Stihl backpack blower not starting...

Richard · May 25, 2009

I've got a Stihl backpack blower, the 2 stroke variety.

On starting, I always choke it & pull once/twice until it sputters and then turn choke off and it usually (99.999999999% of the time) lights off.

Used it last weekend and did my usual routine. One thing different though... I was worn out from all the outside activity and forgot it out there. Storm was moving in so I simply moved it under the covered patio area (full roof). Things don't get rained on there but I'm sure they might get damp/wet from rain overspray.

Last Saturday, one week later I pull it out (of garage, I had already taken it back to garage a day after storms)

Bottom line...it will NOT start.

Symptoms:
Spark plug: Pulled out, it's sparking, swapped with another working one, nothing
Air filter: Looks clean, had a bit of stuff in it but I've tried to start with air filter on AND with air filter off so I know it's not a clogged air filter
Fuel filter: Pulled out for visual inspection, tank looks clean to the degree I can see inside there, nothing visible on fuel filter clogging it

Process: I've pulled & pulled starter and nothing happend. I pulled plug out and some vapors came out of plug suggesting to me the fuel is indeed getting into chamber and atomizing. I return plug & pull...I get a faint ignition sound as it sounds like the piston fired once or maybe twice...then nothing. I pull again...nothing. I get nothing until I remove spark plug and put it back in. Almost as though I'm allowing fresh air inside BUT, my air filter has been on AND off so I can't think it's any obstruction.

This partial sparking symptom is the same with either spark plug installed. The plug has come out wet so I initially thought I flooded the engine. After it sparked & sputtered the first several times (after I took plug out EACH time) I figured any flooding was over and it would start. Nada. I might add I also pulled the cord with the plug out to help air out any fuel that might indeed be in there.

The top of the piston head, which you can only see a bit of through the spark plug hole, appears to be damp which is why I thought it flooded.

I've not taken anything apart deeper than the air filter & spark plug. I'm planning on dumping the gas out BUT, I'm using the same gas that I've been using and was working fine just last week. Same can, same batch of mix.

I'll admit I'm somewhat baffled... I seem to be getting fuel, ignition and compression.

Any thoughts? Oh... I've wondered about an obstruction in the exhaust pipe... perhaps a dauber or something got in there and created a mud nest while it was under the roof??? If so, would that KILL the engine or as I'd suspect, just make it run poorly??

I'm heading out shortly to fight this fight some more!

AchingBack · May 25, 2009

It sounds like you are getting fuel, maybe just not enough. Look inside the tank. Is there a fuel line with a fuel filter attached? Check to see if the line is kaput, or if the fuel filter is dirty, or detached. Another test is to see if it will start with a quick shot of starting fluid into the air cleaner. If it does, you definitely have a fuel delivery problem.

wushaw · May 25, 2009

How old is the blower, if several years you may have a bad fuel diaphram, if ya ever dealt with carburetors some (motorcraft for ex) had a diaphram for an accel pump that would crack over time.
I had to replace one on my Sthil pole saw this last winter.

J_J · May 25, 2009

Richard, do this. There is probably a spark arrestor screen in the exhaust, pull it out, and throw it away or get a new one. I have run Sthil backpacks since 1988. That BR-400 is a good blower. 300 or 400 series, all good.

charlz · May 25, 2009

I have a handheld Stihl blower. Starts just fine if you follow the starting procedure. But if my wife or someone has flooded it is a huge pain to start. I find pulling the plug and then pulling the starter some number of times helps. Usually you can see gas spatters on the concrete if it has been flooded. Clean it all out and then follow the starting procedure. Doesn't seem to take much for it to be 'flooded'.

BigE_ · May 25, 2009

If indeed it is getting flooded, then you can pull the plug and heat up the tip (spark end) with a propane torch until it is glowing red. This will burn off the carbon deposits, etc. You may just need a new plug.

Richard · May 25, 2009

Ok, so now I'm back and sweating like a pig. I love this 4,000% humidity! I just wish it would storm & get it over with!

I've pulled the carb assembly off, nothing clogging the airway to the cylinder. I then disassembled the carb, didn't notice any blatant dirt inside of it although it's possible a speck is inside one of the orifices.

Blew the line clean from carb to tank and no obstructions. Even blew on the fuel inlet onto the carb assembly. It didn't seem to work until I pushed down on what I think is the stopper (under what appears to be a rubber diaphragm).

I don't have any ether so I can't try that method quite yet. I DID however, try to squirt some fuel directly into the throat of the carb, that didn't get me anything.

Regarding the diaphragm, is that the black rubber part I found inside the carb? It was intact however I suppose it's possible it had a tiny leak? It certainly did not appear to be worn in any visual way.

When I took the supply tube from tank, off the carb, fuel was just gï½µshing out (to the degree fuel can gush out of a 1/8 tube).

JJ, the spark arrestor screen was removed soon after I bought this so I have a straight pipe out the back!

Here's something strange I noticed. I was pulling starter while also using my right hand to hold the unit still (it's up on the floor of my backhoe so I didn't have to bend over all day). While holding it, I thought to put my hand over the exhaust to see if I could even feel any exhaust coming out even the engine wasn't starting.

If the exhaust SHOULD in fact have air puttering out of it during the pull process, then I didn't notice any. I DID however, notice some air that was blowing to my hand, coming from what seemed to be between the cylinder and the exhaust. Everything is tight so it's not escaping from the cylinder at the exhaust manifold. It might be as simple as the fan moving air and this is to cool the fins. In fact, now that I think about that, this is very possible. I just found it interesting that even though the engine coasted over 10/20 times with a few sputters in there, I didn't notice any air from the exhaust tip.

Oh, and I dumped the old fuel out also however, I don't have any fresh fuel so if my can is bad I simply added more of the same bad stuff in.

Charlz, this thing has ALWAYS been very easy to start, especially once I get a few coughs/sputters out of it. One or two more pulls and it's off to the races. I have had NUMEROUS sputters out of it but still nothing.

It's like the darn thing is possessed and doesn't like me anymore!!

Wildbill34 · May 25, 2009

Richard,

On several occassions I have has the same problems with various pieces of equipment. 9 out of 10 times if I go get fresh gas and remove the old, it starts. My buddy next door is always laughing at me as I cuss, scream and holler trting to start something for the first time or second time of the year. He comes over and says, Fresh gas?????

I say no, then after he leaves I run to station and get some and the darn thing starts right up......

Coyote machine · May 25, 2009

Try a new plug gapped to correct spec and some fresh gas. Why mess with all the other things when those are the two likeliest things hanging you up?
I do not know if there is an electronic ignition on your blower like Stihl uses on their chainsaws, but if I had to guess I would say yes. Even though you think you are getting ignition, (from spark you mentioned), if the blower has an electronic ignition and it has crapped out you will need to replace it.