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I encountered a weird issue with my backup Troy Bilt riding mower the other day. I don't have the engine model number if that matters but it was built in 2009 and is 17.5 hp Briggs engine.

While waiting on a new deck spindle for my Craftsman (Husqvarna), I got it out for the first time since fall. I don't really like this mower because I'm too used to the hydrostatic transmission on my Husqvarna and it's awkward having to come to a complete stop to speed up and slow down around trees and shrubs.

Initially it was running OK. But over time it got to where it sounded a bit rough at times. Then I shut the engine off to chit chat with my father and afterwards I noticed fumes coming out of the muffler. I thought the thing was going to burst into flames! Then I noticed gasoline starts filling the neck of the air cleaner. I've seen this happen before, a stuck float valve.

So I took the carburetor off and pulled the fuel bowl off and discovered the float would not pivot. I noticed the float is made of a cheap white plastic material instead of brass.

So I removed the float and float valve and cleaned them and passages with carburetor spray cleaner. I put the carburetor back together and tested it upside down and so forth to make sure the float was now working. But that was not all I had to do. The crankcase was full of gas and the spark plug was carbon fouled from running rich. So I had to change the oil (which it needed anyway) and I bead blasted the spark plug. Yes I realize your suppose to replace spark plugs anytime something happens but I bead blast my plugs and recheck the gap. It's worked fine for me for years.

While I was at it, I also replaced the fuel hose and fuel filter.

So I finish my mowing and put the mower up.

So I get it back out a week later and for some reason the mower will turn over but not start. I checked the oil level to make sure the float valve is seating. Level is fine. I get out some starting fluid and it fires right up and idles and runs fine otherwise. I let it run for awhile, shut the engine off and it once again won't start. I check the choke operation while running and the engine bogs down with the choke on so I know the choke is working.

So I decided to check the spark plug. It looks fine to me but I wondered if the spark plug has anything to do with this problem.

I pulled the spark plug out of my 21 HP B&S engine. Now the mower fires right up!

So why would the engine require starter fluid to start on one spark plug but not another? Even thought it looks clean could it be getting weak causing a weak spark?

If the spark plug is not the issue, then what other issue could it be? I made sure all the O-rings were in place when putting the carburetor back on. My other guess would be an air leak between the carb and engine.

The one I pulled from the 17.5hp engine was a Champion RC12YC. The one I pulled from the 21 HP engine was a Champion RC12YZ or XZ or something (sorry didn't write it down). The only difference I could tell between the two was the one from the 21HP engine had a pointy electrode that looked like looked like on a Bosch Platinum or Iridium type plug. Another ever seen this type of plug? It's the same spark plug that came with the mower also around 2009 to 2010. What's the difference between this plug and RC12YC?

I went to O'Relieys for a new spark plug. While he had my engine pulled up on his computer, there was this one particular spark plug that caught my eye. I can't remember the plug but seems like it was made my Champion. This spark plug was $73!!! Why would a spark plug cost that much? And I thought those Autolite plugs for Ford Modular V8 engines at $14.00 a pop X 8 were expensive.

I was in a bit of a rush so I didn't have time to write it down but next time I'm in there I'll write the plug number down to investigate what is so special about it. I tried looking on their website but it's a bit hard to navigate unless your looking for a park for a specific vehicle.

So many questions
1) modern fuels which are nothing like petrol is conductive at cylinder pressure. Either starting fluid is not.
So the tiny amount of fuel that condenses on the plug fouls it and allows the spark to run down the insulator and not jump the gap.
Modern engine run a lot hotter so a lot of modern plugs have no glazing on the insulator or very thin glazing so when you attempt to clean them it makes then more conductive.

2) Spark plugs are very cheap.
When I was young they cost a full hours wages.
The price has not gone up but inflation has caused the actual value to fall.
Think about what you pay for a plug at the shop, 50% to 75% of that price is what they pay the wholesaler for them. and the wholesaler pays 50% to 80% of that price to the distributor who in turn pays 60% to 80% of that to the spark plug maker
And that is with a standard copper core plug
With new high tech plugs there is a lot of exotic materials that go into them and a lot of research that went into them so the cost is higher and this gets amplified 3 to 5 times as it passes through the chain to your hands.

Ether is MUCH easier to ignite than a gasoline/air mixture. Your old plug probably made enough spark to light the either but not the gasoline.

Not trying to be cheap or anything.

It's just quicker to walk over to my bead blast cabinet and hit the plug and it's clean within 30 seconds, blow it off and stick it back in than it is to pick out some clean clothes to dress my 5 year daughter (because she has to go everywhere with me) which is a 10 minute ordeal and drive a mile down to the parts store.

Especially when I'm in the middle of mowing my yard and need a clean spark plug.

I eventually replace spark plugs. Typically I don't replace spark plugs unless they show signs of damage or I am experiencing ignition issues so changing the plug is usually the first thing I do since it's the cheapest and last link in the chain.

