Lawnmower Won't Run Under Load

[PDJetta]

Since I am stumped about this one, I thought I would ask the experts on this list. Here is the history of the problem:

This is my mother's Honda 4-stroke self-propelled "push" mower, about 6 years old. Last year my son was mowing her grass with it and tipped it up on its side to clear out some grass. The mower failed to start after that. I took a look and determined it was flooding, since gas was being spit out of the muffler when pull-starting it (could also get it to run by turning the fuel valve off to run it dry and then crack the valve a hair), but turn the valve on, it flooded and stopped) Ah, stuck float, I thought. I removed the carburettor and opened it up to check the float and float valve. Everything looked OK. Still flodded. Put a new carburettor on it (only $16!). Same thing--flooded. Then I discovered the flooding was because of the oil soaked air filter element (from oil flowing through the breather pipe when my son tipped it over, coating the filter and plugging it solid so air would not go through it). Replaced the air filter and it would run, but after warming up, under load would loose power, backfire through the carb and finally cut off. I put on the old carb. Same thing. Would not run warm under load. I then replaced the carburettor mounting gaskets (I reused the gaskets when I replaced the carb). No change. Took it to the lawnmower shop. They replaced the carburettor mounting (intake) gaskets again and said that was the problem. The mower then worked for a couple of weeks and then began doing the same thing.

I do believe it is a fuel problem, not an ignition problem, because when it begins cutting out, if I engage the choke, it will come back to life and run (although too rich to use). I can modulate the choke and it kind of runs. I also checked for a kinked fuel line from the tank and also looked for a fuel filter, but I do not see one. I would suspect a plugged carb jet, but with two different carburettors it does the same thing. Any ideas? I have spent hours working on this and am at a total loss as to what is going on.

Is there a sure fire way to narrow it down to a fuel or ignition issue?

Thanks.

--Nate

 

[MonsterTDI09]

Sound like you have a intake leak or weak/ crack coil or s/p wire, and check if the s/p not loose and the gap is ok.good luck

 

[eddif]

Spark ignition wonder how that works?

Things that have caused me problems:
Refusing to put in a new spark plug (or the second one).
Forgetting to check the shear key on the fylwheel.
Having a plugged main jet (completly plugged and / or partially plugged)
A choke control adjustment that never quite pulls off the choke (does not sound like your problem ... unless you have two things wrong)
Broken spiral coil on valve spring
Water stopping / swelling up paper fuel filter
Crankcase breathing system gone crazy
Crankcase with gasoline dilution
Crankcase with water dilution

Rigging that worked:
Close the spark plug gap to about .015"
Crank on propane till carbon or oil burns out (4 stroke only)

Parts swapping that saved the day:
Another coil (lately a Honda coil for a Kawasaki)

Always love cranking till I am about to drop. Grace just sometimes hits and things go to working.

eddif

 

[leicaman]

You may have to reinstall yet another carb kit. Did you shake the float when you opened up the carb? If it leaks you will not get a proper fuel mixture. When you shake the float you should not hear fluid sloshing in the float. I had a mower once do that and it really acted poorly. No power and really didn't run right. Also make sure the carb linkage is properly setup as per a manual which I hope you have. Also if there is a vane like a briggs for the governer, that might be stuck which also would cause a power issue.

Yes and as edjet said, a bad fuel line can also cause issues. The ethanol in today's fuel is hard on older small engine stuff, so replacing that fuel line could be the ticket.

 

[steelmb]

a pic of the intake system would be nice.

 

[edjet]

I know these carbs are cheaper to replace than to rebuild, and the Honda Tech told me it cost more to try to clean out the small orifices in those carbs successfully than to replace, so put another carb on it.

I also noticed my fuel line deteriorating, so I changed it and installed an in line filter. Make sure that your fuel line is not getting to hot causing a vapor lock ( not likely, but possible). Your ignition could also be the problem if there is a heat issue causing a breakdown in that system.

I recommend getting another mower, I am not happy with my Honda. Get a good old
Briggs motor and use Stabil in your fuel all of the time.
Good luck.

 

[White Crow]

If you have to use the choke to make it run it's lean. I don't know what turning it on it's side would have to do with it (other then oiling the filter) but if there is even a tiny bit of trash in the main jet it will run lean and I would guess it's CA. compliant so there is no adjustment. If there is fuel in the carb it's not a supply problem. Honda mower engines have adjustable valves under the little tin cover if the intake valve is too tight it will backfire and run poorly.

 

[Souzafone]

2 things I didn't see you mentioning, fuel pump and choke pull off. I'm not familiar with the Honda set up in particular, but what you describe sounds like a typical pulse type pump failure. If this uses either a vacuum or mechanical pump, I'd be willing to bet there's a problem with the internal diaphragm, either sticking or being holed, where there's just not enough pressure. Choking it helps a little because you increase the fuel to air ratio. My thought about the choke pull off would be strange, I'm wondering if it would be possible for it to have filled up with fuel when it was tipped over, and it could mimic a stuck float situation? Is there a safety system that shuts the fuel when the engine is tipped? Just guesses, good luck.

