stihl 028 bogs down under load

[Polio66]

I replaced the piston and cylinder head in a 028 AV wood boss with a used 44 mm piston from 028 wood boss. The saw starts, idles well, runs at high rpm without load, BUT loses power (bogs down?) then stalls under load (about half way through a 12" log).

Here is what I checked:
*tank vent is not plugged
*carburetor rebuilt: new diaphragms, new needle valve, ports cleaned with compressed air
*cylinder head screws are tight
*fuel filter not plugged up
*intake manifold screwed tightly to cylinder head, no visible cracks in manifold
*fuel line though cracked on outside seems to hold pressure

I noticed the inside of the muffler was oily, and I thought I may be running rich. I screwed the H screw leaner (clockwise) (just less then 1 turn out from closed). The saw bogged down under load, just the same.

Thought maybe the pulse tube (manifold to fuel pump) has a leak, but even if I did wouldn't the saw run lean, not rich???

Any ideas ?????

 

[thompson1600]

My first guess (assuming you have a sharp chain) would be the piston rings are leaking and need replacement.

Tom

 

[Lawn Masters]

the fuel line is cracked as you noticed, REPLACE IT. that will cause a lean condition later if you dont replace it now, and then retune the carb after that.

dont be half azzed and pay for it later, a few small bucks now for a fuel line, vs a whole piston AGAIN later, you tell me which you'd rather have.

 

[biga]

do a search on saw tuning and set the mixture screws the right way .. just because it turn the high rpm dosent mean its right .... top rpm isnt top power ... you want it to 4stroke at wot that will let it run rich enough to have good power and not burn a piston

 

[rmihalek]

By the way "wot" is wide open throttle.

 

[Fish]

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