Late Merry Tiller Major (new to me)

Just brought a late Major with plastic guard, it starts and operates fine, but it does seem to back fire when I switch it off.

Is this normal or a symptom of something else, I am happy to live with it otherwise

Codes to follow

 Engine
Model 112202
Type 0663-01
Code 84011603

Engine sticker Briggs and Stratton Milwaukee Wisconsin 187cc 4hp at 3600 SaeJ607 (magnetron)

Chassis pop rivet plate
Model No ac3480 Major
Serial 366 001133
Wolsey Webb ltd Edgemond avenvue B24 0Qx

any info please

Backfiring when the engine is switched off is slightly unusual, it is possible that the fuel air ratio is a bit out but it may be best to leave things alone if the machine runs OK. The engine is from January 1984 by the way, and must have been a very early AC3480 Major as the 1983 brochure did not list it, though all other “plastic guard” models were listed, including a new GT which never actually came out. The reason for two filler plugs is because B & S made that engine for hundreds of different applications and found it easier to fit two filler plugs rather than make a different timing case for those who needed the filler at the back or the front. Qualcast did make different timing covers for their engines, and someone had fitted a Qualcast mower engine to a Qualcast B66 rotavator that I bought, it fit OK but with the filler at the back it is difficult to fill, and the drain plug is impossible to get to.

You stand the machine so that the engine is level and fill until no more oil will go in the sump without it overflowing. SAE30 or 10W-40 engine oil was recommended by B & S.

That handle mounting bracket is welded to the chaincase so, though there may be a slight adjustment required during manufacture, the elongation is probably so that the same bracket can be used on the Titan which may have had the bearing in a different place on the chaincase.

The weighted blades are aerator rotors, the other twelve blades are hardened steel and are “hollow tynes” which are designed to take a plug out of the lawn as they go round. I have seen the aerator accessory make £200+ on eBay, I have also seen them make £5.