adjustment. After the saw is completely heat soaked and warmed up the saw starts running noticeably rich at WOT and the idle speed drops to where it wants to stall.

Been through the carb twice and found a few issues but hasn't altered the above behavior. The impulse line has been replaced. Finally suspecting a weird air leak I removed the muffler and carb and installed blocking plates. Yes, I found a very slight air leak as follows:

Pressure 10 -> 5 PSI in 1:09 minutes
Vacuum 10 -> 5 in Hg in 0:35 minutes

Immediately suspecting the crank seals I hit it with some Windex on both seals and saw no bubbles under pressure. Today I came back with a Q-tip and soapy water. The water happened to flow past the seals and along the case seam and voila! there were bubbles on BOTH sides of the seam near the junction with the crank seal.

So it looks like I found the culpret! Stihl used some sort of white colored sealant which apparently has failed. So it looks like it is time for a complete teardown and new seals. Can anyone offer any tips to make this job easier and if I should use the red Dirko sealer or if you have found something better.

Thanks,

Steve

I'm not familiar but dirko should work if it is gasoline resistant. It's not too hard to disassemble. The impulse line is a little hard to put back on but hemeostats makes it easier. Be sure to replace the oil pickup line while you are at it too.


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[SteveSr]

I'm not familiar but dirko should work if it is gasoline resistant. It's not too hard to disassemble. The impulse line is a little hard to put back on but hemeostats makes it easier. Be sure to replace the oil pickup line while you are at it too.

The impulse line is much easier if the saw is already apart. The oil line is on t he list for replacement as well as the O-ring on the connector pipe.

Should this be reassembled with the sealant wet or should I wait for it to set and then carefully transfer the whole engine to the main case and put the screws back in? It looks like it would be difficult to do any other way as the cylinder and crank have to be angled and rotated to get the clutch side of the crank through the case.

Thanks,

Steve

 

[HarleyT]

That tiny of an air leak is not the cause of your problem, most likely it is in the carb.

 

[SteveSr]

That tiny of an air leak is not the cause of your problem, most likely it is in the carb.

Well, That's what I thought too. There is nothing that I haven't done to the carb (WT-215) except pull the welch plug over the idle circuit which I am hesitant to do as I don't have a tool to install a new one. I even changed the main nozzle/check valve which made no difference. What defect in the carb (@backhoelover carb expert) could cause the behavior noted?

I suspect that the leak gets considerably worse as the saw goes through the warmup cycle and then as the engine gets uniformly hot it pretty much seals itself up.

 

[alexcagle]

What does the intake skirt look like?

 

[windthrown]

The issue you describe is usually caused by a leak in the impulse line. I have had a LOT of 1123 saws, and several that were weird tuning/running were fixed simply by replacing the impulse line. That drives the fuel pump in the carb. A similar problem can happen if the carb is loose and impulse inlet is not sealed at the intake of the carb. Similar problems can also happen from wood chips or crud forming in the gas intake screen of the carb. I had that happen on my 211 saw where it was running funny, and I found that there was grey junk from the factory in the intake screen of the carb. I cleaned it out and it ran like a champ again.

 

[HarleyT]

#1123 120 0605 Walbro wt-215 costs $21.49 at the local Stihl dealer

 

[SteveSr]

#1123 120 0605 Walbro wt-215 costs $21.49 at the local Stihl dealer

Gee... I need to move back to Ohio to get this kind of pricing! Down here these are $40+!

 

[SteveSr]

The issue you describe is usually caused by a leak in the impulse line. I have had a LOT of 1123 saws, and several that were weird tuning/running were fixed simply by replacing the impulse line. That drives the fuel pump in the carb. A similar problem can happen if the carb is loose and impulse inlet is not sealed at the intake of the carb. Similar problems can also happen from wood chips or crud forming in the gas intake screen of the carb. I had that happen on my 211 saw where it was running funny, and I found that there was grey junk from the factory in the intake screen of the carb. I cleaned it out and it ran like a champ again.

The impulse hose is new. Everything else that you mention has been checked.

 

[SteveSr]

What does the intake skirt look like?

I haven't pulled the saw apart this far yet. I suspect that it is fine as the leak rate didn't change when flexing the intake boot.

 

[alexcagle]

I haven't pulled the saw apart this far yet. I suspect that it is fine as the leak rate didn't change when flexing the intake boot.

*
Na, that's not really what I'm talking about.
*
The intake skirt clearance and the condition of the chrome on the cylinder wall just below the intake port must be in good condition on a piston ported 2 stroke engine.
When the piston goes down and the intake skirt effectively closes the port,
it can't have excessive clearance, or the positive crankcase pressure will bleed back out through the carburetor as a spray.
If a little water gets ingested through the fuel supply at full throttle it can damage or strip off some of the chrome in streaks.
It won't mix with the oil in the fuel, so it can wash off lubrication off the cylinder wall.
It's not always easy to inspect that part of the cylinder without totally dissassembling the engine.
To test for this condition, (with the saw fully warmed up), take the air filter off, start the saw, and as you go from idle to full throttle in a quick burst, it will spray fuel back out of the carburetor. This is called "spit back", and as the saw gets hotter, it becomes worse from the increased clearance from expansion.
At idle the saw will load up.
Sometimes a malfuntioning carburetor can cause this same condition, so try a known good carb to rule it out.