 

[Ski in NC]

Some engines have a little screen on the fuel tap in the tank. Disconnect fuel line from carb and make sure you get good flow. If not a little burp of compressed air up the line can dislodge the crud from the screen.

If tank is above carb, there is probably no fuel pump.

Second that about the main jet. If it is lean, there is probably some crud in the jet.

 

[PDJetta]

Thanks everybody! That is why I love this list: Great suggestions, some of which I forgot about and others which are new.

"If you have to use the choke to make it run it's lean. I don't know what turning it on it's side would have to do with it (other then oiling the filter)". These were my thoughts too.

I know the carb float is not leaky.

The possibility of a broken FW shear key I'll have to check. It acts as if the ignition timing is changing as it is loaded (begins backfiring through the carb). Same with the possibility of a broken (intake?) valve spring.

Maybe the breather got plugged somehow. I'll check that too.

I probably should replace the spark plug. It is pretty sooty from me running it on choke while trying to figure out what is going on. The oil smells of gas too.

The linkage appears intact and the governor appears to increase the throttle opening as the engine slows under load.

The carburettor has an adjustment screw on it (has a limiter, I think). I'll fiddle with that too.

"2 things I didn't see you mentioning, fuel pump and choke pull off. " I do wonder how the fuel gets metered through the main jet. The float bowl is gravity fed from the fuel tank (fuel flows freely through the line). The vacuum created from the air flowing through the venturi must draw fuel up and through the jet, so there may not be a vacuum-operated (fuel) pump diaphragm, as I have found on small engines that have the carburettor mounted on the top of the fuel tank.

But when I removed the carb the second time, I noticed a passage in the carb spacer that I figured was the bowl vent. I originally used Permatex sealer on the old mounting gaskets (since I did not have new gaskets) and I think I may have plugged this passage. I thought that was the issue and cleaned off the spacer and was spotless with my use of the new gaskets. Still did not solve the issue. Maybe I'll see if I can get the old carb apart and see if there is a diaphragm in it and just put the new carb back on with new gaskets and make doubly sure the spacer passages are clean.

I figure if all the above checks out, if a new magneto is not too much, I'll put one on.

I should also price a shop manual for it.

--Nate

 

[s4phillips]

I had a Kawasaki powered JD mower run very similar to your situation: it was the spark plug. I was down on myself for not doing the obvious/simple things first. Pulled the carb and entire fuel delivery system off multiple times before finally replacing the spark plug.

Gravity feed fuel systems do not have any fuel pumps, so no diaphragms. You should have one or two bowl vents - they probably just have a small tube attached that just routes down the side of the carb and hang free and open - make sure these are not clogged.

Have you checked the oil level? It may have been raised with fuel and it is getting too much oil in the combustion chamber. Does that setup have a crankcase breather routed to the air filter housing? If yes, is it clear and allowing the crankcase to vent?
Also, make sure the spark plug cap and the connector on the spark plug are not corroded.

...if there is ever a next house for us, I am thinking it may be sans grass and mowers!!!

 

[lovemybug]

This sounds a lot like my old Honda snowblower is running. I'll have to change the plug and see if that makes a difference. It's possible that the points could be getting worn, too. This thing is approaching 30 years old, I think, so it's possible that something could be getting worn on it. I, too, need to get an actual shop manual for it, not just the owner's manual.

 

[PDJetta]

I Googled this very issue and I found several accounts of Honda mowers exibiting identical symptoms. Some never found a solution, but several stated that simply replacing the spark plug curred this. A few went through quite a list of parts replacement before replacing the plug. The plug in mother's mower is covered in soot from the oil-soaked (clogged) air filter causing the engine to flood. I just wonder if all that carbon causes the spark to misfire under load. Carbon is conductive. Before I tear into it again I'll replace the sparkplug. I never would have thought it could be the sparkplug.

--Nate

 

[s4phillips]

snip... The plug in mother's mower is covered in soot from the oil-soaked (clogged) air filter causing the engine to flood. I just wonder if all that carbon causes the spark to misfire under load. Carbon is conductive. Before I tear into it again I'll replace the sparkplug. I never would have thought it could be the sparkplug.
--Nate

Yes, carbon and oil coating causes the spark to find an easier path to ground than jumping the gap as it should. In the really old days of two-stroke engines this was much more common with crappy oils, ignition systems, tuning, along with very basic spark plugs. When you hear someone refer to a fouled plug the carbon and oil coating has choked the plug - can also happen to four-stroke engine.

 

[LiLredTDI]

Funny this thread is here, must be something in the water.

