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I've got a Simplicity Champion ZTR with B&S 20 HP Vanguard 35877-0280-E1 engine. Residential use only, 10 years old, 500 hours. Last summer it was running rough and the dealer overhauled the carburetor. Still ran rough, burning gas faster than it used to. In March the dealer performed "winter maintenance," replacing all filters, plugs, fluids, etc. Brought it home and was puffing black smoke out the exhaust and still running rough, sounding like it wasn't getting up to full power at full throttle. It deteriorated over 4 cuttings (about 2 hours per week cutting) and ran rough/inconsistently at idle and full throttle.

Dealer tech says ignition coils. I'm tired of spending $400 every time I take it in, so I thought I'd tackle this myself. A co-worker of mine has done much of this kind of work himself and said to sand the face of the coils to remove the rust, and also the flywheel. Then set the gap between the magnetos and flywheel to about the thickness of a business card and try it again. Before I removed the magnetos, it looked like the gap was pretty narrow to begin with.

What I'm looking for here, as the title suggests, is whether to bother with the sanding of the flywheel and magnetos or just order the parts. I suppose cleaning up the flywheel is a good idea even if I replace the magnetos. Do I need to be mindful of turning the flywheel as a run my little detail sander? Is there an alignment indicator for timing on this engine?

First time doing anything more than changing plugs and scraping crud out of the deck, so I'm open to all guidance.

This may sound like a dumb question. Are we sure that the dealer that is doing the service is using the correct air filter. Briggs has two air filters that are almost identical to each other, but slightly different height, and different filtering media. If you install the wrong air filter it will do what your mower is doing within a few hours of replacing the air filter.

make sure you have the 692519 air filter and not the 694018. The other thing to check is make sure it has the RC14YC or equivalent spark plugs, and not the RC12YC, because they will cause the same thing. Rich running. no power.

smollen , IL Eng good advice. Perhaps what he is saying is that the wrong filter is too restrictive, acting like a choke, producing black (rich) smoke. Fully understand your reluctance at shotgun approach. If the engine is not dying or missing I would hold off buying those coils.

Had a Cub Cadet a few years ago come in blowing black smoke, Air filter was replaced about a week before problem started. Could remove air cleaner cover and engine would clear up immediately. Briggs has a service bullletin about this on the Vanguard 35 and 38 series engines. Customer had installed the 394018 filter instead of the 692519 filter. The two filter are almost the same size, and will both fit the engine. But the 394018 restricts air flow. The 692519 looks like it has less filter media than the 394018.

Had a MTD come in a few years back also. Customer had just replaced spark plugs the day before. Blowing black smoke and no power. Found RC12YC plug in engine, Vanguard calls for RC14YC. Replaced with correct plug and engine cleared up immediately. No hot enough plug.

Sounds like he needs to look for a new dealer.

The plug pns relate to how much insulator tip is exposed to the combustion heat (as IL ENG states). The more, the "hotter" the plug is and more it will burn off deposits . (Do I have that right?)

The Vanguards had a problem with the coils getting rusted up, but where you needed to sand is where they mounted/grounded on the block, sanding the flywheel is pretty much a waste of time.

Clean up the coils and set their gap, then if the spark looks strong and consistent, look at your fuel system.

Well, I should have been checking the forum replies more frequently. I'll try to address the questions and suggestions you've all provided as much as I can based on the little time I've been able to work on this.

I checked the air filter - the part number is correct.

I tried co-worker's suggestion about sanding. The left one actually felt magnetized as I put it back in place. The right one did not seem as strongly attracted to the block. That was also before I read Fish's suggestion that the mounting points are where the sanding should be done. I'll try that.

I sanded the laminated plates facing the flywheel (and the flywheel itself - hadn't read the remark about that being a waste of time, but my Dremel made quick work of it). I then had to jump start the machine because of the problem with the charging system failing to refresh the battery. Let it sit on the jumper cables for a few minutes connected to my truck, then fired up with much smoking and sputtering. I pulled the throttle down to idle and it smoothed out and quit smoking. I left it running at idle for several minutes while I removed the jumper cables and put the track away. Tried going back to full throttle at a usual speed and went right back to smoke and sputter.

If I increased throttle slowly I was able to go from idle to about 2/3 before it started getting rough again. Backed off just a little and was able to drive the mower off the trailer it was sitting on in anticipation of a delivery to a different repair shop and parked it in the garage. Put the battery charger on for now.

After reading the other posts about spark plugs, I went back to last summer's repair ticket which showed RC12YC instead of 14. The March ticket says 14, but I don't trust that. I'll be pulling those plugs tomorrow night and confirming part numbers. I don't have a spark plug tester yet, but I may borrow or buy one to check coil performance after the plug part number is confirmed and cleaning the coil mounting areas.

