Mower issues..B&S 450 classic engine

Werewolf

Werewolf

Werewolf

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17 Oct 2002
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Panting like a fiend
Hi

Our trusty McCulloch mower seems to be playing up.

We changed the oil on it a few weeks ago, carefully checking the levels, it cut the lawn fine once, then did another 3/4 of it before it started running very rough.

Checking the sparkplug showed it was dirty (probably not surprising, it's 7 years old), so we fitted a direct replacement.

That didn't cure it, the mower still starts up fine, runs normally for about 15-30 seconds then starts running rough.
Checking the spark plug shows it's getting very dirty fast.

The oil level seems to be ok according to the dip stick (and the measure).

The exhaust smells like it's burning rich, or burning oil (it seems to be darker than before).

I'm not sure what to check next as we also replaced the air filter, but there doesn't appear to be many other user servicable parts on the engine, and it's not really worth us potentially spending 25-50 to get someone to look at it, given it's 7 years old and only cost about £150 when new.

The engine code is
09t502-2229
 
How old in the petrol in it, I was told by a guy who services our mowers at work that the petrol doesn't keep well now so he recommends running it to empty before the winter.

Does it have a fuel filter? Its possibly contaminated if it does, could be causing the mower to run lean after the initial fuel is pulled through its then causing a restriction
 
Suspect it will be the carb diaphragm needs to be replaced if the plug is coking up quickly. Had the same on my Briggs engined mower last year, and was simple enough job following YouTube guide.

Hardest part was finding correct part number to get replacement (which was about £5 iirc including new gasket).

Edit:
 
Cheers for the replies.

The petrol is fairly new (this spring I think), I've ordered the parts Armageus and that video makes what I was expecting to be a really hard job look easy :)

Hopefully I'll be able to report a success next week, either that or my ability to touch type will be degraded by the loss of fingers whilst fiddling with the mower :p
 
I had very similar problems with my old B&S mower. I bought the a service kit from Ebay which had the air filter, spark plug, oil and diaphragm. It was about a 15min job to swap them all and it ran perfectly after that.. Just a shame the metal around the blade corroded away so I got rid of it as the engine was still working fine.
 
I also had the diaphragm issue on one of these engines a few years ago. Think the genuine gasket and diaphragm was 4 quid on eBay and it took about 20 mins to do. The old one had a tear in it.
 
You guys are stars :)
We changed the diaphragm last night in the garage i it took about 15 minutes, and seems to be working as good as new.
The engine started first pull and is running lovely and smoothly, with a clearer exhaust.

The old diaphragm was very sloppy, unlike the new one which was quite taut on the bit that moves.

The only thing I did note was that the diaphragm wasn't 100% identical to the old one, it looks like the new one is designed to work on two models of carb.
 
Next up.

Sorting out the chainsaw...
It looks like the chain brake is in need of a replacement part or something tightening up. I foresee an expedition to reach the fabled drawer of many manuals in the wilderness that is the Garage (I really need to tidy up in there), followed by a trip to A&E.
 
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