# Lawnmower engine runs rough after 30 - 45 minutes
**URL:** https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110
**Category:** Factual Questions
**Created:** [October 10, 2015, 2:07am UTC](https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110 "2015-10-10T02:07:48Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)
#### Post date: [October 10, 2015, 2:07am UTC](https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110/1 "2015-10-10T02:07:48Z")
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.
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### Author:  [@jz78817](https://boards.straightdope.com/u/jz78817)
#### Post date: [October 10, 2015, 2:10am UTC](https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110/2 "2015-10-10T02:10:17Z")
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.
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### Author:  [@simster](https://boards.straightdope.com/u/simster)
#### Post date: [October 10, 2015, 2:10am UTC](https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110/3 "2015-10-10T02:10:58Z")
> [@jz78817](#):
>
> 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.
This - and its after it gets ‘hot’ - so be looking for head gasket.
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### Author:  [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)
#### Post date: [October 10, 2015, 2:22am UTC](https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110/4 "2015-10-10T02:22:40Z")
Ouch. That is NOT what I wanted to hear.
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### Author:  [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)
#### Post date: [April 8, 2016, 3:16pm UTC](https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110/5 "2016-04-08T15:16:49Z")
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.
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### Author:  [@TriPolar](https://boards.straightdope.com/u/TriPolar)
#### Post date: [April 8, 2016, 3:29pm UTC](https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110/6 "2016-04-08T15:29:03Z")
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
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### Author:  [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)
#### Post date: [April 8, 2016, 3:48pm UTC](https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110/7 "2016-04-08T15:48:29Z")
> [@TriPolar](#):
>
> 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
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.
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### Author:  [@jz78817](https://boards.straightdope.com/u/jz78817)
#### Post date: [April 8, 2016, 3:53pm UTC](https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110/8 "2016-04-08T15:53:42Z")
if it’s a diaphragm carburetor, ethanol could be degrading the diaphragm and the carb can no longer pump fuel.
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### Author:  [@Gary\_T](https://boards.straightdope.com/u/Gary_T)
#### Post date: [April 8, 2016, 3:54pm UTC](https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110/9 "2016-04-08T15:54:41Z")
> [@Nars\_Glinley](#):
>
> 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.
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.
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### Author:  [@Nars\_Glinley](https://boards.straightdope.com/u/Nars_Glinley)
#### Post date: [April 8, 2016, 11:56pm UTC](https://boards.straightdope.com/t/lawnmower-engine-runs-rough-after-30-45-minutes/734110/10 "2016-04-08T23:56:50Z")
> [@Gary\_T](#):
>
> 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.
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.