My lawn mower hates me, please help

Our lawn mower is a Lawn Boy model 10655, the engine is a Honda GCV 160. Last fall it started to act up- namely it would start fine, run for a few minutes, then stall. Same behavior if cutting grass or sitting there running. I got it to run long enough to finish what I had to do by forcing the choke to stay "on" just a bit, then I shoved it in the garage and forgot about it.

Well, it didn't fix itself over the winter. And now I'm puzzled as to what spirit has possessed it.

The choke lever is spring loaded. Pull it back to choke it, and a spring returns it to its normal position.

There is no manual throttle control, it magically regulates itself.

These are the basic parts that control the carb. These have been modified by me, they are not in the stock state.

What is happening is the mower starts and runs for a bit, during which you can see the "throttle control lever" move to control the engine speed. After a few minutes, it starts to move back and forth more and more until the engine finally quits. The only term I can come up with to describe it is hysteresis- it's like it's trying to make adjustments, but they become more and more exaggerated.

So I attempted to manually fix the throttle by using a couple nuts and a bolt. I started it, adjusted the nuts and bolt to where the engine sounded right, then it would stall shortly after or over rev terribly.

berkeleying magic.

Anyway, I did the following:

• Checked the air filter, it is good (clean)

• Checked the spark plug, it looks good

• Looked for a fuel filter, there isn't one I can find

• Took the air filter and carb off, cleaned them both. The carb looked brand new on the inside. I put new gaskets in and reinstalled everything.

• Drained the gas tank and put new mid grade fuel in

Does anyone have any ideas? I'm in full-on WTF mode here.

Sounds like it's lean surging, not enough fuel so it runs, dies, governor jacks the throttle open, it catches again, and cycles like that. The ""throttle" control lever" is the governor arm, it's movement varies with RPM in such a way that more RPMs causes it to pull the throttle shut. A spring counteracts this and sets the engine speed, on small engines with adjustable speed all the "throttle" does is adjsut the tension on the spring, more tension=more RPM, push mowers with larger (20+ inch) blades are usually set slower than the standard 3600 rpm max engine speed.

I would guess you either you missed something in the carb or you have a fuel flow issue to the carb, gas should stream out if you yank the hose off the carb.

I'm pretty sure the strainer inside the tank on my Honda snowblower is mostly plugged. Same issue- pull the fuel line off the carb, it will flow nice for a second or two, the gets really slow.

Make sure the vent in the gas cap isn't plugged, too. That would take more like 5 or 10 minutes.

Sounds like typical trash in the carb behavior. Did you blow out the fuel line? Maybe there's still some junk in there.

Streetwiseguy wrote: Make sure the vent in the gas cap isn't plugged, too. That would take more like 5 or 10 minutes.

This occurred to me right after I posted the thread, so I went out and checked that. Cleaned it all out, and nothing looks to be blocked. I even loosened the cap some while it was running, it made no difference.

Thank you, thank you all for the input! I really appreciate it.

Interestingly enough, parts for this thing are only available at an authorized Honda dealer. I'll go through it all again tomorrow and be sure to blow everything out with air.

In reply to paranoid_android74:

Remember, if you have floaty swarf in the tank, and you blow it off the screen, it will migrate back fairly soon. If you blow back through the tank and it works better, you should probably pull the tank and clean it.

I don't know that model, on pre-mix it'll do exactly what you are describing when the mix is bad.

Check the tank vent. When it starts running poorly, pull the cap, which is where the vent is.

When you cleaned the carb, did you run a wire up through the jet? Ethanol and brass like to make white crusties in the jet and just spraying cleaner through it won't do the trick. I used to work in small engine repair, and I probably did 300 units. I've never encountered one that wasn't a carb issue. If it took longer I would say its a coil issue; coil heats up and quits, but I'm pretty certain you have a carb jet clogged.

No need to take it off again, just pull the bowl and poke a paper clip or strand of copper wire up there. I keep a set of welder tip cleaners around my shop for that exact purpose. They're just little round files in gauged sizes.

Also, how did you clean the air filter? Just compressed air? Or solvent? Some solvents leave junk behind after the carrier evaporates and they don't flow air. I agree that it sounds like a lean condition so I doubt that's the issue, but its easy to check; just take the air filter out and see if the problem remains.

