B&S 18HP model 31D777 problem

15 years ago

Engine: B&S 18HP Model 31D777/type 0233E1/code 0304177E about 8 years old on a TroyBilt 42" riding lawn tractor

A few weeks ago, I was mowing the side of a slope when the engine coughed and exhausted a big cloud of dark gray/black smoke. During this episode it backfired a couple of times. It sputtered until I got it on level ground where it seemed to smooth out.

Then a week or so ago, it did the same thing, except this time it died and I was unable to start it. I replaced the plug which was VERY fouled (and the air filter (no oil or gas evident on the filter), and the engine started and ran normally until yesterday.

Then it sputtered, backfired and exhauted a small cloud of gray smoke, and quit running. I was able to get it started and it ran until I got it back to the garden shed. I turned it off and have been unable to get it to start again. I have changed the oil and filter, spark plug and air filter. I took the plug out and it appears to have a little bit of black stuff on it (not nearly as bad as the previous episode).

THe engine will turn over, and the PTO, brake and seat safety interface switches seem to be working because the engine won't turn over if the PTO is engaged or the brake pedal is not depressed or their is no load on the seat.

I must confess that I'm pretty sure I overfilled the oil level a year or so ago. My bad. The oil seemed to become thinned and very black quickly, even after I changed the oil, so I'm guessing that there's some fuel leakage into the oil compartment.

There is a black hose that connects to the back of the carburator (the PCV hose?) that was off, but when I reattached it the engine still wouldn't start.

I'm presently alone so it's hard to check for a spark in the plug. The plug wire seems to fit loosely on the plug but the fitting inside the plug wire seems OK (it's round with no way to "tighten" it apparent, to me at least.

I'd appreciate any advice on what to do now. If I can repair the engine at a "reasonable" cost (less that the cost of a new engine) I'll try to do that. If not, then...

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Comments (11)

James Hogan
Original Author
15 years ago
Have now checked the plug and am getting spark. Drained and removed the fuel tank, thoroughly cleaned it, dried it and blew it out. Installed new fuel line and filter. Removed valve cover and the valves , rocker arms and push rods seem ok. Nothing broken. This engine doesn't have a fuel pump--gravity feed.

There was a lot of built-up gunk in the spark plug that was so fouled. Mostly carbon and what appears to be black, wet substance.

But it still won't start.
mownie
15 years ago
Buy a can of spray carburetor cleaner. With the air filter cover off, spray about a one or two second burst of the carb cleaner into the carburetor throat. Then try to start the engine.
If the engine starts and runs for about 2 seconds each time you spray the cleaner into the carb throat....your no start issue is due to no fuel delivery from the carb to the intake.

If, however...the carb cleaner does not provoke the engine to run (for a couple seconds) that means the problem lies elsewhere.

Bear in mind, the mere presence of a spark does not mean the spark is happening at the proper time. It is possible that the first episode of trouble, resulting in some "back firing" may have partially sheared the flywheel key, which would put the ignition spark timing to something other than the proper time.
But don't go yanking the flywheel off yet.
Let's see how it does on the alternate fuel (carb cleaner) first. Then we'll go from there to a next step.
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James Hogan
Original Author
15 years ago
Tried the carb cleaner. Engine wouldn't fire at all.
James Hogan
Original Author
15 years ago
Adjusted valves to .004 (intake and exhaust). Gap between coil and magnet is about .013. Still eon't start.
James Hogan
Original Author
15 years ago
Have gone back and rechecked everything. Now there's no spark. Is it possible that the coil is going bad and there's only an intermittent spark? If so, is the solution to replace the coil? Any suggestion where to buy parts for this engine?
tomplum
15 years ago
Remove the small wire from the coil and if you have no spark, buy a new coil. If you do, look towards the safety switch side of the system. When I read the 1st post, I was questioning whether the tabs on the seat switch were making intermittent contact as people like to sit way on the edge of the seat on slopes. be sure to check the flywheel key as Mownie suggested.
James Hogan
Original Author
15 years ago
I presume you mean the kill switch wire? I removed it, gave the carburetor a blast of carb cleaner but still no sign of ignition. Will look for a new coil tomorrow.

I'm not sure how to get into the flywheel and the shear key. Is there a link here that describes how to do that (without breaking something)? I had found one of Walt5's links that had a bunch of technical publication's but now I can't find it or the bookmark I made.
walt2002
15 years ago
Well here I am. Address below, put in proper format and remind me PLUS I am experiencing a bunch of computer trouble so don't think I am ignoring you.

Walt Conner
wconner5 at frontier dot com
tomplum
15 years ago
You can remove the bolt and visually inspect that the key and slot are aligned. You could wait and see what you have when you replace the coil as a sheared key will not eliminate the spark.
James Hogan
Original Author
15 years ago
Installed new coil and adjusted to instructions that came with it (set gap to .010). Inspected flywheel key. It doesn't appear to be sheared or even dented. That is, the key is in the key seat and doesn't appear to be misaligned at all. Installed new spark plug. Tried to start engine and it tried to start once (with the carb cleaner.) Then it turned over several more times then backfired out of the exhaust, I think.

Tried starting with the kill switch wire on and off. Tried starting the engine several more times, but then I got a backfire through the carburetor.

To be clear here--the engine tried to start once (on carb cleaner)but hasn't been provoked to start again. But did get two backfires so there must be a spark getting to the plug.

Any ideas?
James Hogan
Original Author
15 years ago
I am very happy to report that the problem was a bad coil. I reset the coil after the previous post, turned on the key and the engine started and now it's running like new.

I want to thank Mownie, tomplum and Walt2002 for their assistance. I saved myself some money, and learned something in the in the process.

Now to get the lawn mowed before the big storm gets here tonight. Thanks again.