Carburettor rebuild – part 1

My vintage racing carburettors are a pair of 1 & 3/8″ SUs. Nice simple carbs that are easy to rebuild and tune and are a period fitting (note there is no facility for an air cleaner!). The problem is that the set i bought had a few parts missing and were pretty tired. So the rebuild took more time than anticipated. A rebuild kit is pretty cheap as its mostly fibre or cork washers – the only expensive item is the jets and throttle plate assembly (all solid brass) but as they are the parts that wear… they need to be replaced.

Starting with the front carburettor, I found the fuel needle was missing, the bottom of the jet housing had stripped threads, the various internal cork washers had been replaced with hematite liquid gasket the dashpot didn’t fit the carburettor body properly preventing the carburettor actually working at all. In short at some time the carburettors appear to have been abused – but I guess that is balanced by the lower cost… ho hum. Deep breath – lets just get on with fixing all the problems.

The rebuild kit came from Burlen, a company I gained respect for when building the Etype carburettors + I also ordered a pair of fuel control needles as a starting point to get the engine running. Having cleared the workbench to give me some clean room, I managed to get all the components apart and set about soaking the body in de-greaser (for about 6 hours) and bead blasting any steel component that was rusty. The carburettor body itself I dont want to polish in any way – i need it to maintain its old look.

Cutting a long story short – It took all day but as you can see in the photos below one carburettor is now finished… can you guess which one?

The dashpot still has some nasty marks in it where the previous owner clearly had no idea how to polish aluminium, I will need to go over it again with sandpaper to remove them… thanks for that 😦

Antique’ing brass

What you may not be able to see is the above photo is the brass bolt that holds the float chamber lid on… the brass replacement looked far too ‘new’ with its highly polished finish and I want something that looks like it has been there for years… so time to ‘antique’ that brass and give it some patina.

My technique was to first shot blast the bolt to remove the lacquer and polished finish. I then gave it a very light polish with some  fine sandpaper, merely to smooth out the totally flat finish. Next comes the alchemy part. I dipped the brass bolt in vinegar and then held it in the flame of a propane torch for a minute or so, re-dipped it in vinegar and back into the flame… I did this repeatedly until the brass had a sufficiently aged look. Essentially all this does is accelerate the aging process and I am not totally sure I have done it enough as its still a bit brighter than all the other brass on the engine but it is certainly close to the look i was aiming for.

The photo below shows you a comparison between another new bolt and my ‘antiqued’ version. They were both bright and shiny before I started…

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