OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Reel Lawn Mowers, Atco & Villiers etc. Scott Bonnar 45 Randomly Stalls

Hi, i am new to this forum, have been following it for ages and have now joined as a member.

I have a Scott Bonnar 45 that starts up fine but after a few minutes of mowing, its seems to start running rough and stalls until it is not running anymore.
It starts up ok not long after but will do the same again.

I have down the following in terms of maintenance:
- removed carby and replaced gasket between the fuel tank and the carby.
- replaced the diaphragm
- replaced the spark plug
- checked the air filter, it is not brand new but still look relatively clean
- drained and replaced with fresh fuel
- replaced the engine oil
- sprayed carby cleaner into the carby whilst running to try and clean the internals out
- the choke seems to correctly operate

I have tried adjusting the mixture needle to a point where i think i can hear a slight difference with its tune but still stalls moments later when i engage clutch.

This has been puzzling me for a while and keen for any advice?

The below details are on the actual mower frame:
The model Number is: 45058
The Serial Number is: 371092
Its a Briggs and Stratton Engine

The below details are on the actual engine:
Model Number: 80202
Type: 2324 01
Code: 90100303


Thanks

Attached a photo of the mower

Hi Miloboy welcome here from wherever Mount Louisa is. What I would do is remove the air filter, start the motor, rev it up by moving the governor arm and jam your thumb down on the top of the carby inlet, hold it there till the motor nearly stops then release your thumb, allow the motor to come up to revs again and then repeat the process. Do this maybe half a dozen times and see if that solves the problem, it often does,but sucking a bit of rubbish/gunk inside the carby. Worth a try and nothing to loose.

Thanks i will give this a try. Is there any way i can thoroughly clear out the carby if i pull it back off completely to flush?

This sounds like a classic case of fuel starvation.

I'd say it's got a blockage in the fuel supply tube that picks up the fuel from the tank up into the carby or as Norm suggests a bit of gunk that's being pulled up and gradually block the supply. After it stops and sits for a while the blockage reseeds downwards and again the process is repeated after it's been restarted.

I'd follow Norm's advice and see if that solves the issue, if not then its a carby off and blown out all holes with compressed air.

Cheers,
BB.

Thanks heaps BB will certainly give it a go.

Tried the suggestion from NormK with revving and temporarily blocking the carby inlet and i was able to mow without any dramas. Will see how i go again next time i mow as this seems too good to be true

Glad it helped Miloboy an old trick I learned over 50 years ago.

G'day all
Yep, always great advise from the pros.

My suggestion - long term - is to replace the carby diaphragm.
You have a pulsa-jet - and diaphragm condition is critical.
They deteriorate with age.

Apart from tube blockage, air leaks, and fuel quality, the diaphragm
is the critical link in fuel starvation. The pulsa-jets had a small
fuel pump to lift fuel from the bigger tanks.

https://www.outdoorking-forum.com.au/forum/u...riggs-stratton-pulsa-jet-diaphragms.html

Hope this helps.
-----------------------------
Jack

Thanks CyberJack, i forgot to mention i already replaced the carby diaphagm not too long ago (~2 months ago). I will double check it though to make sure its sitting correctly

Went to mow this arvo and after about 10min of mowing it started to run rough and almost stalling again. Looks like this issue is still haunting me. I pulled the carby off and blasted air through the following holes (see attached photos). Pulled the diaphragm off to inspect and it seems fine, its only 2 months old. Still using fresh fuel and clean air filter. Will put together and run on daylight hours otherwise will annoy neighbours. Any advise will be much appreciated as its getting me down

Hi Mb,


Is that diaphragm one of those Chinese eBay units ?

Cheers,
BB.

I purchased it directly from a local mower repair shop, not exactly sure where their supplier is but i assume they would use reasonable parts

It was still a struggle to start, pull started about 15 times with spraying carby cleaner into the carby inlet to fire it up. Checked gasket between fuel tank and carby is sealed tight. I disconnected the fuel rod (incoming from fuel tank) and air blasted and rinsed it both ways. Hoping to give it a go soon to see if this works.

Hi Mb,

If you pour a small amount of fuel straight down the throat will it initially fire up easily ? If it does then the most likely culprit will be that diaphragm is made of cheap neoprene and is not working as it's meant to.

Many of the mower shops are starting to cheat by buying really cheap eBay parts just like back yard operators are doing now and still charging like they're using "GA spares" componentry. It's a price war between the internet and normal suppliers.

Cheers,
BB.

Thanks BB. I will try sourcing another diaphragm from another supplier just to be sure.

After thoroughly cleaning carby and fuel line, ran the mower for good 25min and no issues with stalling. See how i go next mow.

I noticed i have no more travel on the screw adjustment for the cylinder reel and she is now not cutting well. Have ordered another bedknife as the old one may of been sharpened over the years to a point where it is too short for the reel to contact. Will send the reel and new bedknife to the sharpeners. If i am missing something or havent considered other options, please let me know.

Has anyone had this issue before where the bedknife needs replacing because it has become shorter with the sharpening over the years?

Hi Mb,

If it's become shorter is because someone has been grinding two surfaces and taken too much off the leading edge to try and true it up.

At this point I would simply put a new one on and then have it ground up.

Let your engineer do that part of the job as he may need to shim it or do other things to get it dead straight. Some Sole Plates have been known to develop a slight curve over many years or were not ground perfectly in the first instance.

While doing this get the reel done at the same time as you don't only do one half of the whole job. This way you'll have a good mating pair of scissor blades.

Cheers,
BB.

Thanks BB very much appreciate your advice. Have ordered a new heavy duty Bed Knife blade and will take it along with my reel to get it professionally sharpened.