Curtis makes a very good point about running a wire (welding tip cleaner preferred, available most places welding supplies are sold, TSC, LowesDepot, metal stores, gas stores, etc.) through the jet, avoid removing material but don't worry about enlarging it ever so sightly, these are jetted pretty lean from the factory. I prefer to remove the jet but you'll need to grind the sides off a cheap screwdriver to get the proper sized blade in there to break it loose and not mangle it, I think a long 1/4 inch hex drive screwdriver bit like you'd run in a drill might work to.

I have a newer Honda self propelled mower with the GCV 160. It has an auto choke thingy on it. Usually it works pretty good but sometimes it likes to try and turn the choke on for a hot start (like after emptying the bag for example). It makes it run super rich for about 5-7 seconds. The auto choke and govenor fight each other so it surges for a bit. I let them duke it out before I start mowing again. The auto choke concedes defeat and then it runs fine. Does yours have the auto choke system thingy? It might be sticking or something? Its kind of a goofy system but it seems to work alright most of the time.

Did you check for a banana in the tailpipe?

I agree with the others here saying it a fueling issue. Either a clogged screen or jet. The gas cap vent being clogged and air filter loaded are also possibilities.

I don't know if it has it or not but I have seen a few of the super quiet mufflers get clogged from crap. If everything else mentioned is good, check that if it has that style. This has a 0.05% chance of being it.

A friend's mower was surging while running (constantly up-down-up-down on the RPMs, independent of load) and it was the diaphragm in the carb. Replaced and it ran 100% perfect. Not sure it's the same problem but it was an easy fix and the diaphragm was super cheap.

curtis73 wrote: When you cleaned the carb, did you run a wire up through the jet? Ethanol and brass like to make white crusties in the jet and just spraying cleaner through it won't do the trick. I used to work in small engine repair, and I probably did 300 units. I've never encountered one that wasn't a carb issue. If it took longer I would say its a coil issue; coil heats up and quits, but I'm pretty certain you have a carb jet clogged. No need to take it off again, just pull the bowl and poke a paper clip or strand of copper wire up there. I keep a set of welder tip cleaners around my shop for that exact purpose. They're just little round files in gauged sizes.

Why is this not in the 'tools I can't imagine to live without thread?"

I think I have one of those somewhere.

What? I can't hear you, I have bananas in my ears...

Again thank you all for the input!

I agree, I'm having a fuel problem.

Sunday I:

• tested fuel flow from the tank to the shutoff. It was very good.

• tested fuel flow from the shutoff to the carb. It was very good.

• confirmed there was fuel in the carb bowl.

• took the tank and carburetor off again.

• cleaned the aforementioned items with compressed air and carb cleaner.

• removed the jet from the carb, cleaned with air and cab cleaner. Made sure I saw daylight through all orificeseses.

• put it all back together tonight and ran it.

I think this fixed it. I can't be sure because I modified the original governor linkage and lost one of the springs. With the self turning off choke closed a little, it ran like a champ- didn't stall once.

Maybe if I can find some governor replacement bits it will work again!

FlightService wrote: Did you check for a banana in the tailpipe? I agree with the others here saying it a fueling issue. Either a clogged screen or jet. The gas cap vent being clogged and air filter loaded are also possibilities. I don't know if it has it or not but I have seen a few of the super quiet mufflers get clogged from crap. If everything else mentioned is good, check that if it has that style. This has a 0.05% chance of being it.

curtis73 wrote: Also, how did you clean the air filter? Just compressed air? Or solvent? Some solvents leave junk behind after the carrier evaporates and they don't flow air. I agree that it sounds like a lean condition so I doubt that's the issue, but its easy to check; just take the air filter out and see if the problem remains.

I forgot this part- I gave the air filter a shot of air to clean it. It really wasn't terribly dirty.

I'd recommend picking up a cheap laser tach to ensure you haven't screwed up the governor calibration, mine is a ~$11 "DT-2234C+" off ebay that works really well, extremely accurate and a lot less finicky than the cheap inductive tach/hourmeter boxes you can buy.

Have you tried something like this to blow out all the tiny holes and the gas lines?