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Trying to help out my neighbor with her mod 1050 Cub Cadet problem.
sv720 engine with 500 hrs. Starts ok, new battery last year, shows 13.7 v with engine running so I think the charging system is good.
When she mows it runs fine for about 30-45 minutes then starts misfiring, almost sounds like a rich fuel condition but no black smoke.
I told her next time it does it, shut the thing down without touching the throttle or anything. I looked at the plugs and they looked normal. I replaced them with new anyway and the problem is still there.
Checked fuel system including breather on filler cap - couldn't see anything wrong. Air cleaner good.
I suspect it is an ignition breakdown rather than fuel because it runs fine for awhile.
I pulled off the engine cowl. The cylinder fins etc were clean - no obstructions or anything to cause overheat.
Compression is 180 both cylinders.
At this point I am looking at the ignition modules (my first thought), but @$70 ea. that an expensive guess.
I don't have any special diagnostic tools, just a multimeter and the usual stuff.
Is it time to haul it to the shop?

:welcome:

A $ 10 in line plug tester i a lot cheaper than replacing a perfectly good $ 80 module.
Fit it where it can be seen from tne operators seat.
When the engine starts playing uo look at the tester.
If the tester contines to flash as the engine is missing then she has a fuel problem, if the flashes dreak down in sync with the engine then it is an electrical problem.
Let us know what happens and we will take you from there.
Also heed the previous thread and send the number.

Sound like a tight valve, check your valve adjustment .004/.006 That engine has mechanical lifters.

PS-SV720-0010, ser# 3532318163
I woke up this morning thinking of using the spark plug checker when the engine is misfiring but wanted a cold engine for valve clearance check.
Results one side:
in: .005
ex: .018

Other side:
in: .005
ex: .020

I can hear leakage when wrenching the crank around. It seems like the only way the exhaust valves could gain clearance would be carbon buildup.
The leakage sounds bad enough that I think a static compression test would fail.
Current condition seems that it would result in reduced performance under load generally, not just when it's hot.
I'll try it with adjusted valves and then the spark tester if necessary.

hakelly said:

PS-SV720-0010, ser# 3532318163
I woke up this morning thinking of using the spark plug checker when the engine is misfiring but wanted a cold engine for valve clearance check.
Results one side:
in: .005
ex: .018

Other side:
in: .005
ex: .020

I can hear leakage when wrenching the crank around. It seems like the only way the exhaust valves could gain clearance would be carbon buildup.
The leakage sounds bad enough that I think a static compression test would fail.
Current condition seems that it would result in reduced performance under load generally, not just when it's hot.
I'll try it with adjusted valves and then the spark tester if necessary.

Click to expand...

inlets are fine . exhausts are way to big
Exhaust valvle springs are stronger than inlets so they push harder on the cam , cam followers and the pushrod ends.
Slip the pushrods out and check they are strait and for wear on the ends.
Excessive clearence means the valves open latter & close earlier so choke the engine when it is on full throttle .

Problem solved. I adjusted the valves and cut grass for 1 1/2 hrs. Everything running fine and just when I thought it was fixed, it sputtered and died. Since I was on the scene for this one, it was apparent there was fuel starvation at the tank.
I removed the tank and poured out some small wads of grass clippings (which was the real culprit) and an old plastic gas can spout with other fractured pieces.
I confronted the perp about this crime and she broke down and confessed. CSI Lawn Mower edition.
There was a small enough amount of clippings that they came loose and floated around, especially after refuelling, and over time got to the tank outlet and clogged it, but didn't stay there after shutdown.
So many posts on here about trash in tank, it should have raised a red flag for me.
With that great big filler hole - which I thought was a real improvement originally - well it is if you use care in refuelling, but there is no filter on a hose such as on chainsaws that you can pull out and inspect, and no way to inspect except dumping fuel and pulling the tank.
Thanks to you guys for taking the time to help me sort this out. I really appreciate it.

Gees I like that idea CSI MOWER. You might like to take that up with BDO.
Could be a money maker.