stihl 028 super leaning out

[kkemp]

My 028 super is running lean at wot . It'll sound good for about 3 seconds then go lean . It has a new fuel line and has passed a couple pressure vacuum tests . Could that be carb related or seals that leak when it gets up to temp .

 

[redoakneck]

Tank vent??

Possible seal, but it passed the test,

Choke flapper getting too close??

 

[kkemp]

Pretty sure it's not the choke it seems to be working good I took the filter off and ran it for a couple seconds still acted same . Forgot about checking the tank vent .

 

[redoakneck]

Pull muffler and look for scoring.

Hopefully still in good shape.

Great old saws, did you try to clean the carb??

 

[kkemp]

It had a new piston put in a couple months ago . Looked at it a couple days ago . Looks like new . I put a carb kit in it .

 

[Basher]

Fuel shortage, carb and or impulse related. Racing at idle most often tells of an air leak.

 

[redoakneck]

Did you figure out what happened to the old piston??

Make sure cylinder bolts still tight

 

[kkemp]

Cylinder bolts are tight . I bought the saw with a bad piston looked like it was run lean. But it has ran great since . Responded well when I turned the needles on the carb. I had posted a thread over on AS and they came to the same conclusion that is was too lean..

 

[Nitehawk55]

Tank vent on those got some dirt in them and would cause them to lean , check that for sure .
New line and reinstall the grub screw .

 

[paragonbuilder]

My 394 did that. Replaced the seals, and it's all set now.

 

[MustangMike]

I presume since you changed the line the fuel filter is new? Also, try changing the plug.

044#1, likely my favorite saw, behaved very poorly at the last GTG I attended. Hard to start, and seemed to be running lean, and was not strong. Changed plug, fuel filter & Air filter and all seems good! Sometimes, we over look the obvious ... thinking it is something worse. Always do the simple stuff first.

 

[Gunn]

One of my 064s did something similar. In my case, the fuel filter was causing it to starve for fuel. Replaced the orange AM one with a new black and white OEM one and it was good to go.

 

[kkemp]

I presume since you changed the line the fuel filter is new? Also, try changing the plug.

044#1, likely my favorite saw, behaved very poorly at the last GTG I attended. Hard to start, and seemed to be running lean, and was not strong. Changed plug, fuel filter & Air filter and all seems good! Sometimes, we over look the obvious ... thinking it is something worse. Always do the simple stuff first.

It has a new fuel filter and air filter . Put a new tank vent on tonight and checked all the screws . Took about 5 min of cutting and it started doing it again .

 

[Canadian farm boy]

It has a new fuel filter and air filter . Put a new tank vent on tonight and checked all the screws . Took about 5 min of cutting and it started doing it again .

Sounds like an air leak to me. Probably a small leak that only happens when the saw gets hot.

 

[kkemp]

What would be the first thing to check if it's happening when it's hot ?

 

[paragonbuilder]

What would be the first thing to check if it's happening when it's hot ?

I vote seals.

 

[Canadian farm boy]

I vote seals.

Yup. Agreed. Personally for the price of new crank seals I would just change them.

 

[Duane(Pa)]

Try running it in a bucking cut (or just piss rev it) with no vent at all before you get wrapped up in an air leak...

 

[Duane(Pa)]

Did you put a kit in carb? Has the saw been run on e fuel? May have an old/weak diaphragm that is unable to keep up.

 

[Nitehawk55]

If not the vent check the impulse hose , manifold (cracks) as well as the carb diaphragms and screen are'nt dried out or plugged with sawdust .
Beyond those I would be suspect of a seal / leak causing it to lean out .