Stihl 046 Revs hard when starting, then dies

[GrungyDungy]

Hey guys,
I know this is a topic that has been covered in several threads. rest assured I have read and re-read these posts. I have a Stihl 046 with a couple of seasons wear on it. When I start it on full choke, it sounds good, at half choke it revs high and then when I switch it up to run it revs very high(the sound isn't as deep as normal) and then dies unless I keep throttling it. I have replaced the fuel lines(both the main and the pulse line), replaced the manifold(that large diameter hose going between the carburetor and the cylinder), replaced the fuel filter, replaced the fuel tank vent, replaced the gas cap, cleaned the carburetor and then put a new one on, checked compression(it's great), tightened down all screws holding the crankcase together, and finally put a new tank housing on(the old one had been some exterior melting from a fire, although the inside looked smooth and undamaged). All to no avail. No perceptible change in how it starts or runs. i'm at my wits end, but I refuse to walk away from this saw. Any advice(besides getting a new saw) would be appreciated.

 

[watsonr]

Sounds like low idle circuit is plugged. Did you clean under the Welsh plug, try blowing carb cleaner thru the low side by removing the needle and watching the cleaner shoot out the opening inside the venturi. Screw the needle all the way in and then out one turn and try again.

Lastly, did you check for an air leak? You may have a seal going bad. Does the low side have any effect when you adjust it richer?

 

[lumberjack48]

Head gasket or crank seals

 

[GrungyDungy]

Thank you for the help. I was hoping not to have to seperate the crankcase, but I may just have to if it is that Gasket. it looks new, but i'm running out of options. When you say crank seals, are you talking about the cover that goes over the ball bearings under the fly wheel and the clutch/auto oiler?

 

[Wood Doctor]

Head gasket or crank seals

Considering all the other things that he has already done, I have to agree. Crank shaft oil seals could be leaking air, and it could be either side.

Replacing crank seals is not an easy fix, to say the least, and after only a few years of engine operation, that is not a typical failure. I also recommend opening up the high-speed setscrew on the carb to see if she starts to throttle down. That may require raising the idle up to prevent the engine from dying. This is indeed unusual to have such problems with a new or rebuilt carb, but give that a try first and see what happens.

 

[ShaneLogs]

Crank seals probably.

 

[watsonr]

Thank you for the help. I was hoping not to have to seperate the crankcase, but I may just have to if it is that Gasket. it looks new, but i'm running out of options. When you say crank seals, are you talking about the cover that goes over the ball bearings under the fly wheel and the clutch/auto oiler?

Crank seals don't require a case split. Remove the flywheel and the clutch and oil pump and they are right there. Did adjusting the low side needle do anything... as bring the RPM down when you richen it?

 

[ttyR2]

Pressure/vac test the engine before doing anything. If it passes, seals aren't needed.

I'd give the carb a thorough going over before I tore into the engine.

 

[00 steve]

Considering all the other things that he has already done, I have to agree. Crank shaft oil seals could be leaking air, and it could be either side.

Replacing crank seals is not an easy fix, to say the least, and after only a few years of engine operation, that is not a typical failure. I also recommend opening up the high-speed setscrew on the carb to see if she starts to throttle down. That may require raising the idle up to prevent the engine from dying. This is indeed unusual to have such problems with a new or rebuilt carb, but give that a try first and see what happens.

The 046 has not been made in 13 years. I would guess it has more than a few years on it.

 

[Nardoo]

Torn carb boot.

 

[GrungyDungy]

Eureka!

Head gasket or crank seals

Thanks for all the help. I finally got a chance to tear into it today, and I'll be damned if the crank seal behind the automatic oiler wasn't chewed up. ran out of time to fix it, but I'll post next week if I get a chance to toss it all together.

 

[stihl for life]

i would guess it would be crank seal but try a new spark plug .. if not try new gas mix it a little richer 40/1 or 32/1and see if that work. might be running lean or water in the gas . thanks brandon

 

[GrungyDungy]

Stihl No Luck

So, thank you guys for all the help, I've replaced the crankshaft oil seal with no change in performance. Spark plug is new and we run all our saws at 40:1. I'm now at a complete loss for what to do. The saw has been shelved for now and as much as I hate walking away from a project, I'm considering making it a parts saw. Any other ideas before I throw in the towel? And to 00 Steve, This is a valid point, but a couple seasons is my best guess. It is my second year on the crew, but the saw looks almost brand new. My guess is that they had issues with it and shelved it. I fixed all the rest of the saws and came back to this one because it was extremely difficult to diagnose.

 

[blsnelling]

Have you vac tested the saw? That's an absolute must in a case like this.

 

[cutforfun]

Do a vac/pressure test to be sure, I would ck the carb again, if the saw is running on choke than you are not getting enough fuel.

 

[GrungyDungy]

I've tested compression, it's good (around 140 psi). I don't have a vacuum tester, would it still be neccesary if the compressions good? The carb has already been replaced.

 

[watsonr]

I've tested compression, it's good (around 140 psi). I don't have a vacuum tester, would it still be neccesary if the compressions good? The carb has already been replaced.

YES... you could have a small crack in the fuel line, carb boot or something sucking air you can't see. Does richening the low do anything? Cylinder bolts tight?

 

[fearofpavement]

The compression check only checks the integrity of the piston/cylinder/rings. A vacuum/pressure check verifies that the rest of the system is leak free. On a chainsaw, the crankcase is a part of the fuel system (and sometimes the oiling system) and leaks can and will cause running problems. Places that can leak air and be problematic are the case to case mating gasket, the crank seals (you already addressed at least one side), the carburetor boot (if equipped), the impulse line (the line itself or where it attaches on either end), the carb itself, and probably some things I forgot.

From how you described the saw's running, it appears to be too lean. This can be caused by the saw not getting adequate fuel or by it getting too much air.

One thing to try to verify that it is a lean issue is to start it and before it dies, try dribbling some mix gas directly into the carb and see if you can keep it going. If you can, then it for sure is not enough fuel or too much air.

May have to hoe some ground you already covered. ie, maybe the new carb is defective, etc.

One thing I like to do is change components to see if I can "move" a problem from one saw to another. ie, switch carbs with a good running 046 and see if they both run the same or not.

Keep plugging away at it, there has to be a reason...

 

[jockeydeuce]

Cylinder bolts tight?

One of the first things I look at lately!....I have had a ton of Stihls come in here lately with loose cylinder bolts and or blown base gaskets if they still had the paper gaskets.

I've sure seen a lot of "Help" threads lately, where numerous people have said vac test the saw, and nobody does. They just keep trying different things, hoping for a better result.....Vac and pressure testing is the only sensible and efficient way of trouble shooting PERIOD!!

When I first started playing with saws, I didn't have the tools to vac test, but I would take a saw to my dealer with the carb and muffler pulled an they would do it for me for under $20.....That's cheap to narrow everything down to the carb and fuel supply!!

 

[Wood Doctor]

Hours of Opeartoin

The 046 has not been made in 13 years. I would guess it has more than a few years on it.

Yes, most were made about 15 years ago, including the one I worked on last week. However, you have no way of knowing how many hours of operation are on the saw, even if you know when it was first sold.

Hours of operation, how the saw was used, and how the owner treated the saw --> That's what's important.