Anything else I should do at this point?

Sounds like you have many troubles, including a blown head gasket. Or who knows, as you are all over the place without really addressing
any suggestion yet.

Yes, buffing the flywheel is quite silly, as the rust on a flywheel doesn't give a chit about some light rust.....

But the ignition coils need a good clean ground to function properly, and that is where the vanguards need looked at....

But one needs to consider the OHV/head gasket scenario. Also, your description of events suggest it may be a simple fuel problem......

But to diagnose here online, well, we need your help.....

Eureka! Many thanks to everyone who contributed troubleshooting tips and suggested other possible causes. And especially thanks to Fish for the obvious comment "he needs another dealer" which turned out to be the real cause of this entire rabbit hole. Root cause = CHOKE CABLE FAILURE!!! It had nothing to do with magneto or spark.

To recap:

1. Checked the spark plugs - last summer's service ticket showed the WRONG PLUG as warned by ILENGINE. Most recent service ticket and an actual extraction and cleaning of the current plugs confirmed the correct ones had been installed this time. No telling how much damage was done overall by those wrong plugs being in there for half the season! AND one of the plugs had NO GAP. Looked like someone had smashed the end down onto the plug. The other plug was almost the right gap.

2. Cleaned the mounting points for the magnetos.

3. Testing showed no real difference in performance. Idled a little smoother, but under load it went back to belching black smoke, chugging, sputtering, you name it.

4. Just before ordering new magnetos online I went to a local lawn mower dealer, not Simplicity, but a Toro, Deere, Stihl shop in Washington, IL, Wieland's Lawn Mower Hospital. Described the problem to the young man at the counter, Cody, and he immediately said it sounds more like a problem with choke or throttle controls. He diagrammed what I should look for in the carburetor area, pointing out butterfly position, etc.

5. Opened up the breather area on the engine, looking at the movement when the choke cable was activated. IT NEVER WENT TO FULL OPEN!!! I disconnected the cable from the operator's control and moved it using just the engine block control. I was able to move it to full open. Started back up and it runs great.

So the dealer who wanted to put $90 worth of parts and probably $150 in labor on my machine with no resolution to the problem is going to be lucky to get partial payment for the crappy work they did over the winter and the damage caused by putting the wrong plugs in last summer. Wieland's, while not a Simplicity dealer, will likely get more of my small engine business just because they demonstrated some brains. I also will keep coming to LawnMowerForum.com for more advice and guidance. Thanks everyone for your help.

I have found that service dealers usually are parts changers !
Good techs can spot the problem and fix with minimum cost . ( find them during conversation )
Have not yet found tech that can identify/fix my mantis -no spark-situation ,all new parts and following all the good suggestions herein. Frustrating as I have done many of these before .
Hoping to find help !!!
I am -HVAC tech engineer 70 yrs experience .

Let ask here did you have a thread here that I can go thru to what actually got done in reference to the Mantis?

And you right about dealers having what now a days to be just part changers. Many us older experience techs just can't get because the owners are afraid of us. That what I ran into back in 2006 when I had 16 yrs of experience working on equipment. This actually some the potential employers said that I had too much experience.

I spent three year job hunting before I finally decide to start my own business then I young punks coming telling me they knew everything. They all fail simple troubleshooting of problems in my shop. Most didn't have the faintest idea how troubleshoot wiring problems yet alone rebuild a carburetor or a deck spindle.

ILENGINE said:

This may sound like a dumb question. Are we sure that the dealer that is doing the service is using the correct air filter. Briggs has two air filters that are almost identical to each other, but slightly different height, and different filtering media. If you install the wrong air filter it will do what your mower is doing within a few hours of replacing the air filter.

make sure you have the 692519 air filter and not the 694018. The other thing to check is make sure it has the RC14YC or equivalent spark plugs, and not the RC12YC, because they will cause the same thing. Rich running. no power.

Click to expand...

I thought the vanguards call for the RC12YC plug. I have put well over a hundred of them in with no issues.

I kinda by internal SKUs lookup. And the 491055S supersedes to 84007216 which listed as RC12YC.

Hammermechanicman said:

I thought the vanguards call for the RC12YC plug. I have put well over a hundred of them in with no issues.

Click to expand...

Current recommendation is the RC12YC with the RC14YC being listed as a platinum long life aka hot plug. Years ago the Champion spark plug catalog listed the RC14YC for the Vanguard engines. Had more than one Vanguard that had brand new less than 10 minutes run time on RC12YC blowing black smoke and heavy carbon fouled plugs, that would immediately run straight when switched to the RC14YC.