Tractor races, produces less power
Hi everyone -
I believe this is a question of general small engine mechanics, but here are the particulars of my machine, in case it's helpful. It's an older Craftsman tractor, with a Briggs engine, model 28N707, type & trim 0160-01, code 9406094B.
In response to the amount of oil it was burning, I pulled the engine and fearlessly replaced piston rings. Being mechanically inclined, but also a bit of a moron, I figured this would be doable; and it was, ultimately. After pulling the engine three times, I had it put back together (with no parts left over, even!), the valve timing correct, and, finally, valve clearances set correctly. And it runs! Mostly!
And now, The Problem: it revs much higher than it used to, even at low throttle settings. It drives fine (though faster - which is plenty fun), but with the blades engaged, the engine rpm drops very noticeably.
Intuitively, I believe the carb needs adjustment, because it runs a bit rough. But, again, moron. I seated the adjustment screw, backed out 1.5 turns, and with the engine running, adjusted until I found the spot where it ran smoothest.
Other information: at one point, with the throttle at its lowest setting, the engine rpm started rising on its own; it stayed high until I reached in and closed the throttle at the linkage - it was ok from there on. I should also mention that the idle speed adjustment is set such that the throttle is able to close down correctly, so I believe I have that set correctly.
So. Any guesses what I screwed up? The rising rpm thing makes me wonder if I messed up something with the governor (boy, do I hope that's not true), but the high idle, rough-ish running, and drop in power elude me. Should I just go back out and play around with the carb adjustment some more? Or should I be looking elsewhere?