Friday 18 November 2022

Carburettors Rebuild

When I first started to clean the carbs back in December 2012 they were totally junked up and looked in a right state.

Once I did get them all cleaned up they've sat in a box waiting for the right time. And that time was now!

Before I could start putting it all back together I needed some new parts. The jets and the jet bearings were pitted and worn. The throttle return springs were rusting away. So I placed another order.

Once that order arrived I wanted to test fit the carbs to make sure I knew what I was doing, but also get more familiar with them as I knew tuning the carbs it very important to achieving a smooth running engine.

I had already attached the exhaust manifold covered in this post: Exhaust System Fitting

First to be fitted in the inlet manifold that slots on to the studs.

Then you can add the washers and tighten the nuts.

Then you need to fit the spacers which have gaskets either side of them.

I then want to check over the float valves having previously cleaned out the bowls I knew they needed attention.

I didn't know if the floats themselves were sound. 

So I removed them by pulling the pin. I then weighed them down in a mug of water to see if they were cracked at all. 

Thankfully they did seem ok and that meant I could check the valves as I didn't try cleaning them before. I unscrewed the valve to see if the valve or the pins moved at all.  

They didn't so I removed the valve and gave it a really good clean and a degrease. After cleaning I tried again the valve started to work perfectly. I took the decision not to replace the valve for the time being, but I can see some wear on the left of the valve below. But as the pin on the right freely moved in and out I decide to keep it and carry on. 

Update: After driving for a few miles I started to get fuel leaks from the float chamber gasket. This was caused by the worn valve below. I replaced both valves with new and it stopped the leak. Lesson learnt!

I know it is important to check the gap between the float and the valve. I found this online which explains what that gap should be.

Mine did need to be adjusted slightly. But it look ok to me.

Depending on how she runs I'll invest in new valves at some point in the near future.

I could though now bolt the float chambers to the main carb body and attached them to the inlet manifold.

As you can see I have not played around with the linkages. I'm too worries that I'll mess something up and I just want to get the engine started.

I might find that the linkages have worn which will let air get drawn through the worn spindle but again I'm hoping it will be ok. 

When I first saw my carbs I wasn't sure why it didn't have a proper heat shield. I did end up buying one and trying to fit it. It was then that I realised why mine didn't have one. The exhaust manifold is not a standard one and the pipes come out much closer to the carbs. This prevents the normal heat shield from being use, hence why I had this bracket fitted.

Which attached to the inlet manifold studs.

Before you tighten the main four bolts to secure the carbs you must attach both throttle and choke linkages. Make sure you get the arms in the linkage slots on both as well. 

It is important to balance the carbs. Part of that is done by unscrewing the linkage bolts as seen above and below. But this should be done once the throttle and choke cables are correctly attached.

You can then tighten up the four main bolts.

Then attached the three springs, suction chambers and pipes, ensuring all the clips are nice and tight to ensure no fuel leaks.

That includes connecting it to the main fuel pipe from the pump.

Next up was fitting the throttle cable. My old one was destined for the bin!

I used it though to make sure the new one I bought was the correct length. Some people report issues with the cables wearing out and many people recommend using push bike brake cables. Which is what I did. 

You need to check the ends of the cable to make sure you cut the right end. For me this below looked like it would fit best in the pedal arm.

Cut the other end removed the cable entirely and then cut the outer sleeve to match the old one.

Replace the protective cap.

And fitted the cable into place. It did fit very well.

I could then replace the outer sleeve and then connect the cable to the throttle linkage on the carbs.

Job done!

Before I could try starting I had to set up the carbs with all the adjustments which I will cover in this post:

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