Fuel on: tickover normal, fuel off: tickover fast!

fishsponge · Post by **fishsponge** » Wed Feb 11, 2009 12:15 pm

Here's a question...

I came back from a journey a week or so ago and stopped outside my garage. Upon stopping the engine, i also turned off the fuel tap.

I then went to open up the garage etc... and started the bike back up with the fuel tap off (this was an accident).

By the time i had ridden the few metres into the garage (up a slight slope and over a bit of 2x4") and put the bike back on it's centre stand, i noticed that it was ticking over rather fast.

I experimented with the throttle to see if the cable was stuck etc... and tried various other things too.

However, it turns out that the tickover speed was eventually reduced by my opening up the fuel tap!

NOTE: When turned off, my fuel tap does not leak at all, and I have brand new corks.

What on earth was going on here???

paul knapp · Post by **paul knapp** » Wed Feb 11, 2009 12:32 pm

G,day Richard, the fuel level drops in the float bowl when the tap is turned off with the engine running. This lower level causes the mixture to lean off, and since a lean mixture burns quicker and hotter, this increases the combustion cylinder pressure which in turn pushes the piston a little bit more increasing the engine revs.

Paul

fishsponge · Post by **fishsponge** » Wed Feb 11, 2009 2:34 pm

which in turn sucks more fuel in from the float bowl, thereby emptying it faster, right?

i guess it would eventually stop too, of course!

Interesting effect, anyway!

rex.webb · Post by **rex.webb** » Wed Feb 11, 2009 6:19 pm

This is a fault that shows itself when you have the fuel level to high in thge float chamber.
You must be using more fuel than you need to.
Make sure u alter the level as this extra fuel washes oil from the cylinder bore.!Thus causing greater wear to occure.
Ride with Care and Live Long.

alanjennings · Post by **alanjennings** » Wed Feb 11, 2009 6:43 pm

Paul, I'm glad to hear you are O.K!! I see Lenard Cohen touring in Aus. has donated 90,000 grand from his "pension fund" for the fire survivours.

paul knapp · Post by **paul knapp** » Thu Feb 12, 2009 2:06 am

Thanks for your kind thoughts Alan, I am about 450miles east of the area. Relief fund is now at AUD$44.5 million. Over 1,600 square miles gone. 1,200 houses. 21 fires still out of control.

Paul

fishsponge · Post by **fishsponge** » Thu Feb 12, 2009 4:17 pm

rex: when the fuel tap is open, the bike ticks over perfectly.

when the fuel tap is closed, the tickover speed slowly increases.

Are you sure this means my fuel level is too high in the float chamber?

The reason i say "are you sure", is that i basically don't understand!

Regarding using more fuel than I need to during normal riding (with the fuel tap *on*), i do use more fuel than i need to - i get around 65 miles per gallon (it's a 1966 350cc), but i put this down to the knackered piston rings which i still need to replace...

itma · Post by **itma** » Thu Feb 12, 2009 5:24 pm

He's been drinking the diesel again fishy; you cannot alter the fuel level in a monobloc or concentric cab, its fixed.
What you describe is a common phenomon, as the fuel is used up it creates a weak mixture so for those last few secs it speeds up.
Nothing at all to worry about, leave it be.

bjork · Post by **bjork** » Thu Feb 12, 2009 8:27 pm

Hi Fishy, as already said, it's nowt to worry about they all do that sir!

I can disagree with Ken on one point though, ie. float height adjustment IS possible on Concentrics at least.
I used to think it wasn't possible till I fitted a pair of new 'Ready to go' carbs to my G15CS.
It took me a while to twig why the tickler seemed to take ages to flood one carb and the other wouldn't tickle at all!
If you look in the float bowl, the seat for the needle is a brass insert that is a push fit, it can be gently drifted in and out-thus adjusting the fuel level.
Don't ask me what the correct level is, I did it by trial and error in the end. On my bike the seats needed driving in deeper-about 40/60 thou (1/1.5mm) and +/- a gnat's fart as well. (E-marked gnat of course)

paul knapp · Post by **paul knapp** » Fri Feb 13, 2009 12:00 am

Hey Fishy, don't go worrying about that carburettor, It's running just fine.
How about doing another video from that helmet camera you have, we are all still amazed how the traffic simply gave way to you at that round about and else where on those narrow roads, as seen on your ride to the aviation museum.
Down here, we riders are considered as a moving target by the car drivers and 4x4 wannabe's, who's main objective is to push in front, whenever there is a motorcycle in their view.

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