 

[SteveSr]

*
Na, that's not really what I'm talking about.
*
The intake skirt clearance and the condition of the chrome on the cylinder wall just below the intake port must be in good condition on a piston ported 2 stroke engine.
When the piston goes down and the intake skirt effectively closes the port,
it can't have excessive clearance, or the positive crankcase pressure will bleed back out through the carburetor as a spray.
If a little water gets ingested through the fuel supply at full throttle it can damage or strip off some of the chrome in streaks.
It won't mix with the oil in the fuel, so it can wash off lubrication off the cylinder wall.
It's not always easy to inspect that part of the cylinder without totally dissassembling the engine.
To test for this condition, (with the saw fully warmed up), take the air filter off, start the saw, and as you go from idle to full throttle in a quick burst, it will spray fuel back out of the carburetor. This is called "spit back", and as the saw gets hotter, it becomes worse from the increased clearance from expansion.
At idle the saw will load up.
Sometimes a malfuntioning carburetor can cause this same condition, so try a known good carb to rule it out.

Thanks for the clarification! Since I found a leak I am going to fix it first and I now have a brand new spare carburetor. I still can't put my mind around what kind of carb defect could cause these symptoms.

 

[SteveSr]

What does the intake skirt look like?

The intake skirt looks excellent! Machine marks are still visible on both intake and exhaust sides of the piston.

 

[Brettl]

The intake skirt looks excellent! Machine marks are still visible on both intake and exhaust sides of the piston.

Following with interest! I have about a half dozen 025 and 250s waiting for their turn on the bench. What's the latest?

 

[redunshee]

You said the the sealant was white? bet it was rebuilt prior as I've always known Stihl to use Dirko HT.

 

[SteveSr]

The answer is... It appears that the leak was the source of the changing running characteristics at WOT previously noted.

I got a chance to run about 3 tanks through the saw this past weekend while cleaning out a creek bed of some nasty dirt covered trees. I was kind of surprised that the PM chain was still cutting pretty well at the end of the session. One vote for semi-chisel chain! The previously noted high end leaning-out at high temperature was gone. I checked multiple times after having the bar buried in red oak.

The only thing that I noted was the fine line of the "L" adjustment on the WT-215 carb. The idle speed seemed to increase after being run hard and would slow down again after the engine idled for a while and cooled off a bit. I an still not sure that it is set correctly. I think that I remember reading somewhere that the "L" should be set on the rich side of max idle speed setting point. Is this correct? If so, how much richer should I go and how do I know when I have got it right?

 

[tomdcoker]

Well, That's what I thought too. There is nothing that I haven't done to the carb (WT-215) except pull the welch plug over the idle circuit which I am hesitant to do as I don't have a tool to install a new one. I even changed the main nozzle/check valve which made no difference. What defect in the carb (@backhoelover carb expert) could cause the behavior noted?

I suspect that the leak gets considerably worse as the saw goes through the warmup cycle and then as the engine gets uniformly hot it pretty much seals itself up.

All you need to install a Welch plug is some fingernail polish for sealant and a 1/4 inch punch. Use the punch and a small hammer. One sharp rap on the plug until it has a dimple about 3/4 the diameter of the plug then put some fingernail polish around the edges. Let it dry before you get it in gas. Pressure test it if you have the equipment. I have rebuild probably 100 carb. and I think I have found one or two problems. I use chemtool carb. cleaner to check that the jets are open. Remove the low speed jet and squirt cleaner in the hole. Just be sure to have eye protection. There are 3 holes and there are bored at different angles. Tom

 

[SteveSr]

All you need to install a Welch plug is some fingernail polish for sealant and a 1/4 inch punch. Use the punch and a small hammer. One sharp rap on the plug until it has a dimple about 3/4 the diameter of the plug then put some fingernail polish around the edges.

Tom, Thanks for the info. However, welch plug sealant has been discontinued by *all* of the carb manufacturers due to issues with the current gas formulations containing ethanol which causes the sealant to dissolve and literally "gum up the works". Based on other threads on AS nail polish (nitrocellulose) is just as bad if not worse under these same conditions. Carburetor manufacturers have learned to improve their surface finishes and machining to properly seal metal-to-metal without sealants. These older carbs don't have that benefit.

 

[tomdcoker]

Tom, Thanks for the info. However, welch plug sealant has been discontinued by *all* of the carb manufacturers due to issues with the current gas formulations containing ethanol which causes the sealant to dissolve and literally "gum up the works". Based on other threads on AS nail polish (nitrocellulose) is just as bad if not worse under these same conditions. Carburetor manufacturers have learned to improve their surface finishes and machining to properly seal metal-to-metal without sealants. These older carbs don't have that benefit.

O K. I did not know that. Thanks. Tom