Track day tribulations

I keep assuring you, my dear readers, that I am not a mechanic. It is about time I write a post that helps illustrate that point.

The last track day I did on the RGV was not the biggest success. The bike was failing to accelerate in the top gears and by the “seat of the pants dyno” was even a little weak in the lower gears. Apart from some cursory inspections and a new set of spark plugs, I hadn’t really done much on the bike since the previous track day, so it was not much of a surprise.  I can’t even say “I should have known better”, because I do know better… As they say: “Proper preparation prevents poor performance”

Anyway, both the bike and I survived the day, so back at home, it was time to work out what went wrong… It didn’t take long – the left carburettor float bowl was leaking fuel. Put simply, the top cylinder was unable to get the fuel it needed when running at full throttle.  The float bowl o-ring had a gap if about 3mm, through which the fuel was able to escape.
Where the carburetors are situated, meant the fuel leak was relatively safe.  The fuel would fall on the crank case, which was hot enough for most of it to evaporate off.

The reason there was a gap in the o-ring was no mystery: I had cut it. Of course, I hadn’t done this without a good reason. At a previous track day I had to take the carburettor apart to clean one of the jets that had become blocked. The o-ring had stretched and no amount of careful prodding, cussing and holding my mouth correctly was going to get the o-ring to fit. One truism of track side maintenance has always been “No matter what spares you have with you, you’ll need something you don’t have.” Faced with the choice of “go home” or “improvise” I chose the latter and cut a small section of the o-ring out.

Why did the o-ring swell? Truthfully, I do not know.  I am guessing it reacted to something, but I could not correlate what the Internet tells me and anything that I remember doing.   I think I may have fitted the o-ring with some rubber grease, but that is designed not to react with it!  Most likely, I got some carby-cleaner on the o-ring and it  reacted to this, although I don’t know for certain.  As I had now discovered, it eventually returned to its normal size, thus leaving me with a gap.

Whilst on the matter of mechanical confessions… That day, when I refitted the carburettor, I broke the thread of the plastic choke nut. These are hollow, allowing the choke cable to pass through them. As a result they are incredibly easy to over-tighten and snap. Without it in place a lot more air would be drawn through the carburettor, causing the engine to run dangerously lean.

Plastic choke nut assembly

There was insufficient thread left on the choke nut to hold against the spring tension, but another RGV owner came up with a clever way of using cable ties to hold the choke nut in place. It was certainly a bodge job, but it easily held up on the day.

So, what did I learn from my mistakes? Lots of things, really!

  1. Do your preparation before the track day, not at it.
  2. If the manual doesn’t suggest using sealant or other consumables, then you probably shouldn’t.
  3. A twenty-four year old bike that you thrash when you ride it needs plenty of TLC/maintenance when you aren’t riding it.
  4. A post track day inspection and service is a good idea.
  5. If you can’t have the right spares with you, at least have plenty of cable-ties!

 

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