More small engine issues...

After seeing the other JD thread, it inspired me to vent my current issue. Due to lack of time I havent troubleshot anything thoroughly but more ideas are good...

Last time I mowed the engine seemed to be a little jumpy bit it was 90+ and nasty humid so I didnt tink much of it because I didnt feel too well either. Go to mpw this week and upon blade engagement, engine starts missing a little. Give it some more load and massive misfires. Hm.

Change the plug and fuel filter and no change. Pull air filters and no change. Disengage the blade and its not missing so bad... Hm.

So, bad gas? Need valve adjustment? Carb issues? Ignition? Odd load problem elsewhere?

I was going to use some other gas but after that I really dont know what to try next besides replacing random parts. Help me not spend money!

Z225 with 18.5hp Briggs 31p707

Back in the day I would recommend adjusting the carb slightly richer, however I doubt your carburetor is adjustable.

When your engine acts up, try pulling in the choke incrementally and see if the engine runs better. If so, then you’re looking at carb troubles.

Sometimes the simplest fix is a loose carburetor…. I have seen plenty of those.

Let me guess, its smoking too? Oil smell like fuel? The briggs 31 series is a notorious head gasket blower, right between the bore and pushrods. The latest gasket seems to hold up, if you oil the bolt threads and torque it right.

Or its plugged up or has a vaccum leak and leaning out.

Funny, I had the exact same problem with a Briggs 18.5 Intek (same engine). If it isn't the head gasket like Kenny said, then it may be the Nikki carb itself. If you remove the fuel bowl, you will see the lower half is plastic, which is removable. Either the o-ring gasket under it (between the plastic and aluminum carb body) or the plastic has a problem. You can get the lower parts in a kit or the whole carb (best prices on ebay it seems). That seems to be the solution for the carb issue.

I have a different engine on mine right now and my Dad has the Intek apart, as it had a rod knock as well. So we haven't had a chance to confirm if the carb will work better. But it seems to be the most common problem with them per the internet.

My suggestion would be to start simple:

1) Get a bottle of Stabil Marine formula for ethanol fuels

2) Fill fuel filter with it

3) Double or triple the recommended dose in the tank.

4) If accessible, drain float bowl.

5) Check to see if engine runs better after warming up. It may be gradual improvement, but will be noticeable.

I ran into a water in fuel problem with my craftsman with a 20hp briggs. Between getting rained on and humidity it would start but ran rough, needed partial choke to keep running (how much needed would vary).

The steps above along with treating the can I use to fill the tractor with resolved the issue. Been running good for about 6 weeks now.

Modern ethanol fuels. This is my job at Home Depot... repairing people's stuff. It sounds like an exaggeration, but easily 90% is fuel related.

Ethanol absorbs water. Its shelf-life is about 30 days in a vented tank, 60-90 days in a sealed evap tank like yours, or like a car. It absorbs water and then attacks brass and aluminum making a white, chalky junk that gums things up.

Head gaskets are a common failure on those Briggs, but start with the simple things. Fuel first, then test spark. Hot blue spark is great, but any yellow or orange in the spark and you can bet the coil has a crack in the epoxy. A good test for that is to remove the coil and put it in a 200 degree oven for 20 minutes. Reinstall. If it cures (or partially cures) the issue, time for a new coil. Before you check the head gasket, pull the flywheel. Its unlikely that you sheared the woodruff key since you don't have a direct connection to any implements (like a push mower would) but Briggs uses really soft steel for those keys. If it wears a bit, your spark timing could simply be off a bit.

I'd check the carbonmaker first thing too. I've seen ethanol attack various fuel system parts, but there's plenty of people on teh int3rw3bz who will holler that's a bunch of hooey. Had someone on this here forum holler in caps he was sick of hearing about it 'cuz it wasn't true.

I had the JD thread yesterday...why can't they build small engines that run for 30 years without any problems, even if you're a nitwit and don't even change the oil? Seems the basic, flathead one-lung lawnmower engine has become a dinosaur.

I get that cars have become more complex- we want faster, more comfortable, safer, more efficient, etc. But a lawnmower's job is to do one thing- mow the lawn.

