Wood Tractor 3: new carburettor

Last month I had a problem with the tractor not starting and I ended up replacing the carburettor and the fuel lines. I also improved the ground clearance with a “pulley cut”, and this post also shows some modifications I made to the car trailer I use to bring firewood home from Century Wood.

I’ve also made this video about the fix, if you’d prefer to watch that instead.

The problem with the tractor started with it losing power and almost stalling. For the last minute or so while the engine was running I could only keep it going by closing the choke, and then eventually it wouldn’t run or start at all. There was plenty of petrol in the tank and the fuel line was ok so the next thing to look at was the carburettor. 

I took the tractor home and took the carb off to have a closer look. The carb itself is the complicated bit in the middle with fuel and air pipes coming out of it.

Here is the carb on the left with the aluminium fuel bowl removed and on the right. This fills up with petrol. The black dot in the middle was the problem. It’s the end of a plunger worked by an electronic solenoid underneath the bowl, but it was covered in black gunk and jammed. 

I could probably have just cleaned it and put it back together, but instead I bought a new carb kit which included a new fuel line, fuel filter, clamps, rubber gaskets, and both air filters for £20. Some of the carb components wear out and I almost got a new one last winter as part of my original overhaul of the tractor. I reused the ducts for the air and petrol-air mixture but gave them a wash with soap and water. 

So this is the new carburettor installed. The shiny brass tube is the solenoid, which is the bit that had jammed on the old one. To the right the new fuel line and filter. The old rubber fuel line had started to perish.

I got a laser tachometer online for £11 and used it measure the engine speed as I adjusted the tuning. At full throttle it runs at over 3000 RPM. 1600 RPM with the throttle as low as it will go. If I tuned it to run any slower then it stalled. In this picture you can see the small machine screw used to adjust that.

With this kind of tractor you want minimum throttle to be as low as possible. Since you can’t change gear while you’re moving you have to set the gear while stationary with the combined brake and clutch engaged and then set off. So if you start in 5th gear and the throttle is too fierce, you do a wheelie or even flip the tractor over. Once you get going, then you can whack the throttle up. 

On the right here you can see the bottom end of the drive shaft. It has two pulley wheels: one at the top for the drive belt which takes power to the gear box and back axle, and a bigger one at the bottom which powered the original mowing deck which I no longer have. The problem is that the bottom wheel reduces the ground clearance and exposes the drive shaft of the engine to impacts from below.

So I decided to cut it down while I had the tractor at home. A brand new one is not that expensive if I decide to reverse the cut. I did originally think about using that big pulley wheel to power machinery. I took the pulley wheels unit off and cut it down to size with a mains powered angle grinder. You can see it back in place on the left. On the right you can see the way I had to butcher the bigger wheel to get the angle grinder into the gap between the wheels and cut the shaft short. In the foreground is the original long bolt that held the pulley wheels on to the drive shaft. And then shorter 7/16 inch UNF bolts which I had to order online. You can’t readily get imperial size bolts in the UK as we’ve gone over to metric. I notice this with spanners too with the tractor: I use adjustable spanners a lot more since I only have metric ones otherwise.

This photo shows the end of the pulley wheel unit with one of those bolts, the original sprung washer and a new penny washer to close the tube end off. On the right you can see the end of the steel skid plate which I added to protect the drive belt. I might make a longer skid plate now to cover the pulley wheel too. 

With the tractor back in business, I could use it to help with the forestry work. This plantation poplar tree is on the North Ride and has grown really awkwardly due to the disease which attacks their forks. I’m gradually removing the poplars to favour native trees, starting with bad specimens like this. Then the same tree on the ground, and then with some of the rounds in the trailer to be pulled to the Barn by the tractor and stacked there to dry. I probably won’t use them for firewood as they are difficult to split and difficult to keep dry. They are great for big bonfires though once dry, and good as chopping blocks for smaller firewood. There’s even one being used to help a cat reach a window sill!

These are pictures of the car trailer I use to take the tractor to the wood and to bring firewood home. I added a jockey wheel to the towbar when I bought it last year. This means you can stand the trailer horizontally while you load it up. The centre of gravity is over the big road wheels as you would hope. However if the trailer tips backwards at all, the load can start to slip and then the trailer tips backwards completely.  In particular this means you can’t move it around once loaded up, which means keeping it hitched to the car to be safe.

I’ve solved this problem by getting two more jockey wheels and clamps. They’re on sale in various places this time of year as the camping season is finishing. I put clamps on each back corner so you can add a jockey wheel. The only issue is that you can’t turn the handle once they’re attached, but it’s easy to loosen the clamp to allow the whole jockey wheel unit to be moved up or down, or even taken off. I used this setup already, filling the trailer with firewood and then pulling it to the back of the car to take home. I covered the firewood with a tarpaulin to keep the predicted rain off, and a new cargo net which worked very well.

Hopefully I’m all set now for another winter of firewood harvesting.

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