Mower loses RPM's like a switch was flipped

[Mr. G]

I'll see if I can a place to do the ultrasonic cleaning, and compare that to the cost of a new one.
At this point, are we pretty sure it's the carb? Or is there anything else I might be able to check before I involve a professional?
Thanks

 

[Mr. G]

I got the carb back from the ultrasonic cleaning and rebuild, $102 total. I still have the same exact problem. It's not the carb, unless the cleaning missed something. The shop said I could bring it back to have it cleaned again, but it's so clean, only 200 hours, I don't think this is the problem.
I got a spark tester and when the engine started to show it's *** I caught it on about the third time; the right side spark plug wire had no spark. While I was watching the tester, in about 1 second the spark reappeared, and the engine was singing at full song.
Did I find the problem? And what next?
Any help is appreciated.

 

[Mr. G]

I took the ignition module off of the right side, the side with no spark, last night. The shop said they've got the ignition module for $56. I'll try to pick up the new one on Monday.
Oh yeah, that "other hole" I was talking about was on the plastic "breather" that sits on top of the carb and holds the air filter. I believe there is supposed to be two holes there.
I'll update after I get the new ignition module installed.
Am I heading in the right direction?

 

[Mr. G]

I'm in the eastern time zone and it's 11:30 here, not 3:30; where is the server I wonder?

 

[Rivets]

Before you pick up a new coil, try removing the kill wire on the coil, ignition module, set the air gap at .010 and see if you have consistent spray. You can do this with the should off. If the engine runs smooth, you may have a kill wire short. Don't run it to long will out the should, as it is a main part of the coll system.

 

[Mr. G]

Thanks for the reply, however I'm still a novice on engine work. I think I can figure out which wire is the kill wire, but I don't know what you mean by set the air gap at .010 and check for consistent spray. I'm guessing the air gap of the plug? and consistent spray somewhere in the carb?
What is a should and a coll system? I'm guessing the shroud maybe, the plastic around the engine. I don't see any way to take apart the ignition module. And coil system or cooling system?
I just found out the shop would need to order the ignition module and they are $101. I'd like to try your method first, but really sure what to look for.

 

[Rivets]

If you look at the electrical diagram part (I) is the ignition module (coil). The air gap I am talking about is between the legs on this coil and the magnets on the flywheel. Read pages 67-68 of the manual I posted.

 

[Mr. G]

OK, I understand the magnet and coil part now. Thank You! The manual says the gap should be 0.30mm or 0.012in. between the magnet and the ignition module. I'll check the gap with some feelers or something. I'll will remove the kill wire on the coil, check the gap, and crank it up but I'm still not sure where to look for the consistent spray. I guess I would notice the by the engine sound.
Usually the mower doesn't have any problems until about a 10 minute warm up. I guess I should I should get it warm first of all, then do the other stuff?
I took the coil over to the shop; they said they tested it and said it was bad. This is the first time I've used this shop, not sure if I can trust them. I didn't buy a new one yet. Can you test a coil in a shop? it really wouldn't be the same as being in the mower's conditions, heat...

 

[Mr. G]

After looking at the mounts for the ignition modules, they look like they cannot be moved/adjusted like the manual says. I guess that is for a different model. There is no way for them to slide. It bolts solid to the cooling fins with two bolts. I see the magnet spins past both ignition modules but there is no way to adjust the modules. Does the magnet adjust?

 

[Rivets]

The coil legs have slots, loosen the two bolts, 1/4" nut driver works best, pull the coil away from the flywheel and tighten the screws. There gap at this point is less than .050. Turn the flywheel until the magnets lineup with the coil legs.insert feeler Gage, I use .010" on all engines. Loosen screws and the leg should draw tight to the flywheel, you need to do both legs at the same time. Retighten the screws and you are done. Magnets on the flywheel cannot be changed or moved. Hope this makes sense. Today's coils can be tested with a specialized expense tester, which many shops do not have. I test them by setting the coil, removing the kill wire, and spinning the flywheel while looking for spark. No spark, bad coil. I do not have the bench tester to test off the engine. Hope this helps.