Baldy

I'm trying to get my weed whacker going. It's a Stihl FS76, 2 cycle motor, nothing unusual. It just won't start. While I was at work a friend somehow got it started, but he couldn't get it to stay running long.



It's getting air, and I cleaned the filter. The compression sounds great. There is no spark arrester screen, and I took apart the muffler to look for mud dobber nests, and it's all clear. I took apart the spark device (whatever it's called) and wire brushed the flywheel, it has surface rust on it, and the spark plug has got what looks like a good strong spark.



The fuel tank has been flushed and filled with new gas/2cyl mixture. I replaced the primer bulb (old one was cracked and broken). I found the factory specs online for the carb jets, adjusted it to that, and it still wouldn't go. I took apart the carb and soaked it in gas and put it back together. The diaphragm doesn't looked dried out, but it has a teeny tiny tear/crack in it, maybe 2mm x .5mm, at the edge of the diaphragm. The fuel hoses are fine, and the priming and choke work as they should.



I removed the air filter and sprayed starter fluid in there, and it would crank up for about a second then die. Is that tiny crack/tear keeping it from running? What else can I do?

phinsup

Ethanol prolly ate up the fuel pump.

1988RedT2

Try a new diaphragm for the fuel pump. It's a Stihl, you can get parts.

Baldy

Ok, bought the rebuild kit. The kit came with a bunch of extra parts, it's intended for several different models. I Replaced the top gasket/diaphragm (2 pieces, one thick, one thin/flexible), the bottom gasket/diaphragm (though the only diaphragm that fit was thin plastic film, not rubber), and the spring-loaded pivot thing and the jet-looking thing it moves up and down.



I primed it and easily got it started on choke, and it ran for a few seconds before shutting off. Got it started on choke a second time, ran about a minute, and died. I couldn't get it started again, on or off choke. Not sure what to do now, starting to **** me off.

1988RedT2

Plug look wet or dry? Twiddle with the carb screws, like a half turn from where they are now.

phinsup

take the carb off, take it apart soak it in carb cleaner, swear at it and call it a piece of ****, shake your fist at the dog, apologize to the dog, shake your fist at the wife, quickly apologize have some make up nookie, go get some dynamite, make a big crater where your weed whacker used to be, steal the neighbors weed whacker, have a beer.

Baldy

Ok, did all that up to the dynamite part. Looking for dynamite now.





I waited awhile, then tried it again. There is a H and L screw, and an idle stop screw. Following some adjustment instructions I found, I backed the L screw out 1/4 turn from factory setting. Choked, cranked, no start; open choke, started, ran for a couple seconds, then died.



Any time I applied the throttle, it would die immediately.



I hate fuel tuning, because I suck at it. With 2 adjustment screws, I have no idea what combo to go for, I can just try over and over I suppose.



As for the spark plug, yesterday when I removed it, it looked fine and sparked really well (after I cleaned up the wheel thing that triggers spark). I haven't removed it again yet, but I wouldn't know what to do if I found it wet.

1988RedT2

The H screw affects the part/full throttle mixture. The L screw affects the idle mixture.



If the plug is very wet, you've got too much fuel, dry and it's not enough.



Sounds like you should back the H screw out a bunch. Unless your plug is wet, of course. Have you had a beer yet?

j9fd3s

i'd start with both screws at the factory spots. adjust the L screw until it idles, and then adjust the H screw until it runs.



screwing it IN should make it leaner.



if you spray fuel in and it runs, it sounds lean? i'd go half turns on the screws.



i don't know anything about um anything

Baldy

I got it to idle on its own, but it would die on decel, and on full throttle, and other random times. And the plug was super wet at this setting.



Called brother, who has training in small engines (golf course school, or something like that). He said he's encountered the exact same issue, and it was a small hole in the fuel line letting in air.



Sure enough, fuel lines are dry rotted and probably had holes in them before I started tugging on them. Gonna get some new line, dry off the spark plug, and try again from factory setting.