I'm having problems with my 20581 toro, its a 1987
home owner rear bagger. When it runs at higher rpms
it has a intermittet knock. Cleaned the air cleaner,
carb,new sparkplug,cleaned the exh port. Is it the gas
Run MMO or Techron through it, and bump the octane. If it still knocks run the next thicker grade of oil. If it still knocks pull the head. Those things are relatively simple. If it's not the the big rod end my guess would be built up carbon in the CC.
Wade a minnit. Is this a 4 stroke or a 2 stroke? 'Zuki powered Toros came with either.I scored a pair of Toro freebies. One of them was the 'Zuki 2 stroke. It was a fine mower until I boogered it up. In '09 ,when I was on chemo, I needed a project for the time off. I picked up another old Suzuki,Toro GTS. this one a 4 stroke.It starts on the first pull about 75% and 95% by the 2nd. If if it doesnt start on the 3rd, I forgot to open the shutoff.Not too shabby for a free mower with 20 yrs of service on it mowing a 1/2 acre lot.
Other things to check for tightness. Could be the engine to deck bolts, or the blade/ brake stuff. I'had puttered along keeping old freebies with a flathead B+S or a Tecumseh. engine. The Suzuki 2 stroke was too complicated for a small engine. The 4 stroke has been very good to me. I use it for places where the sit down is too cumbersome. It mows great and runs better the longer I run it. I mix an oily 32:1, 87 E 10 uni-mix and add a cap of MMO to every OPE tank. With a mower that runs well, why fix it? I change the oil every so often with what ever 10W30 I have handy. I clean the sponge air filter and give it the merest drop of oil.I feel no compulsion to even look at the plug. Learned that lesson from cars. Less is often better than more. My best freebie so far. All it needed was a shoulder bolt. I harvested one from an earlier Toro