When I took the original carb off I took one look at the slide, the cables, clips and springs, and the first thought that sprang into mind was a hamfisted fumble with a tiny clip and a jack-in-the-box springing apart of something I'd really struggle to put back together again. So I left it hanging off the end of the throttle/choke cables, ready for re-entry. It mated nicely with the replacement carb and I thought how clever I'd been in hopping over another potential pitfall.
Then, in the name of science, I did some experimental dismantling of the remainder of the old carb, wrecking it some more in the process but discovering the main jet. This brass lug with a precisely drilled nut, or jet, on the end of it is stamped with a number - 130. Further research on the net revealed jets of different sizes, available for the same carb, so it can be used on different machines. I had to get to the main jet in the replacement carb and find out what size it was, without wrecking it. I guessed that I also had better reunite the needles with their respective jets.
Thankfully the vice issue is behind me and now I prefer to work on the carb while it's attached to the bike, so there's no need to figure out ways of holding it steady. It can be a bit awkward - wasn't it Frank Zappa who said, "there's a big difference between kneeling down and bending over." Well, I have to do both. I had to take the battery out to get a spanner in there but this is no biggie, even for me.
The net result is demonstrated nicely in the first photo. The old jet is a 130, the new one a 120. Whatever this numbering stands for, the important fact is that they're different and following my own unenlightened, somewhat plodding logic, the 130 size jet has to go into the new carb, with its own needle, to get me back to where I started some weeks ago.Even more alarming is the difference in needle size (see next photo). You may scoff at me being alarmed by this but if i'm right, and the bike has been running very lean, this oversight could have wrecked the engine. As it is there was smoke issuing from under the tank after my first road test (see TBB 2.0). This may have been overheating due to excessively lean running.
Honestly, I'm so glad I made the effort to check this out, if i'd just reunited the replacement carb with it's original needle, which would have been easy and relatively risk free, I would have wondered what the jet size was until it became an unhealthy waste of my time. Tomorrow I will gas her up, check for leaks, and, all being well, give her a blast up the track. Come on!
