Stihl 046 Magnum runs perfect then randomly dies

[user 122190]

I had a similar problem with my 460. I put in a new tune-up kit, and took all the electricals a part, wiped them all down, inspected it closely, saw nothing wrong and put it back together. It ran perfectly after all that. I think is was the fuel filter, but never put the old filter back to verify.​

 

[alexcagle]

I had a Husqvarna saw recently that had an almost new oem Partner style fuel filter on it. It was severely restricted. I put a short hose on it and tried to blow through it to test it, and could not. I found out later that my customer cleaned the filter with regular carb cleaner, which strangley seemed to fuse the filter strainer element like the solvent of a pvc glue.

 

[Wood Doctor]

Yep, could be as simple as the pick-up body (fuel filter). Replace that first before you do anything.

 

[Timbco84]

I realize you said you pressure/vacuum tested it, but did you do it at the carb mount with a stihl block adapter so it includes the intake boot and impulse hose in the test? If not, it could be the boot opening up a crack. I've seen saws run fine because the vacuum held a split shut and ran fine until the seal got flexed apart.
An easy test for that is to idle the saw while on the ground, and push down and pull up on the handlebar, and make the tank to crankcase connections flex. If the idle changes a lot, or dies, that could be it. It is ok if it changes a bit because you are momentarily changing the pressure for a second.

I blocked it off behind the carb, thus including the intake boot. I pulled vacuum and pushed pressure through the impulse hose with the mity vac, thus including it also. Flexed the saw around while under vacuum and it held unfortunately. I actually went as far as taking the clutch off and spraying the crank seal (and everything else) with soapy water while under pressure just incase it was a super microscopic leak...no bubbles.

 

[Timbco84]

What size is the exhaust hole on your muffler? Is it pencil size or bigger than a dime? If it is the one with the pencil sized hole then open it up to about 16mm.
This is similar to a problem I thought was a carb issue on an 028 super, but it was the small muffler opening choking the saw up.

It's got the big hole, and dual port muffler cover. Checked the screens inside and they are clean and clear of soot/buildup. Thanks

 

[Timbco84]

I spent about 7 hours chasing a very similar gremlin on an MS660. Just got it sorted out yesterday and a different carb is what fixed it. It would tune nice, idle, cut, etc. Then it would just randomly bog down and flood out. I had the carb apart 3 times, put a kit in it, to no avail. What a pain...
Sometimes I could cut a dozen 12" oak cookies and it worked great then would fall on its face.

Your problem sounds all to similar to mine. Being that it is obvious that my saw spent a lot of it's early life sitting around in the garage...probably with fuel in it, I can see how something could be gummed up and causing a problem even though I rebuilt the carb with a oem stihl kit.

 

[Timbco84]

I had a Husqvarna saw recently that had an almost new oem Partner style fuel filter on it. It was severely restricted. I put a short hose on it and tried to blow through it to test it, and could not. I found out later that my customer cleaned the filter with regular carb cleaner, which strangley seemed to fuse the filter strainer element like the solvent of a pvc glue.

That's good info, I can rule that out though I think. When I pull the carb, the pressure in the tank pushes fuel out at me through the new filter and fuel line. have blown through it with the cap off and it has plenty of flow.

 

[Timbco84]

It's really looking like the Carb or the Coil could be the culprit, it comes down to a coin toss on which one to try first. Probably try the carb just for the sheer fact the the saw sat around unused and thus probably gummed up. That and the fact that the saw has extremely low hours so I would hope the coil would still be sound. Unless it was just lemoned from the factory.

 

[alexcagle]

One more simple test I do to fuel lines if I have a gremlin
Is; with some fuel in the tank; to take my compressed air nozzle and blow just over the top of the carb end of the fuel hose creating a short siphon effect spray, (to confirm unrestricted flow).
Make sure you are not spraying around an ignition source. -You want the siphon effect, not the "Gene Simmons" effect. Lol

 

[alexcagle]

I agree.
I've had carbs before that were simply unfixable.

 

[Chainsaw Jim]

I suppose it's time to check another carb. Did you spray the new carb kit off with carb cleaner when you installed it? Because if so the carb cleaner can crinkle a diaphragm up worse than ethanol fuel. I sprayed one off with b-12 once and it went stiff as soon as the cleaner evaporated.

