16HP Horizontal Shaft Vanguard Losing Power Sporadically

I have a Woods 5160 mower with a 16HP B&S Vanguard (303447-1454) that is losing power sporadically. Most of the time it runs great. On occasion it loses power and will barely propel the mower with the blade running. When it's in this state, I can often sit with it idling and hear it suddenly start running better and all is fine...until it happens again. It acts like there is a sticking valve, but I had that earlier in the year and replaced one of the heads. The valves seem to be moving freely and they are adjusted to .005.

This season I have changed all fuel lines, fuel filter, fuel pickup tube, air filter and spark plugs. I've tested the fuel solenoid and it appears to be working. I've emptied the fuel tank and cleaned it out. I've checked the fuel cap and the vent doesn't appear to be clogged. I noticed that the idle screw on the carburetor has no effect on the speed of the engine so I'm thinking the carburetor needs to be rebuilt or replaced. Any thoughts from the pros? Any further information needed to form an opinion? Thanks in advance for any help.

 

It's probably losing spark on one cylinder. It could be other things, but this is probably thee most common. Have a spark tester handy and check each cylinder when it happens, or put an inline tester in the line and you can watch it when it happens to see which side loses spark when it happens, or if neither do.

 

Thanks for the reply. I picked up an inline spark tester tonight. If I find that it is losing ignition on once side, what would the likely culprit be? How would I test/troubleshoot? Thanks again.

 

If that's what's happening, then the likely culprit would be a coil going bad, but could also be a bad kill wire. There is a diode in the kill wire that sometimes causes this problem.

 

Update to my question. I used the mower and had the same problem. When the problem started, I pulled one sparkplug wire and the engine wouldn't start. I replaced that wire and uplled the other and the engine would start and sounded like it was running fine. I pulled into the barn and stuck an inline tester on the side that didn't seem to be running. The light in the tester looked very faint. Ordered a new coild and kill wire harness. Just replaced both this morning and mowed the normal amount and mowed some additional to try to see if I could get the problem to repeat. Everything worked fine and the problem didn't appear again. I think this issue is fixed. Between this and the replacing one head earlier in the year, I hope I don't have anymore issues this year.

Thanks again for your responses and advice.

 

Good, sounds like you've got it licked. Thanks for the update!