Broken Carburettors - A Terrible Warning

[greenbarn]

Thanks for the heads-up, Pete.  Good info to know.

[Pete]

I've noticed a couple of posts, both in this forum and the UK counterpart, regarding broken Drifter carburettors, specifically one of the pillars for the float pivot pin having broken off. This is a big problem if it happens because there is no way to repair the pillar. It's a bigger problem because the pillars are cast into in the upper carburettor body, and that is a part unique to the Drifter because of the throttle position sensor (TPS) that is only present on the Drifter version of the VN800. These carbs are rarely found on the second-hand market, and although they seem to be available new they are very expensive.

I knew that there were problems with breakage and availability, so when I saw a damaged one going for a reasonable price I took a chance and grabbed it. I had to make a few replacement plastic parts, repair the idle speed adjustment cable and buy a new choke cable, but I ended up with a serviceable spare that I shall keep while I have the bike, and eventually sell on when I'm too old to ride and have to sell the bike.
I was lucky. I nearly fell into the "break the pin support trap" myself. In stripping down the carb for inspection I noticed a particular feature in the float bowl. This could only have the purpose of preventing the float pivot pin from falling out when the float bowl was assembled onto the main body. I only noticed this because of my experience of safety critical systems design where the smart guys design such normally redundant, passive features into systems as backups.

The thing that made me look harder was that there was only one float pin retention feature in the float bowl, not two, as in one for each end. The implication was that the pin could only become loose and move in one direction, which in turn suggested that the float pivot pin was a part of a tapered retention arrangement. Sure enough, when I looked carefully at the support pillars the hole through one was very slightly smaller than the hole through the other and so I knew that the pin had to be extracted in the right direction.
Here is where my stupidity comes in: It was only at this point that I went and had a look at the Kawasaki Drifter workshop manual. This confirmed my observations and, in addition, warns of the necessity to support the pillars when extracting the pin in order to avoid breaking them. I was lucky in that I noticed the design clues before breaking something; it was only my particular engineering specialty that saved me.
I suspect that most of the pillar breakages are caused by people trying to push the pin out the wrong way.

So here is my advice:
# If you are getting carb work done by a third party, explain the issue to them, leave them with a photocopy of the warning in the workshop manual and make it clear that if they break the carb they pay for a replacement.
# Don't remove the float pivot pin unless you have a good reason to do so.
# Be very careful to provide rigid supports for the pillars when extracting the float pivot pin.
# Use lots of little taps with a very small hammer and a good, square faced drift. (If you use an old nail you've only yourself to blame when it all goes wrong).
# When reassembling check everything for cleanliness and corrosion first. Check that the end of the pin wasn't deformed when it was tapped out.
# Tap the pin in lightly – you will need to get it out again one day.
AND, most importantly, when working on anything that is of delicate construction, impossible to repair, hard to replace and very expensive RTFM first!