I bought a pressure washer new about 2 months ago. (briggs/stratton 1150 model with a 3500 PSI rotary pump) used it a couple of times over the course of a few days with no issues. Added some sta bil to the tank and stored her. Took it out of the shed yesterday to use it and it fired up and ran, but as soon as I pulled the trigger putting it under load the motor cut out. Inspected the linkage and "looked" as if one of the fuel line hose connectors was interfering with the governor linkage. Removed the fuel tank and tweaked the clamp and reassembled. Fired up right away, pulled trigger and it died. Tried to start it back up and it would run 2-3 seconds and die and backfire through the carb. Guess I will have to change the plug too.

 

[Drivbiwire]

If the engine runs fine at idle (high idle) without any load The issue is the governor.

Check the linkages and the governor arm motion at various rpms.

You could have lost a flyweight spring or have something binding it up.

 

[Drivbiwire]

Tried to start it back up and it would run 2-3 seconds and die and backfire through the carb. Guess I will have to change the plug too.

Clogged main jet...

Get some copper wire, insert in main jet, and floss it out. Reinstall jet, good to go.

Option B: Ultrasonic cleaner, works wonders on carbs!

 

[D-Cell_Mekanick]

I had a problem with the crankcase to carb hose being dry rotted making the engine hunt under load. May want look into that.

 

[greengeeker]

Funny this thread is here, must be something in the water.

Seems while most on here complain about misfuels in their TDI, my wife decided to fill up our lawn mower with a 50/50 mix of D2/87oct I had ironically removed from a TDI. Yes, something is definitely in the water.

 

[eddif]

Seems while most on here complain about misfuels in their TDI, my wife decided to fill up our lawn mower with a 50/50 mix of D2/87oct I had ironically removed from a TDI. Yes, something is definitely in the water.

I suggest only a 25/75 mix for the mower. LOL


eddif

 

[turbocharged798]

I put some diesel/unleaded mix(that my dad accidentally put in our 99.5 months ago) in our 12HP garden tractor. Doesn't run that great on it actually. Smokes enough to kill every mosquito around. Just don't have anything else to do with the mixed fuel.

Probably should run it in our piece of crap dumpster find generator and actually make electric with it.

 

[PDJetta]

Unbelieveable! It was the spark plug! I replaced it with a $4 brand new one and end of trouble. Mowed half an acre, under a good load. For grins I then installed the old spark plug and after a few minutes, after the plug got good and hot, the engine faltered, backfired throught the air cleaner, and cut off. Put the new plug back in, finished up mowing, no issue.

I NEVER would thought a bad spark plug would cause the symptoms I experienced. The plug looked new, EXCEPT for all the black soot on it. Carbon does conduct electricity and I could see with a loupe where the spark arced to the insulator, due to a big white spot on it amongst the black soot.

So it was two issues: 1. my son tipping up the lawnmower to clean grass out, which caused oil from the breather to completely soak the paper air filter, completely plugging it. Attempts to start the engine caused gas to flood the engine (spit it out the muffler) and once it ran a little, it carbon fouled the spark plug. I then replaced the carburetor (thinking that was the issue) and then discovered the air filter is plugged and replace that and it ran, but began cutting out when warm. Remounted carb with new gaskets and used gasket sealer and no change. Sent it to the lawnmower shop and was told it was not running right because I used sealer on the intake gaskets. They replaced the gaskets for $45. It ran OK for a week and began doing the same cutting out and quitting. The lawnmower shop could not even figure it out.

Just a plain soot fouled $4 spark plug and about 20 hours of my time over two mowing seasons trying to figure this one out!

--Nate

 

[ymz]

Oy vey...

Now I have to start keeping spark plugs in stock for my lawn mower, lawn tractor, and snow blower ??????? (And don't even remind me of carburators... bad memories of my first car... Type-III Variant with dual carbs... I should really say "duel" carbs, as they never quite got along with each other... except at WOT... that car could move... when it wanted to...)

Yuri

 

[PDJetta]

This is from the NGK web site. Confirms what I experienced:

Q: What is a "fouled" spark plug?
A: A spark plug is considered fouled when the insulator nose at the firing tip becomes coated with a foreign substance such as fuel, oil or carbon. This coating makes it easier for the voltage to follow along the insulator nose, leach back down into the metal shell and ground out rather than bridging the gap and firing normally.

"Finally, a dirty air cleaner can create a too-rich condition which can lead to fouling.....but, once a spark plug is fouled, it will not provide adequate voltage to the firing tip and that cylinder will not fire properly. "

This is what happened in my case, oil soaked the paper air filter, completely plugging it so the engine flooded. The spark plug was black with soot, but I thought nothing of it!

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqfouled.asp?mode=nml

Funny, the mower uses an NGK plug as OEM!

I was getting ready to replace the magneto as my next task!

--Nate

 

[turbocharged798]

That's why you don't tip a lawn mower over more than 45*. Drives me nuts when people turn it over on it's side without draining out the oil.