have you pulled off the black plastic cover between the blade and the mowing deck? one of the weak spots on the bbc models is the cover cracks or a ton of debris collects within the cover causing the belt to slip. in that case the blade will slip under load but shouldnt cause the engine to run poor. if the belt is slipping when you enguage the blade it will seem to take forever for the blade to get to full speed. also check the brake plate pad on the assembly as well it could be worn but thats usually when you hear a scraping noise when you disengage the blade. The last part to check is the idler pulley that goes again the bbc belt, those pulleys may seize sometimes. even those are good mowers i feel the bbc on the toro mowers are more trouble then their worth.

"I have a 1990 Toro GTS 5 with the suzuki 5hp, bbc, 3sp rear bagger - GREAT mower! I use it to mow my 1/3 acre yard and have done my best to preserve it because I like it and how it cuts so much. On top of that, so many of the new mowers just seem cheaply built for the money - my toro is SOLID!"

RB> There are well made expensive mowers sold now as there were when you bought the Toro.

"Anyway, it's been running and cutting great with the bag on, but I put the mulching attachment on the other night (after not using it for about 2 years) and started having some problems. In moderately heavy grass, the mower bogged down significantly and as it did, started knocking - severely."

RB> It's generally not a good idea to mulch heavy grass, especially if it is at all damp. Take small cuts until you get the grass down and then do mulching cuts frequently. Many perfectly good mowers will choke up if you try to mulch too much a time. You might look for a buildup of cut grass under the deck.

"It knocks every time it boggs down and knocks louder and louder the more it boggs. The grass was heavy, but not heavy enough to clump up or even notice any clippings. Mower has always been well maintained and blade is sharp - it's a high lift blade, oil is full. I'm forced to mulch lately in an attempt do everything I can to improve soil conditions. "

RB> Although it is possible that the motor is suddenly giving out I doubt it. A knocking or banging sound is common when too much grass is built up under the deck. So check that out first. If that doesn't do anything, I would ask your local mower shop to take a look at the BBC mechanism and evaluate the engine.

RB> I have to assume the motor is wearing out - being that under load, it's severely underpowered."

RB> There are several other possibilities, so eliminate them before buying into the less likely choice of a worn out motor.

"I have a backup motor, but it is just as old, so I can't rely on it for much longer either. Should I consider replacing the mower? "

RB> Not yet.

"I've been looking around on the internet and narrowed it down to two mowers I would consider. The JD JX75 and the Honda commercial HRC216HXA."

RB> Unless you are running a lawn mower business why do you want a commercial grade mower. Seems like gross overkill for a 1/3 acre lot.

"I want a bbc, set speed trans (no personal pace), and a honda, suzuki, or kawasaki engine (no briggs for me - no disrespect, just have seen too many that don't last and/or burn oil)."

RB> There's not an engine made by a major manufacturer that won't last 30 years IF it and the rest of the mower is maintained properly. It is just as easy to abuse and burn out a Kawasaki engine as it is a Tecumseh.

"Would prefer to pick up a nice used one but may buy a new one, IF you agree that I need to buy a new one! Would you tell me to look at any other mowers? Toro Pro-line's look good too, but not quite as user friendly as the JD or Honda. Should I just rebuild the motor in my current Toro? Help! "

RB> Unless you have a burning desire to buy new equipment why not try to fix what you have. It's only 15 years old.