Small Engine Advice

[mayhem]

Saturday was my first chance to mow the lawn in about 2 weeks. I do my whole yards with a conventional push mower (21" Craftsman with a 6.25hp Honda motor). The mower has never given me a lick of trouble before, been using it for about 5 years now...its always been a 1 pull start. Grass was pretty long and thanks to a good application of springtime fertilizer its also quite thick now, so I was going along pretty slowly. After about 6-7 passes the motor just starts sputtering and it dies on me. Restarted right away and it happened again after a few more feet. It wasn't bogging down due to hevay grass, it was the motor just dying on me. Pulled the air cleaner, clean, oil level was correct and clean. Let it sit for a few minutes and it started right up again, only to die again after a couple more passes. At this point I'm thinking either an ignition problem, bad gas or something more serious like a scored piston wall.

Pet the motor cool off enough to get the plug out...it was a bit on the gross side but the electrode cleaned up ok, checked the gap and reinstalled, also pulled the air cleaner and sprayed the carb with gumout to see if I had any varnish stopping up the butterly...all to no effect, still crapping out on me. So I finally pulled the carb off and used the gumout on the intake itself, reassembled and fired it up. Spewed a cloud of black smoke for a minute and ran strong after that for a few minutes. Died again but when I restarted it I got a bog (for a single cylinder motor) backfire and got a pop of black smoke out of the exhaust that looked for all the world like someone fired a gun and it ran great for the next couple of hours.

So, based on what I've laid out here, I cna certainly swap out the plug and make sure its got clean gas...other than that, anyone have any useful suggestions? Small engines with carbs are not my forte, so apart from the very basics I'm a bit over my head.

Start saving up for a replacement mower?

 

[brad068]

sounds like gas cap aint breathing adequately resulting in vapor lock. try loosening gas cap when it stalls.

That might be possible, but to me it sounds more like a valve adj. is needed. With the hondas that I have dealt with this is a fairly simple job and it might be spelled out in the owners manual. When a motor gets a real good workout even if it is a few years old the heat, stress and wear will tweak parts especially in the valve train. When a engine is cold there might be enough clearance to get it started but as the combustion chamber heats up the valves expand and lengthen will in turn erase the already minute valve clearance. This will cause the valve to stay open minimizing compression and if/when the combustion charge does ignite it will send a bang out the exh. or back through the carb.

 

[quads]

Put a new spark plug in it, especially if the old one was full of carbon. Sometimes even if you clean a spark plug and gap it again, it still won't fire right.

 

[eba1225]

From what you say that the plug was gross, maybe that the motor is burning oil....was there smoke when it ran? Also it could be that it is running really rich, another sign of a ugly plug. On one instance, with the oil the deposits are hard and oily, with the gas deposits it is not oily.

As was said earlier you may have a fuel starvation issue (gas cap not venting properly), but that would be couterintuitive to the gas deposits.

I would start with looking at the plug deposits, oily or not. Oily is a sign of worn rings or bad cylinder. You know where this is going then.
If not oily then look into the gas cap, make sure it vents properly.
If the gas cap seems to be ok then it could be the carb is not getting enough gas (pump diaphram with the carb) is shot, need to rebuild the card. ( Know this one as I have a tiller that only runs on 3/4 choke as the diaphram pump is shot).

Let us know what you find.

 

[milner351]

I've got an old honda push mower that was previously a uhaul rental -- these things just don't die.

the gas cap is a great suggestion, as is a new plug - and put in anything but a champion - I've had nothing but problems with those - NGK is a good choice.

get the old gas out of it and put in some fresh stuff... hopefully that will do it....

 

[mayhem]

Replacing the plug is definitely a no brainer for me. It was not gunked up with oil, rather it was a dark grey and the crud that was on it came rihgt off with a quick pass of a stiff bristled nylon brush (on my gapping tool).

My guess is its probably running rich and has been from the day i brought it home as I've never done anythign except change the oil in this mower...its been remarkably reliable. Its never smoked except when I put the carb cleaner in there, so I'm reasonably confident that the internals are in good shape. I bet I'm giving up a bit of power and using more gas than I should be.

Anyone have a link to a handy "how to adjust your lawnmower cabeurator" link? I could use a good primer on how to do it properly...though for all I know its locked and has no provision for adjustments...there is no throttle switch...its on or off with the grab handle, though there is a butterfly handle that will rev the motor if you tinker with it...seems to be some sort of self adjusting mechanism as I can see it move back and forth on its own when I was spraying the carb out.

I'll check the gas cap too. Other than the backfiring it sounds very much like fuel starvation. No fuel filter to plug up...could be the fuel cutoff valve full of crap though. Have to check that too.

 

[New Hampshire Jim]

Mayhem: I had about the same problem with a snow blower. My fix and It did fix It was to spray Gumout into the gas tank A good shot of this about 1/2 OZ . Add new gas and let It run. The newer gas on the market will form varnish on the needle valve IN the carb and all the spraying around It will not get It out.Sometimes when a carb is rebuilt the needle is taken out and soaked in solvent to remove the gum By putting It in the gas you will blast It out. hopefully
Jim

 

[burntime]

Almost sounds like a condensor problem also. Gets hot and dies. Check the other things but also check spark when its hot.

 

[fbelec]

you have all good answers here. if it sputters a few times before stalling that will dirty up the plug. from there to get a good reading on the plug start it and run it with a clean plug. after it's been running about 10 minutes shut it off and pull the plug. that should give you a good reading on how it's running. in the beginnings of oil burning the plug will show gray. and not necessarily greasy. now i had the same problem on my sears mower a few years ago and it turned out to be a head gasket.

honda's are great motors but they don't like to be hot
good luck

 

[semipro]

I own numerous Honda-powered tools (mowers, roto-tillers, concrete mixers, etc) and suspect your problem is with the carb. If you can remove the fuel bowl I'd do that and then see if the main jet is clogged. A very small piece of junk can clog it up.

 

[mayhem]

Went to go tinker last night and when I tried to start it, the safety switch cable snapped right in the middle of the liner. Realizing god was trying to tell me to spend my time playing with my daughter instead of mowing the rest of the lawn I took the hint and got out the wiffle ball and a couple of squirt guns. One of the very rare summer evenings we've had this year...we decided to enjoy ourselves and let the work be damned.

 

[colebrookman]

sounds like gas cap aint breathing adequately resulting in vapor lock. try loosening gas cap when it stalls.

Just fixed my daughter's rider. Stalled and never would restart. Usually I would think of all the worst problems and start replacing and fixing until it runs. Something that many auto macanics like to do. This time I noticed how hard it was to remove the gas cap when checking for fuel. Pulled the cap, removed the inner rubber liner, blew through the small pinhole in the cap, replaced it and it's worked well since. Sometimes knowing to much and forgetting the basics makes things much more difficult. One mans way.
Ed

 

[tjnamtiw]

My first reaction was pump diaphragm in carb but when you said it coughed, blew smoke and then ran fine for hours, it sounded like a sticky valve after sitting so long. Condensor, if it has one, is a good guess too.

 

[glenng]

I`ve had this happen to me before. Water in fuel. Under full power the engine draws enough fuel from the carb float bowl that it sucks the wee bit of water from the bottom of the float bowl. Condensatation from storing the mower in an unheated place can cause this. Or leaving it out in the rain will if the Gas cap has a faulty gasket or vent hole on top.

Clogged fuel filter or partially shut fuel valve will cause similar problems as well.