Lawnmower engine runs rough after 30 - 45 minutes

Factual Questions
1

I have a Husqvarna ZTR with a 25 hp Kawasaki engine. It’s about 5 years old but only has about 50 hours on it. The last few times that I’ve used it, it has run fine for a while but after 30 - 45 minutes, it would start to sputter. I have to choke the engine to finish mowing the yard. All the while, the engine continues to run rougher and rougher.

Things that I’ve already tried:

  1. Fresh gas
  2. Changing air filter
  3. Changing fuel filter

Any suggestions would be appreciated.

2

if you have to choke the engine, that tells me air is getting in somewhere in the intake system. look for failed intake gaskets, cracked inlet manifold, and the like.

3

This - and its after it gets ‘hot’ - so be looking for head gasket.

4

Ouch. That is NOT what I wanted to hear.

5

I’m resurrecting my old thread because I got scared of the given answers and have something of an update.

When I went to use my mower today (for the first time this season), it ran fine for a few minutes but I had to choke it much sooner than before. Probably more like 5 minutes this time. I guessing/hoping that it’s some kind of fuel flow issue instead of manifold issue.

The fuel filter that I replaced the old one with seems to go “dry” quickly. As in, there’s no fuel in the filter housing. It will fill up again eventually and run fine for a little while. I removed it and blew on it and I had no trouble blowing gas out of it. I tried loosening my filler cap in case there was something wrong there but it didn’t seem to help.

Any other ideas as to what I could check fuel flow wise? I could easily replace the filter again but my guess is that that’s not the problem but just a symptom.

Thanks.

6

I think the previous answers give you what you need to know. Somewhere in the air/fuel intake system there’s a leak or malfunctioning choke. I’m no small engine expert but this sounds like some disassembly is required to find this. I’d just find a good small engine guy to work it out at this point. YMMV

7

I wish that it were that easy. My mower is too big to fit on my trailer and I live WAY out in the sticks and there isn’t a good small engine guy within 50 miles of me.

8

if it’s a diaphragm carburetor, ethanol could be degrading the diaphragm and the carb can no longer pump fuel.

9

Check for a restriction between the gas tank and the inlet hose to the filter. Perhaps there’s a hose that’s narrowed inside, or one so soft it collapses during use, or a big chunk of debris in the way.

10

Thanks. This ended up being the issue.

I disconnected the hose and blew on it and it immediately started draining MUCH faster. I’m not sure what I can do long term but I’ve had this mower for 5 or 6 years and this fall was the first time I’d had any trouble with it. Just one of the perils of living in Dust Bowl country I suppose.

Thanks again for all of the suggestions.