Broken mower blues
May 27, 2010 9:15 PM   Subscribe

Why is my lawnmower engine suddenly racing? Can I fix it myself?

I was using the mower on some fairly tall weeds. There were sapling stumps in there and I may have bumped one. Anyway, the thing started racing like mad. Shutting it down and restarting didn't fix it, nor did letting it sit for a couple of days. I don't want it to throw a blade through my foot so I'm letting it sit some more (I have a backup).

Is there a governor in there somewhere I popped a spring off or bent? Did I mess the carb up? I took it apart as much as I felt comfortable with (it's a pretty new mower and I'd rather not get into a repair I can't handle and ruin it) and couldn't see any obvious problems. I did pull and clean the air filter; didn't help.

Is there something easy I'm missing, or should I just take it to someone who knows how to fix it? It's a Toro "Recycler" self-propelled mower with a 190cc B&S engine.
posted by Camofrog to Home & Garden (9 answers total)
Some engines have a sliding throttle on the physical engine (instead of up on the handle areas). It sounds like you could have bumped it with the stumps and moved it to a higher speed.
posted by msbutah at 9:26 PM on May 27, 2010

I've had the same thing happen to me. It's a really dumb design. If you take off the air filter you will see a spring contraction. make sure the spring hasn't come off and is pulled tight. I never got mine to work correctly again, but you might be able to order that part and replace it.
posted by meta87 at 9:26 PM on May 27, 2010

I had the same problem and it was a spring that was bent and off. Can you see the springs when you pull off the air filter?
posted by mattbucher at 9:29 PM on May 27, 2010

Does it still mow? My first reaction would be that you broke the key that transmits torque to the blade assembly. The engine would then be spinning like mad with no load on it, because the blades are not actually rotating.
posted by defcom1 at 11:24 PM on May 27, 2010

Jesus. An engine that's "gasping for air" will not turn faster, it will turn slower. That's what the throttle is.

If the blade isn't loose, then it is the governor. As others mentioned, this is a throttle that's spring loaded and reacts against the load on the mower. The ones I've seen use air pressure from the cooling fan thing (the circular grate that spins)- when the engine is at full (or "rabbit" speed), the wind pressure pushes on a sail kind of thing that keeps the throttle partly closed. When you get to some tall grass, the wind slows down and allows the throttle to open more and speed up the engine. Same thing you do with your foot when you are driving up a hill... "hey, the car is going slower, better give it more gas".

Fix that.
posted by gjc at 5:15 AM on May 28, 2010

I'm also going to guess your blade is no longer being driven by the engine. That seems more likely to break in an impact than the governor.
posted by pjaust at 5:35 AM on May 28, 2010

As I said I cleaned the air filter; it's not that.

I figured out what's going on, but I'm not sure how to fix it. There's a governor that is letting it rev way up, with a spring mechanism and pushrod to control it. It doesn't look damaged though; if anything, banging it against a stump should have slowed the RPMs down. The business end is buried under the gas tank so I'll see if I can pull that off after work and see what's going on.
posted by Camofrog at 5:39 AM on May 28, 2010

Thanks gjc; I'm sure it's something like that. I posed my above comment before seeing yours. I'll see if I can find the "sail" and all those bits.
posted by Camofrog at 5:41 AM on May 28, 2010

I took it apart enough to see the governor linkage, which looks adjustable, but I'd need to have the engine running in order to adjust it which is not something I can do by myself easily or safely with parts hanging off it. (gjc: this mower does not have that "sail" you talked about...) So I "fixed" it by rotating the plate the spring is attached to on the other end. It's not really supposed to rotate, so it's not really fixed properly, but it runs at a non-terrifying RPM now and is working fine. As a bonus, it's all back together with no leftovers. I still have no clue why it got out of whack, since nothing looked bent or stretched or otherwise out of place, but whatever.

As is often the case here, I didn't get the exact answer, but I got enough guidance and inspiration to get the problem solved. Thanks again!
posted by Camofrog at 2:36 PM on May 28, 2010

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