Problem with Briggs 25hp ELS

17 years ago

I have a Deere LA155c with a 25hp Briggs 25hp ELS Twin. Mower had 67 hours over two seasons when the problems started. I was mowing the yard and the engine started surging. Before I could get it back to the garage, it died. I looked it over and noticed the fuel filter was empty. I disconnected the line between tfilter and pump, and teh filter immediately filled. I put the hose back on and the mower ran normally for 15-20 minutes, then repeated. I replaced the filter and it did the same. Took it to the dealer and they replaced the carb saying it must have trash in it. Brought it home, mowed the lawn once, seemed ok. Mowed teh next week, got half way through my 1 acre yard and it started what I would guess is a lean miss with an occasional popping. A little choke would help, but not "fix". Happens worse at half throttle without the blades on. Took it back to the dealer. They replaced the carb again. Brought it home. Mowed last week, all was ok until I was driving back to the shed. Sounded like it was popping/missing again. Got it out tonight and half way through the yard and its back to a bad "lean" miss. Took it back to the shed. Sitting still, if I go to half throttle, it has a muffled popping/miss. If I go to half choke, engine speed increases very noticably and it smooths out quite a bit.

I have checked from the filter to the tank and the line is clear. The fuel filter has had ~5 gallons put through it since replacement. I have also made sure the fuel is fresh and from a clean gas container. Seems the problem is fuel related, but the only part besides the lines not replaced is the pump. The tube from the valve cover to the carb is visibly cracked, but i can't tell that there is any leakage going on. I pulled the line from the pump to the carb and turned the motor over, fuel pulsed out. I'm calling the dealer again tomorrow, but am trying to get an idea what is going on. After 2 new crabs in 3 weeks, I think we can rule out a carb issue? Any suggestions? Motor now has 71 hours. This is nuts.

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Comments (9)

jasonnb
Original Author
17 years ago
I will add, the engine doesn't use oil and starts just as easy as it did when new.
jasonnb
Original Author
17 years ago
I checked the fuel caps for clogs as well.
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tomplum
17 years ago
I believe you are referring to the pulse line between the valve cover and fuel pump. That needs to be secure and leak free. What little bit of vacuum pulse comes through there runs your fuel pump. Replacing the carb twice seems strange to me.Have they been having problems with them? Hopefully they have enough sense to ensure that the fuel system is clean to start with. I wouldn't rule out the loose valve guide issue, though one would think it would have tossed a push rod in that 6 hours of use.
mownie
17 years ago
Has anyone checked the cooling shroud sheet metal for mice nests or food caches? 15-20 minutes run time might be about right for the engine to heat up and develop a very lean mix condition. The fact that applying a bit of choke improves it somewhat supports the idea that the mixture is too lean. If the pulse tube indeed has some kind of crack in it, the fuel pump will perform less effectively and that too could aggravate the lean condition.
jasonnb
Original Author
17 years ago
I haven't checked that shroud, but will. I have asked the dealer twice about replacing the tube, but it has yet to be done.

They didn't say anything about known carb issues, just saying maybe there was trash they missed. The filter is clean and new, how much trash could be between teh filter and the carb by now? I'm thinking about adjusting the valves before I take it back to them just to see how loose they are.

It seems to run fine until it warms up.

I'ma decent shadetree mechanic for outboards and cars, just hate to tinker with a $1000 mower motor....
walt2002
17 years ago
IF ALL ELSE FAILS on these engines, try disconnecting the "Kill" wires from BOTH coils and see if this makes any difference.

Walt Conner
jasonnb
Original Author
17 years ago
Just a follow up. After going ahead and swapping the fuel pump, filter, and pulse line (cracked, but not too bad yet) and getting no where, I decided to pull the engine shroud myself. Never overlook the obvious...... I found that the dealer had apparently left off the PCV? hose between the crankcase and the intake plenum. Put it back on and mowed about half an acre and quite a bit of just driving around. Never a whimper, miss, or sneeze.
swamadcat
17 years ago
I just don't see how a pvc line left off would do anyting to fix your problem. I could see that if it was stuck closed. Maybe you freed it up
walt2002
17 years ago
I don't see any connection here either. I think someone got the vacuum line for the fuel pump and the crankcase breather vent lines reversed.

Walt Conner