 

[alexcagle]

I suppose it's time to check another carb. Did you spray the new carb kit off with carb cleaner when you installed it? Because if so the carb cleaner can crinkle a diaphragm up worse than ethanol fuel. I sprayed one off with b-12 once and it went stiff as soon as the cleaner evaporated.

Like Viagra, Lol....
A little off topic; but, I get these evil looking giant hornets from hell on my back porch in late summer. That b12 kills them instantly from 6 feet away. --nothing better...

 

[Shiftit1]

It's really looking like the Carb or the Coil could be the culprit, it comes down to a coin toss on which one to try first. Probably try the carb just for the sheer fact the the saw sat around unused and thus probably gummed up. That and the fact that the saw has extremely low hours so I would hope the coil would still be sound. Unless it was just lemoned from the factory.

Hi I know this is a pretty old post but figured I would give it a shot. I am having a very similar issues to yours.

. New top end, crank seals, fuel line, fuel filter, impulse line, vent seems to be working properly. Rebuilt the carb with walbro kit and still the same issue. All parts are OEM. Mine has the old style HD16 carb, not the HD16C. I also did vac and pressure tests that seem to hold indefinitely. Tested tank, fuel line and carb also.

It will seem like it tuned ok then all of a sudden it acts up again. Sometimes I can hear it happening and catch it but not always. Almost sounds like its running out of fuel, but I will richen it up well past where it should be and still does it.

I was hoping to find out if you fixed yours and what it was. Any help would be greatly appreciated. Thank you in advance!

 

[Wood Doctor]

Take a look at Post #23.

 

[Shiftit1]

Take a look at Post #23.

Thanks for responding. I realized I didn't say that in my list, but I did install a new filter with the new fuel line. I actually even tried puting the old one back in just to try it.

 

[alexcagle]

Check cylinder screws for tightness.
Impulse hose maybe not hooked up.
Rare, but possible: impulse hose misaligned or folded under at the carb connection.
Also; small bubble pools of water in the fuel tank are not uncommon in chainsaws. On the bottom, right where the fuel pickup is. Gravity

 

[stihltech]

So many ideas here, have not read them sll so I may be a rerun.
High speed nozzle/jet get sticky with age. If it does not seal, it will be very lean at idle and may stall. You may be able to order it. Will have to check as I am off work for a bit.

 

[lone wolf]

Carb.

That is my first thought when reading the description.

 

[Shiftit1]

Check cylinder screws for tightness.
Impulse hose maybe not hooked up.
Rare, but possible: impulse hose misaligned or folded under at the carb connection.
Also; small bubble pools of water in the fuel tank are not uncommon in chainsaws. On the bottom, right where the fuel pickup is. Gravity

I will double check the cylinder screws for sure. I would've hoped if theu were leaking it would've shown up on one of the three times I've pressure and vac tested it. But anything is possible. Impulse hose definitely connected,been apart a few times but im usually pretty good about double checking those things, but its definitely connected. I've also dumped the gas on this saw several times to take it apart. Easier than have it leaking . Have filled it with both my premix and the vp gallon cans.

I keep feeling like I've covered my bases, only other things I can think of would be carb or coil.

Its just crazy sometimes it runs good for a little while and other times a few seconds. But the times I don't catch it from stalling it usually starts right back up.

I will definitely check those bolts though. Thanks for you input!

 

[Shiftit1]

So many ideas here, have not read them sll so I may be a rerun.
High speed nozzle/jet get sticky with age. If it does not seal, it will be very lean at idle and may stall. You may be able to order it. Will have to check as I am off work for a bit.

So many ideas here, have not read them sll so I may be a rerun.
High speed nozzle/jet get sticky with age. If it does not seal, it will be very lean at idle and may stall. You may be able to order it. Will have to check as I am off work for a bit.

Looks like there is a part number for it If I am looking at the correct part. I don't know if its available though. I would have to call my dealer. Im not q
100% yet but considering just ordering a carb. Just holding off because of how intermittent the problem, it runs really well aside from this issue.