So the first thing I noticed today is that in Carburettors part 1 the carb I tore-down was way too clean (although not perfect). This was because I had actually given it a bit of a scrub when I took it off the bike during tear-down. In this post I will include some pictures of the second carb which actually show the true starting point.
When the carbs were apart as per the last post I started cleaning everything up. First, all the existing o-rings were removed. Most came off easily with a pair of needle nose pliers, except for the choke (enricher) o-ring which was very fine and hardened. I used a sharp tool to remove that one.
For the small parts I used the William Plam suggestion- I put all the parts in a small plastic pot and covered them with wheel cleaner. Wheel cleaner is a dilute hydrochloric acid solution and technically probably not the best for brass parts however it seems to work well and if it’s good enough for William it’s good enough for me. I left the parts in the bath for about half an hour and then removed them, rinsed them with isopropyl alcohol and blew out all the jets with compressed air.
It’s maybe worth noting here that I don’t have a compressor (another big ticket item on the list along with lathe, mill, sandblasting cabinet hahahahhah) so I just used compressed air in a can to blow out the jets.
As for the large parts- they were scrubbed in my version of a solvent tank (plastic tub) with degreaser using a scotch-brite pad and a tooth brush. When everything was clean all the channels were blown through with isopropyl alcohol spray and compressed air. Everything seemed to be flowing nicely. I then polished the aluminium with Autosol aluminium polish and used a Dremel polishing attachment for some of the areas. Another tool which can’t be underestimated is the humble q-tip dipped in alcohol. Surprisingly abrasive and good for getting into corners.
Prior to rebuilding I laid out all the gaskets and o-rings and got organised. The rebuild kit which I got from Munich Motorcycles has a little o-ring size guide in it which was quite useful as was the Boxer2Valve video.
I started by re-assembling the butterfly apparatus. There is a small dimple on one side of the plate (this is tiny and if you can’t find it during disassembly you should mark one side of the plate). The dimple goes up and faces out which orients the plate in the correct manner. I replaced the o-ring on the spindle and put it into the throat of the carb. Then the butterfly plate was slid into place and the screw introduced but not tightened. The goal here is to align the plate perfectly so there is no light showing at the top and bottom when held up to a window. it takes a little jiggling and you can help yourself by holding the plate in place with a finger from the other side. when it was right I tightened one of the screws down and removed the other and applied some medium strength threadlocker to it. Then I tightened that one down but not fully and repeated the process with the other screw. Before final torquing I held it up to the light and checked the alignment.
After the butterfly assembly I replaced the throttle return plates and screw. The screw should be set so it stops the throttle fractionally before the butterfly contacts the carburettor throat.
Then I moved onto the choke (enricher). I replaced the o-ring on the shaft and put the valve back together in exactly the orientation it had been (photographs help here). Then I applied a light smear of non hardening gasket sealant to both sides of the new gasket (I used Hylomar). This is to try and prevent the gasket suck-in problem. I only put the sealant around the U-shaped portion of the gasket.
Next I replaced all the jets in their respective positions with new o-rings. The o-rings were quite hard to get onto the mixture jet and idle jet and the biggest o-ring goes onto the main-jet holder barrel. The mixture adjust screw was tightened all the way and then backed off 3 half turns. Then I replaced the float. I used the same technique as the Boxer2Valve video to determine float level but found it to be pretty much spot on without bending the tabs. Before replacing the float I hung a new needle valve off it and then tapped the old pin back in from the knurled side.
Finally I replaced the float bowl gasket and the float bowl and then the slider mechanism. I had new diaphragms but the old ones looked brand new so it seemed a shame to discard them. I kept them but I might live to regret it! Here are some before and after photos.
