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Collection, Preservation and Display of Old Lawn Mowers

Qualcast Suffolk Punch 43s

Lawn mower Qualcast Suffolk Punch 43s

Full choke on throttle full on
Pull to start,starts then have to switch from full choke to half choke back and forth befor it runs okay
Then runs all okay BUT have to keep it on 3 quarter throttle.

If after say 20 minutes I stop it to move to new lawn it will not start again until I leave it for 2 hrs.

I do not know how to set this mower up because do not know the settings for jets and also the thing at the back of carb, it has a little thumb screw with a spring and is connected to the engine with a lever.

The jets are 1 on front of carb set to 1 and a half turns out from full shut, the other one is inside petrol bowl "emulsion tube" I think ,which I do not know if should be full closed, I have set this one to the same as the above.

I think the carb is a "Dellorto carburettor"

Sorry for such a long text

Any help please


Will Sat, 30/04/2022

Carb probs, notorious on these mowers. Certainly first problem sounds like a partially clogged jet.

second prob I’m not sure but bolting s new carb onto these is fairly standard practice.

wristpin Sun, 01/05/2022

Clone carb showing adjustable bowl nut main jet and progression jet gallery welch plug - the silver disc, above and slightly to the left of the block slow running jet screw.

Provided that the Dellorto is kept clean it is a reliable carb. The only reason that folk fit a cheap Chinese clone is that they’ve given up on cleaning the original properly. The emulsion tube is not intended to be adjustable, it should be screwed fully home, however the clone carbs often come with an adjustable main jet incorporated into the bowl nut to give a degree of universal fitting. On the genuine Dellorto make sure that the well inside the bowl nut is clean.

Both genuine and clones have two or three tiny holes (progression jets) which can be seen either side of the throttle butterfly in the carb Venturi . From the exterior they are covered by a welch plug which has to be removed to access the gallery that feeds those jets. Removal usually destroys the plug, so if removing it , you will need to have , or make a replacement. Genuine Dellorto plugs are available; plugs for Chinese clones may be found in a dealer’s mixed assortment box.