And what's with all the mega- power engines these days? My dad just bought a lawn tractor - a lawn tractor- with a 27 horsepower engine. That's 1/3 the power my car makes, to simply putter around the yard at 3 miles per hour and chop a couple of inches off the top of thousands of little weeds. Oh, and it burns something ungodly like 2 gallons of fuel every hour. Tuna's 15 hp job uses (according to him) 1/2 a gallon per hour. I had an old flathead 12 hp mower that would run seemingly forever on a dinky little plastic tank mounted in front of the steering wheel. Now they have to put these odd-shaped injection-molded 5 gallon cells wedged under the seat and above the transaxle.

/rant off

Missing under load...definitely sounds like a mixture or spark issue. I like the choke trick suggested above- I've also built little carb blocker plates to install between the air filter and carb on these newer engines with non-adjustable carbs as a troubleshooting tool. They always tune these things right to the brink of too-lean from the factory, so any little bit of restriction in the gas supply and the thing won't run right. A carb rebuild may be in order.

I'd go after the mixture issues first- I rarely have found spark problems on small engines. Mixture issues seem to be far more common.

Here is a good sight on rebuilding the Nikki carb http://outdoorpowerinfo.com/repairs/briggs_intek_single_ohv_nikki_carb.asp

You can see the problem o-ring gasket in the 7th picture, well at least the one giving us problems.

Volvo, you are right, the old flathead style ones run forever, we replaced the Intek with an older Briggs twin 16 hp, no problems now.

Simplest thing in storing any fuel is to use some Stabil before putting it away. I do that with my Craftsman mower and my Tecumseh powered snow blower. I have never had a fuel problem with either. The mower is 25 yrs. old. the blower is only 17 yrs. old. Yes it is ethanol fuel.

Fuel is only ~4wks old and at least the first bit worked ok. I will get some stabilizer and give that a shot. Worth it.

Thanks for the carb links, very helpful.

I sprayed the coil and wire with a water mist, no arcing at all.

I will try and let it warm up more as well and see if that helps.

Gotta get one more mow in tomorrow if possible.

Messed around with it a bit more.

Comp = 140-150psi warm Spark looks good Added fuel stabizer Checked ease of turning crank manually - good Checked for loose carb/intake parts - good Tried to block off intake to see if it richens - same behavior Pinched the fuel line - no change, odd?

Hm. I can drive it with no issue as long as the deck is disengaged. The only thing I didnt do is lock the deck somehow and see of something is jammed. Or its just enough load to poss something off.

I'd drain the float bowl just to make sure there isn't water in it.

Check the valves? What spark plug do you use?

Good call.

I use the factory spec 12yc I think. Didnt chek the valves but with that comp, it wouldnt be my next suspect. Its almost due for valve adjustment though...

I personally have bad luck with any plug that isn't Bosch or NGK. You might try the x ref.

The only two I can find at the moment are the OE Deere and a Champion which is what I used.

What sort of governor does it have. If it has one.

I am sure it has one but I know little in this area. If the carb is bad, Megasquirt?

http://www.sparkplug-crossreference.com/convert/CHAMP_PN/J12YC NGK BP6S would be good.

Megasquirt has been done on one bangers before, just make sure you have enough electricity to run it and charge the battery.

Ok, I will give that plug a try. Might buy the carb rebuild kit so I have it for when I get back.

The ms power draw isnt much, the fuel pump and injector will be though!! The only spare pump I have at the moment is an 044...

If this was a handheld (weedwacker, blower, etc.) I would say check the primer bulb or the fuel pickup line in the tank as it sounds like you are getting extra air under load/high rpms. It may seem silly but how old is the fuel line from the tank to the carb? Also check the o-ring behind the carb to the intake manifold/block.

Cleaned the carb. Some buildup but not bad. Still did it.

Unplugged the deck clutch, engaged, still misfired. Wtf.

After some digging looks like my seat safety switch was starting to go bad (high resistance) and triggering the fuel shutoff intermittently.

Jumpered it and all is well. Insanity.

I just eliminate that junk as it fails. For a while the backup mower only had one wire, to a kill switch on the dash.