Bought a new 163cc Toro personal pace rear-propelled mower in 2016 and it has performed admirably until the last year or so. Very little "umph" going uphill and so-so going downhill. Have replaced the drive belt (twice) and the traction cable (this year, and adjust it often). Question: does the ability to self propel decrease over time? Time to get a new mower?


  • Welcome to Motor Vehicle Maintenance & Repair! Have you ever changed the oil in it? Also, more than likely the issue is a fueling issue and the carb needs to get cleaned. Jun 21, 2022 at 16:07
  • If the throttle is self actuating (my B&S mower has no user control) that might need cleaning up, as mine does from time to time. I also replaced the rubber priming bulb this year: it was perishing and the air leak affected the carburation. Jun 21, 2022 at 17:43

1 Answer 1


I suspect as Paulster2 pointed out that you have stale fuel in the carburetor.

The problem with regular gasoline is that it doesn't stay fresh for long. If you use your engine every 2 months or so and the engine is fuel injected, this is not an issue. Gasoline gums up slightly in 2 months but if the engine is fuel injected, the control system probably figures this out and adjusts the injector timing accordingly.

Carburetors are different. If the fuel gums up, it will restrict the flow of fuel into the engine. In the worst case, the restriction will be permanent. This happens especially with devices that are used only rarely (emergency backup generator) or only seasonally (lawn mowers).

One solution to this issue is to drain all fuel the last thing in the season. You can use a hand siphon to make the tank empty, and then use the mower until the engine cuts due to fuel starvation. Then some carburetors have a drain screw which will allow to drain whatever fuel is remaining in the carburetor, if any. If you use the drain screw, remember to tighten it so that your fuel doesn't fall out of the carburetor the next time you fuel the mower! And remember to do this before winter, if you do it in the spring the first time when using the mower, it won't help anymore and you may need to get the carburetor cleaned.

Another solution is to use fuel stabilizer. I don't know how well they work for such a long storage time as over the winter.

A third solution is to see if you can find "small engine gasoline" / "alkylate gasoline" in your area. It's significantly more expensive than regular gasoline, in areas where taxation is low it's probably 40% more expensive in the pump (if you're lucky enough to find it from a gas pump) or even 100-200% more expensive if you need to buy it in small plastic containers. The benefits of small engine gasoline are many: the exhaust doesn't smell as much and is less harmful for your health, it burns cleaner so less carbon deposits in the engine, and it stays usable for 3-5 years without adding any additional stabilizer. It also doesn't contain any ethanol with the issues ethanol mixtures bring.

There are two ways to use small engine gasoline. One is to use it always in carburetor fueled devices. Another is to use it for the last tank before winter. If you use it for the last tank (or last N tanks) before winter, you need to ensure the tank is practically empty before adding the small engine gasoline. I suspect that even 25% regular + 75% small engine gasoline mixture might gum up, but 1% regular + 99% small engine gasoline mixture probably doesn't. One possibility to avoid this regular + small engine gasoline mixture is to use small engine gasoline for the 2-3 last tanks during summer before storing the mower for the winter. If you have 20% regular + 80% small engine gasoline for the third last tank, and then 20% (20% regular + 80% small engine gasoline) + 80% small engine gasoline for the second last tank, and 20% (20% (20% regular + 80% small engine gasoline) + 80% small engine gasoline) + 80% small engine gasoline for the final tank, then that's only 0.8% regular in the last tank.

My approach is that I always use small engine gasoline in carburetor engines. Never any other type. I'm lucky that small engine gasoline is sold from a pump in my area, so I don't have to pay huge costs for the plastic containers.

Another issue might be that you have avoided the oil change for too long. While you're at it, change the oil and don't use some 10 year old old container but rather fresh motor oil as even unopened motor oil goes stale.

If it's not fuel or oil, then it could also be the spark plug. Pull that out and take a hard look at it. In fact, you probably will want to look at the plug before having the carburetor cleaned since looking at the plug is easy, but cleaning a carburetor isn't.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .