[maransbantam]

I needed a powerful, not to valuable mower for keeping my allotment orchard tidy. I  bought an old Hayter Harrier 48 off ebay advertised as “spares or repair” bought “as part of a job lot” by the ebay vendor.

The mower has a Briggs and Stratton 4.5 hp MAX side valve engine with a nice simple gravity fed carburettor .
The mower would not start (which I had expected),  so I set about checking the most simple things first.

 I confirmed that I had a good spark. Then I checked in the fuel tank and found that it had quite a lot of water in it. I drained and dried the tank, removed the carbutettor,  drained, cleaned and blew all the jets out.
I put in fresh petrol  -  still it would not  start but did sometimes fire back through the carburettor.

 I thought  I’d better check that the spark was occurring at the right time, sure enough the flywheel key was  intact so I decided the next check should be the valves.

The inlet valve had zero tappet clearance and the exhaust had about 2 thou and its seat was badly pitted. I ground the valves in using my old tin of paste (marked with its price of half a crown) and paid 3 quid for a new suction stick to turn the valves. I filed both valve stems to give a tappet clearance  of 10 thou.

On reassembly it started.

I changed the oil and stripped the carb again because I could not adjust the idle. The idle screw had no effect whatsoever. Today I cut my neighbour’s lawn and it performed well however I still can’t get it to idle properly.

I’ve reached the point now where I’m scratching my head for ideas as to why the idle adjustment does not work and wondered if anyone out there in the cloud has experience of a similar problem or ideas that I might try to solve this final problem.

Thank you for reading.

Update: May 15 2014

Many thanks to the members who responded

I finally fixed this machine today by simply replacing the governor spring on the carb,

I did not realise how important this item is but now i understand it. It provides a negative feedback to prevent the engine over-revving and if it's stretched it will be mpossible to set the carb correctly. | got a replacement off ebay and hey presto,,,,,

[grendel]

perhaps the idle fuel supply in the carb is still blocked with gunk, or the jet needle is damaged.
Grendel

[Ma Lowe]

Hubby has one of these mowers and he says try checking the operation of the air intake regulating vane to make sure that it's operating the butterfly correctly as this controls the revs speed in relation to throttle handle. Have you also checked the air filter is clear?

[Swed]

Which carb?
There are several different with different issues.

Photo would be most helpful.

Leaking air is one of the major problems, and dried membranes the next major issue.

B&S are so simple that it it does not start - it is a silly fault, or a bused coil.
If idling is erratic of refuses to work - is is air leaking or a dried membrane, or both.
However (!) it the petroltank on the 6-8hk sidevalved horizontal Engines is leaking, it will be -very- difficult to get the Engine started since the vaccuum  needed to push up the petrol is compromised...