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Collection, Preservation and Display of Old Lawn Mowers

Suffolk punch - fuel issue?

I have a Suffolk punch with a delorto carb with the two position choke.

When I got the mower, inside the fuel tank was a little corroded, as was the inside of the float bowl. I have cleaned the tank. I have cleaned the floatbowl with a wire brush on a Dremel. It is spotless. I have fitted a new fuel pipe and filter and cleaned the carb with carb cleaner.

I finally got it running, and got low speed mixture set. Used the mower a few times, but then one day after about 3/4hrs running it cut out and would not restart without choke, even though it was warm.

I stripped the carb, found absolutely no dirt but blew the jet through with carb cleaner. Reassembled, run it without problems. Several uses later, same issue, same solution. This has happened 3 times. Plenty of fuel through the filter.

Is it possible for this type of carb to be stumped by dirt of a scale that cannot be seen?

If so, I am thinking the sealing washer on the the float bowl drain,( which is a bit crumbly) could be the source. If so, where can I get a spare?


any suggestions welcome




gtc Sat, 25/03/2017

Hard to say, but one tip I was given following the de-rusting of a tank is to put a significant U-bend or loop in the (clear tubing) fuel line so that gravity will cause any remaining debris to settle at the bottom of the U or loop.

There's the potential for such debris to continue to come from the tank for quite some time after the cleaning.


wristpin Sat, 25/03/2017

The fact that it runs ok for a while after cleaning suggests that the carb is ok until more contamination is introduced ; presumably from the tank. GTC's tip re the fuel pipe is a favourite of mine.  Coincidentally , this afternoon  I sold a fifty plus year old Suffolk that had been stored for the last 10 to 15 years  and explained to the new owner about the loop in the fuel pipe.

Those drain valve sealing washers may still be available as aftermarket parts and complete drain valve kits certainly are. Try Jon Cruse at the Hailsham Mower Centre.

gtc Sun, 26/03/2017

Another point regarding Dellorto carbs themselves: I have a 12 inch cut "Brand X" 1990 rotary mower powered by an Oleo-Mac chainsaw engine with a Dellorto carb. I was delighted to find that a carb rebuild kit was available locally via a motor scooter supply company.

JohnWillmott Sun, 26/03/2017

I had put an inline fuel filter in - clear plastic from motorspares place. So I Cannot  see how it is debris from the tank.

As an update, cleaned carb yesterday, and still will not run without 1/2 choke. Starts first pull, but will not run without some choke.

will have to have a tinker tomorrow and see how it goes.

wristpin Sun, 26/03/2017

Be aware that if the filter that you bought is for an automotive application and designed for a system with a fuel pump it may have too fine a mesh to give sufficient fuel flow in a gravity fed application. Check for consistent flow into a jar for around 30 seconds.

JohnWillmott Sat, 01/04/2017

With the pipe off the carb it will empty the tank in 5-10mins.

It has also has run for several hours with the filter in place, and the solving the problem on cleaning the carb would suggest it isn't filter related.


Not sure where to go next. Are replacement carbs available?

wristpin Sat, 01/04/2017

Yes there are both genuine and pattern carbs available and I know someone who has recently fitted a pattern one ( almost  quarter the price of genuine) with satisfactory results. A thorough ultra sonic  clean with the Welch plug that covers the slow running and progression fuel gallery removed, should solve the problem but if it doesn't you may regret not having gone the new route.