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Collection, Preservation and Display of Old Lawn Mowers

Qualcast Suffolk Punch

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
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

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

Sorry for such a long text

Any help please




wristpin Wed, 30/03/2022

A couple of images of the carburettor will help determine which of several possible carbs you may have. Meanwhile , for your hot starts try no choke and full throttle.

wristpin Fri, 01/04/2022

That’s a Dellorto carburettor which was also used in one generation of Flymo. This one is from a Flymo so differs slightly from yours but the principle is the same. The small black screw above the model number controls the idle / slow running mixture . In your application it may be hidden behind a blanking plug to dis courage fiddling. The crew above and to the left is the throttle / idle stop which holds the throttle open enough to keep the engine running.


If the carb needs internal cleaning you will have to remove the float chamber ( bowl) . With that removed you will see the slotted head of the emulsion tube in the centre stack. Emulsion tubes can be very difficult to remove and are often damaged by aborted attempts at removal using an incorrect pattern of screw driver. If you get to that stage , seek help before you’ve done irreversible damage and spoiled the chance of extracting it. You’ve been warned !

build Fri, 01/04/2022

Sorry about a lot of pictuers did not know how to post them hence a lot

when i pressed insert andnothing was show I thought it had not gone

Any way thank you for getting back to me

Yes I have those srews as you say BUT what should they be set to?

1.......IE the one on the front

2.......the one inside the float chamber

Also what is the one at the back of the carb  and how to set that

Thank you for youe time




wristpin Fri, 01/04/2022

Should have said, make all adjustments with the air filter element and air box cover in place. 

wristpin Sat, 02/04/2022

The only user adjustments are the throttle stop screw and the idle / slow running screw - both exterior and visible without dismantling. My reference to the emulsion tube was in case you decided that the carb needed a thorough clean. If that is the case I would suggest that you take it to somewhere equipped with an ultra sonic cleaner and, hopefully, the knowledge to safely strip and clean it. 


build Sat, 02/04/2022



Yes I have seen about the emulsion tube , BUT I got it out all okay and

clean all the carb


What I want is the settings for the idle / slow running screw is it full in or half out.


Is the ajustment to the other knob where it has got a spring to it and it looks like it is connected to the engine

Then there is the problem that first posted on here about not being able to start the mower if I switch it off then comeback to it in about 10 mins it will not start, unless I leave it for about 3 hrs or so


Adrian Mon, 04/04/2022

Angus, looking at your photo of the Dellorto carb...


... remind me never to accept the offer of a cuppa from you!


Trebus Tue, 17/05/2022

Carb may well still be the problem but I’d always advise checking valves. Not a huge job to lap and gap them and can make a big difference.