BMWMCCWA

So what do you do with your airhead when it is running like a bag of poo and you've checked all the normal things, like spark plugs, points gap, points timing and carbs are clean, airfilter is new and compression is smicko. The answer, Esmeralda, is the needles and the needle jets. The air mixture and idle jet setting are all very well for low speed and idling running conditions and the main jet for a 500cc pot should be about a 150 for our low altitude type of work we do but we only really use the main jet exclusively at full open throttle setting, like crossing the Nullabor, etc.

We spend most of our mid throttle life (day to day riding) using the needle jets and they wear, along with their bosom buddies the needles themselves. The petrol is inducted up out of the bowl and through the concentric gap between the needles and the needle jets where it atomises (I love it SO much when I use complicated scientific terms in a discussion). When they wear, they do so unevenly and the fuel does not atomise as well and it does not burn as efficiently.

My Aussie flag bike (R100RT)was running a bit lumpily and not getting the full 360 km out of a 24l tank of petrol, so I suspected that they were the culprit. Constant vacuum carbs are a cinch to open up. The needles are situated within the vacuum tubes and are withdrawn by doing a sort of a combination of a twist and a pull. You want to put the new needle back so that it's at its second lowest of the four positions. You need to compare the length of needle sticking out on the opposing carb, so that they are balanced. The needle jet sits on top of the main jet and is simply held in place by the base of the main jet. I rode my bike right away and felt the difference immediately, much smoother idling. After I got my 16km/litre result on the refuel, I chucked the old needles away.

Brian at Munichs will gladly supply you with new parts for a couple of dollars. If you don't patronise the joint, he'll just spend the morning daydreaming, so go along and stir him up.

John

Thanks John, not even owning an airhead carb bike I found it interesting and educational.

I kept up with the scientific stuff but you got me a bit baffled with the "lumpily". Is that even a word? Or is it in the Oompah Lumpily dictionary?



Wordsmiths [and I know there are a few] please feel free to chip in.

Lumpily is definitely a word....as in Drew's right hand pannier looks lumpily after parking it on gravel scree at speed.

Whether Wightman has used it in its correct context is another matter.

It can mean choppy or uneven.

Wightman has probably chosen not to use choppy running to avoid upsetting our vegan members.

Now I know why you chose to go to Victoria this week Chris. The Three Dams Ride is on in Perth today, Thousands of bike riders chasing each others tails through the hills.

Could have been a case of "Bumpity Bumpity and Squishity Squishity" trying to make your way past them if you had been here.

Apologies to all you wordsmiths in the club

Swampy