Anyone do lawnmower or small engine repair? Question on no start

I've got a small mower with a briggs 12H802 motor that I can't seem to get started. I checked fuel flow to the carb and it flows well, filter isn't restricted at all. The carb has clean fuel in the bowl, but I took it all apart anyway and cleaned it. It was pretty clean and all the passageways and needle were clear. I checked spark on the engine by putting the plug against the head and pull starting, looked OK, blue-white color and jumped the gap fine. Timing is right on, the spark is just before TDC. The flywheel key isn't sheared, I checked it too. I pulled the head off and the valves look clear and open/close properly. Compression was good too. I tried starting fluid both through the carb and directly into the cylinder and it won't start with either. I'm wondering if it is a weak spark, but don't know if that is such a thing with these ignition coils or not. I'm stumped with this and don't know where to go next, it seems like there shouldn't be anything preventing it from running. One strange thing I noticed was the throttle cable handle doesn't seem to affect the butterfly position. I thought I put it together wrong, but another mower I looked at was the same (see pic of mine). Any ideas?

 

could also have a low oil shut off switch sticking. depending on its age if it has a handle safety to start it, it might not be working right or not pulling enough to let it start. The coils can and do go bad, if its arcing decent it should be loud enough to hear it. Its weird it has spark but doesnt light off or try to.

 

mine has two cables I think one for the start at idle and one for the front drive.

 

Did you try fresh fuel? And is anything like dried up grass obstructing the blade? It might also be a dirty ignition coil. Maybe try cleaning the coil and the flywheel magnets with rubbing alcohol or some other solvent. If you're getting a weak spark it could be due to too much insulation (dirt and crud) on the coil or magnets.

I had to replace the coil on my mower years ago. The engine continually stumbled for a few weeks before the coil finally died. I wasn't getting a spark though so my symptoms are a bit different than yours since you're getting spark.

Good luck,
Steve

 

Thanks for the replies. I don't think it's the safety switch because that would ground the plug and prevent it from sparking at all. It spins pretty well with the pull cable. I cleaned up the flywheel magnets so they are nice and shiny and it's got brand new gas in it, still nothing. I might just change the coil, it's like 50 bucks but I don't know what else to check.

 

Make sure the air filter isn't plugged?

 

Honestly there are so many things that it could be. Internet mechanics won't always be able to diagnose it because some things you need to hear. The list of little things is so long that we would be asking you for weeks to check this or that. Take it to someone local with a good reputation and start there.

I have had friends text me at work for similar diagnoses and get no where. Get home from work and I can fix it in minutes now that I can actually see it. Some questions got me answers that didn't match once I saw it in person.

 

Here it is after a new head gasket, piston/valve cleaning, carb rebuild, and a new air filter. Runs perfect for a while then starts this, seems to misfire when it gets hot. Any ideas?
https://www.youtube.com/watch?v=0P1Czuag7OY&feature=youtu.be

 

Was that from cold? If you start it again will it run a few seconds before doing it again?

If it will do it repeatedly each time going a few seconds like your video but after stopping and starting it again it clears out before doing I again I would replace the fuel line. Old fuel line will sometimes separate the inner from the braided section. Then it flows slowly filling the bowl so it starts and runs for a short time then starves for fuel. You shut it down and it starts fine again before draining the bowl faster than the line can fill it. This may not be the issue but I have had this happen enough times that when it starts fine before acting up I start there. It has been the sole and only cause enough times.

 

Sounds like how it's acting fits that exactly so I picked up some new line after work. Hooked it up without the fuel filter just in case it was plugged (looked clear though) and it did the same thing again. I even pulled the fuel cap in case the vent was plugged but it didn't help. For as simple as these are this is really perplexing me

 

Forgot to mention I ponied up for a new ignition coil. Didn't help either lol

Might try a valve job next. That's pretty cheap. Valves are only $5 each so I won't have to grind the old ones. Just lap and set the clearance

 

Did you empty out tank and put fresh non ethanol gas in?

 

Sorry that wasn't the source of your frustration. It is an easy fix to eliminate at least one simple cause that otherwise would slip by troubleshooting. I didn't see if you replaced the plug or not. When in doubt new plug always. I have seen new and old plugs do goofy things.

This may require a trip to a small engine mechanic. Without it in my hands to check each and every tiny thing I don't know where to direct you next. You are hitting the right things. Before the valve job try a compression test and then a leak down test. Leak down you pressurize the combustion chamber through the spark plug hole and try to determine if and where you have significant leakage. There are pretty expensive kits for this. Basically you need a regulator, a compressor and a line to the spark plug hole. You MIGHT get away with a rubber tipped blow gun but then again I have the stupid expensive kit so I don't ever try it that way. So you make sure the valves are closed and the piston at top dead center. Pressurize and listen for leaks and then determine if the exhaust or intake is leaking by checking the carb or exhaust for air flow. If the leaks are coming into the crankcase you can hear it at the oil dipstick which indicates a worn ring (or a cracked cylinder or anything allowing the air into the crankcase). By doing this you may be able to eliminate the valve job before chasing your tail some more.

One last thing. Did you carefully blow air back up the line to the tank? If you had a big or some other garbage in the tank blocking the tiny hole to the fuel line it can restrict the fuel flow as well.

 

I put in fresh gas of the normal stuff. Unfortunately can't get pure gas here anymore but I've always used 93 which has up to 10% ethanol per the pump.

I put in a new plug at the beginning of all thus but I will try a new one because I could have fouled or damaged it during some of the other work. The original leakage test was about 30% on a cold engine, but that was before replacing the head gasket. I'll see if I can borrow the tester again this weekend and if the results are any better. I took the tank completely off and flushed it out with carb cleaner. It was pretty clean inside and flowed out the port well. I'll take a look inside the carburetor and see if it's restricted at the inlet but it was cleaned out well before.

I've probably spent more time on it than its worth but it's been a learning experience so that's OK. Appreciate the helpful replies. Will report back if I find anything this weekend

 

Coil breaking down when getting warm is where I would look.

 

OP replaced the coil.

 

Maybe the exhaust air flow is partially blocked. Have you tried running it without the muffler / spark arrester (just not near anything dry and flammable) to see if that makes a difference. It seems that you've tried just about everything else.

 

What he said^
Maybe something got into the muffler (Seen it happen before)
Are you sure you're getting a strong enough spark?

 

Tru-Fuel might help. Lowe's, Ace Hardware or Home-Depot sells it. I use it for all of my lawn equipment.

 

Didnt read through....
Pull the banjo bolt off the carb bowl and clean the passage in the bolt. When they havent been serviced regularly, the passage on the bolt starts to clog up. Sometimes when they are serviced, this does get missed.