A few weeks ago I decided to use my field trimmer to cut down the grass and weeds in the orchard. The 150cc 4-stroke petrol engine was running rough and not up to the task. After some research at the University of YouTube I established the problem was linked to the by-pass jet on the carburettor of the machine. Use "petrol mower engine surging" as a search term in Bing or Google. The machine is a bolt for bolt clone of a genuine Hyundai HFT56 field trimmer.
After establishing the identity of the Chinese engine, I placed an order for a replacement carburettor, as I've never had much success in servicing carburettors in the past. When I raised the order, it was marked in stock, but the day after the vendor emailed me to say they were out of stock and it would take a few weeks for supplies to arrive in the country.
I waited 6 weeks for the new device to arrive without success, before cancelling the order. The day after, I found a vendor who had genuine Hyundai parts in stock. A replacement carburettor arrived within a couple of days. When I tried to replace it I discovered the fuel pipes on the field trimmer engine were rotten, so I had to order new fuel pipe and also appropriate fuel pipe clips. Once they'd arrived I set to work. I took plenty of photographs to ensure I knew how everything fitted together, but within a couple of hours I had the field trimmer working again.
I decided to service the old carburettor, and retain it as a spare. When I disassembled the old carburettor I found it was clean inside, but that the by-pass jet was indeed clogged up. I tried using carburettor cleaning fluid, but that would not shift the blockage. I tried a carburettor needle tool, but the orifice was blocked solid. Eventually I had to dig out my ultrasonic bath. Placing the clogged jet in a small ziplock plastic bag, half filled with carburettor cleaner and isopropyl-alcohol, floating in a half filled ultrasonic water bath, I was able to soften the jet blockage with two 30 minute sessions in the ultrasonic cleaner bath. I then used my finest cleaning needle to restore the jet opening. This needle measured at 0.4 mm diameter. It was a tiny hole, easily clogged by gelled E10 petrol which ages in a few weeks.