I've actually "fouled up" spark plugs to where it would not fire properly when tuning turbocharged engines. I found even slight detonation will cause the plug to glaze over due to higher than normal combustion chamber temperatures. The plugs appeared to be sprayed with clear lacquer and nothing will remove this layer. My guess is the carbon melts and forms a diamond coating. Usually the first sign of a glazed plug is the engine misfires really bad when cold.

I keep a spare set of plugs in my 2 cycle Trabant. I oil fouled a plug the other day getting a bit overzealous with the fuel enrichment valve during start up. The owner's manual says to change the plugs about every 7500 miles but in reality it's more like every 2000 miles.

So keep a 4 or 6 pack on the shelf.
They are cheaper bought that way.
After the mower is hot, pop the bad plug in and usually it will fire in a hot engine.
best of all is to fit a fuel tap.
Stop the engine by starving it.
In the last few revolutions the engine will be very lean and burn off any build up on the spark plug.

Update:

I decided to do a valve adjustment on this engine. I can't remember what the gap was, I probably should have checked. I did this on my other B&S engine after I replaced the blown head gasket so I've done it before. The most time consuming part is scraping the RTV off the valve cover that B&S used instead of using a proper gasket! Adjusting the valves takes about 1 minute. Getting the RTV off the valve cover takes about 15 minutes.

There are several different procedures on this subject but the book says to find TDC and rotate the engine backwards so the piston drops 1/4" BTDC. I just used a Phillips head screwdriver to find TDC and - 1/4" BTDC. This closes both valves at the same time. Some people like to turn the engine over and just one valve then rotate it again until the other valve is closed. I'm not sure why. Then set the gap at .004".

Now the engine starts with no problems.

The question is when the engine hydro-locked due to the stuck float valve could this have messed up the valve lash?

The 14 HP Kohler engine on my Snapper hydro-locked on me 3 times even after I installed a new float valve (1st time) and then a new seat (2nd time) before I finally had to install a fuel shut off valve (3rd time) and it never messed up the valve lash. It was an OHV engine as well.

Is this just something that happens to B&S engines when they hydro-lock?

Actually when you get a hydro lock and it fires up and runs the main thing to go out would be the head gasket at that weak point between the cylinder and push rod chamber........

Back in 1994 or so I got a service bulletin from Briggs stating no more bead blasting spark plugs...... Briggs recommended
a wire wheel on a bench grinder then spraying it off with carb spray.... Their brand carb spray of course LOL.......

Bead blasting was causing scoring in the cylinder walls so they said per the service bulletin........

Yes your plug is the RC12YC..........

Do like Bert says a lot.... Run your engine for a few minutes and shut it off..... Then take the dip stick out and see if smokedy smokes out of the tube......

There is more than one reason for making oil in the crank case... Leaking carb or a bad head gasket.........

Let us know Mon Ami ~!~!

Boudreaux In Eunice La. said:

Actually when you get a hydro lock and it fires up and runs the main thing to go out would be the head gasket at that weak point between the cylinder and push rod chamber........

Back in 1994 or so I got a service bulletin from Briggs stating no more bead blasting spark plugs...... Briggs recommended
a wire wheel on a bench grinder then spraying it off with carb spray.... Their brand carb spray of course LOL.......

Bead blasting was causing scoring in the cylinder walls so they said per the service bulletin........

Yes your plug is the RC12YC..........

Do like Bert says a lot.... Run your engine for a few minutes and shut it off..... Then take the dip stick out and see if smokedy smokes out of the tube......

There is more than one reason for making oil in the crank case... Leaking carb or a bad head gasket.........

Let us know Mon Ami ~!~!

Click to expand...

This float stuck on this mower after it sat over the winter. It seems carbs with the plastic floats are worse about the pins sticking than the older brass floats. It may have just been old fuel.

I was waiting on a new spindle for my other mower so I got this one out.

When the engine hydro-locked, the engine wouldn't even turn over. Initially it was running too rich. I was hoping I could finish my yard then tear the carb apart after I got done. But my dad stopped to talk to me and in the meantime, the engine filled up with gas. When I tried to start the engine, I saw gas fumes coming out the muffler! I was scared the thing might burst into flames!

I mowed with this mower for about 4 or 5 hours yesterday and it did fine. So I don't think the head gasket is blown. It seems to be fine now.

The head gasket that did blow was on my 21 hp Briggs on my other mower.

As far as bead blasting the plugs. I know what your talking about. After I get done bead blasting a plug, I spray the inside and out with a good dose of carburetor cleaner to get any sand beads out of the plug and shake the plug off.

I've never had a problem doing this. I know it sounds cheap and all but has always worked for me.

I'm just curious about how the valves could have gotten out of adjustment on an engine that probably has less than 200 hours on it. I don't know what the valve adjustment intervals are on a Briggs as far as hours goes.

2 different metals getting hot then cooling down, causing expansion and contraction..... Causing valves to be out of adjustment.......

They also wear and the whole engine settles.
The valves get checked on the first service usually between 20 & 50 hours.
After that it is a 200hr service job or 4 years for most engines.