Lawn Mower Problem

[kamikazi_tom]

Half way through mowing my lawn my lawn mower started goin bananas. By bananas I mean the engine would ramp up speed VERRY fast, to the point that the lawn mower was almsot shaking out of my hands. Then after that it would die. My lawn mower is a push mower. I am assuming that this could be the cuprit of a dirty air filter. The high RPM's are due to the machine getting straight gas and no air? I am no genius on how motors work but I have a good idea. You guys think I'm right?
Thanks,
Tom =]

[catacon]

I'm pretty sure if the engine was getting just gas, it wouldn't run at all. Gas alone won't burn, it is the gas+air mixture that burns. Make sure the throttle isn't getting stuck and you can check the air filter (it should be on the side in a black box or something).

[hitchface]

Straight gas an no air wouldn't make too much sense. A leaner mixture tends to increase RPMs because the combustion gets hotter with more air. Of course, too much air and you won't get combustion, but the surge kinda rules that out.

Check the carb and intake gaskets. If they are cracked, they could be causing surges. Blow out the carb with compressed air, check the fuel filter for obstructions. Do those and I bet you'll find the problem.

[kamikazi_tom]

Thanks for the help guys =]

[glc]

There's supposed to be a governor on a lawnmower engine to keep it running at a steady speed. It opens and closes the throttle.

[Brad the best]

Originally Posted by glc There's supposed to be a governor on a lawnmower engine to keep it running at a steady speed. It opens and closes the throttle.

sounds to me like you have a governor problem , what engine is it ? honda ? brigss ? what color is the engine and what hp rating does it have . most have a internal centrifugal inertia governor , some times the weights will pop out to far and cause it to rev like crazy (mostly in honda's)

if you take the air filter off and look into the carb there should be a plate (throttle plate) is it sticking pretty much straight up ? shouldn't be .

you may have to adjust the governor , springs could of gotten stretched or linkage could be messed up . the briggs usually use a small piece of plastic on the outside of the flywheel that gets air blown at it and then pulls a piece of linkage and governs the engine , they break on occasion .

running rpm should be 2300 , you can buy a small digital rpm gage that senses vibration on the cylinder and tells you vibration they are about 13$ ( only works with single cylinder engines, which you have)

done anything to it lately? anything random happen ?

i used to work in small engines but got bored of them and moved on to heavy duty so if you tell me a little more i can hopefully help you out .

i would just start with a good general service and check the governor .

[Brad the best]

dirty air filter the mower will just choke out , black smoke and die . wont rev higher .

[kamikazi_tom]

Geez Brad you reallly know your lawn mowers

Anywho, I'll have my dad take a look at the stuff you recomended. It feels good to prove my dad wrong, but don't worry I gave all the credit to PC Mech!

Thanks fellas =]

[Petef56]

As I read through this thread, and before I hit post #5 I was thinking the problem
is with the governer. Specifically I think the governer spring broke. So I basically
agree with GLC and Brad.

---pete---

[hitchface]

Yeah it could be that. Remember my experience is with airplane engines. Little different.

[Brad the best]

Originally Posted by hitchface Yeah it could be that. Remember my experience is with airplane engines. Little different.

same basic principal

just way more simple , lawn mowers that is .

[hitchface]

Well, yeah, but you won't be finding any governors on airplane motors. Over speeding a prop is pretty easy because of that.

[Brad the best]

no but you probably kick butt at tuning carbs . most air planes i see have like 8

[hitchface]

My knowledge is more theory. I mean, plane engines are nice n simple for the most part (I'm not talkin' heavy jets) but I'm no mechanic. I learn all I know from our school's mechanic, who teaches all of the aircraft systems classes and does the maintenance on all of the aircraft. And let me tell you this guy is a whiz! He has a home built machine that is pretty darn awesome, does all of his own work to it.

On a more related note, how is it coming with that lawnmower motor?

[BigRed CC Dually]

Hitch,

Jets are simpler than recips. It's simply suck, squeeze, bang and blow for a jet, with a lot less moving parts (not counting individual blades of course)

[hitchface]

The process is indeed simple because of a unified chamber for all four strokes, but looking at the number of components and the actual maintenance for them....very complex. Ramjets are sweet because of their simplicity, but a turbofan...well...http://en.wikipedia.org/wiki/Image:C...-turbofan.jpeg

I'd try and repair a recip much faster than one of those. At this point anyway.

[HAL9000]

Actually, turbofans are still quite simple... or should I say they can be simplified. Turbine engines have reached the level of the radio controlled model enthusiast and some guys are actually building their own turbines.

[hitchface]

A radio controlled model engine is in a bit of a different league from a PW4000. For what they do, yeah, they are incredibly simple. There is, however, a reason why you need to have a lot more experience to be working on them as a job.

[HAL9000]

Sure, the engine is more complex, the principle behind that same engine is no different though.

[hitchface]

I'm speaking strictly from a mechanical standpoint. If I had to pick one of the two that was more difficult or required more training/time/money to work on, which would it be?

[Brad the best]

that doesn't look to bad , just a crap load of turbines and injectors .

im sure it would be simple if you got trained and worked on it for a couple years . everything looks complicated until you get used to it .

[kamikazi_tom]

Wow this turned into quite a thread. Anyways, my daddy fixed it. Sure enough, the govenor was bent and full of grass and other gunk. My dad cleaned it out and everything was good. Thanks to everyone that helped.

Tom =]

[Petef56]

Originally Posted by kamikazi_tom Wow this turned into quite a thread. Anyways, my daddy fixed it. Sure enough, the govenor was bent and full of grass and other gunk. My dad cleaned it out and everything was good. Thanks to everyone that helped. Tom =]

Thanks for posting the final solution!
It might help someone else with a similar problem.

---pete---