there have been some international requests asking for some technical tips, especially
concerning fuel consumption, I decided to post the essential contents of my former emails
into Peter Grabo's MOTO-Forum.
Now let me try to explain a solution for consumption problems with moto 6.5's.
Apologizations for my occasional lack of English vocabulary in advance.
In general one-cylinder engines use more fuel compared with multi-cylinder-engines with
the same performance figures. On the whole, this is because one-c-e's oportunity to make
power is via fuel-input, multi-c-e use rotation-speed.
Nevertheless your moto should not use more than apprx. 6-7 litres on 100 km. This also
depends on your driving behaviour as well as on weather conditions. Cold weather with long
sequences on choke rises consumption considerably.
Now, how can you reduce the luxury of fuel-burning?
The easiest way would be to become rich and just forget about fuel prices. You could make
your moto a business vehicle and let the community participate your hard work by saving
your tax. Since you are even saving money by driving a motorcycle instead of a car, you
will even be able to invest more money to create jobs...;-)
In adition you could follow these steps too:
Essentially there are four major issues you can easily handle without special equipment:
1. Use a fuel-saving sparc-plug.
This is a techincal invention using larger and hotter sparcs to achieve an almost complete
burning of fuel. There are some using a dual-sparc technologie, others use less resistance
within the plug and a special construction of the cathode. Mass production types of these
plugs are: "Splitfire SF 416 C" or "NGK D-8 EVX" for apprx. 10 euros
2. Clean the air-filter-foam-rubber.
This makes it easier for air beeing taken in by the carburettor. You should not leave the
3. Check your tyre-pressure.
Incorrect pressure, mainly low pressure, leeds to friction and early use up of tyres.
Friction has to be copmpensated by fuel.
4. Experiment with the adjustment of the carburettor-needle.
Changing the heigth of the needle has a significant influence of cunsumtion.
Each of those issues for itself do not really leed to a noticable reduction of fuel. But
in whole you will certainly notice a fuel reduction effect.
Now let me say some more words to the 4th point, the carburettor-needle. This ist by far
the most effective way to influence consumption. Important is, that fuel is not only
necessary to be burned and to achieve output, it also cooles the piston and valves. So an
extreme lean fuel-air mixture can even "weld" a hole in the piston and so
ruining your engine. The burning of fuel becomes too hot.
The difficulty is to find the right relation between both, fuel and air. A lean mixture
uses less fuel. A fat mixture uses more fuel but is less dangerous to the engine (apart
You can determine a false fuel-air-mixture by looking at your spark-plug. When a moto uses
too much fuel (9-10 liters/100km) the picture of your plug looks like this:
Black soot everywhere. You cannot see the usually white ceramic insulator because of a
sooty coverage. The little "nose" on top is also covered by black. The only
thing that is without soot is the top of the metal-nucleus of the cathode in the middle of
the ceramic insulator.
Having this picture, the mixture is too fat. Less fuel is necessary.
A perfect picture presents like this:
There is only a slight sooty teint at the bottom of the ceramic insulator. The insulator
itself has a light grey-brown coverage. The metal nucleus of the cathode has no soot. The
little "nose" above the metal nucleus is also grey-brown, it may have some black
If yo do not encounter any black soot on the sparc-plug, and you feel that the spark-plug
is somehow "really clean", your mixture is likely to be to lean. Make it more
fat!! You can buy lots of petrol for the price of a burned-through piston...
To be really asured, you can have an CO-measurement of the exhaust fumes. The values of
fuel burning optimal are 1.5 to 2.0 Vol-% CO within 4-stroke engines. This is in very
short the result of a rather complicated chemical oxidation-process from fuel and oxigen.
Are your results less than 0.5 of CO per Vol-%, your mixture is definately too lean.
If you are uncertain in evaluating sparc-plug lookalikes, this might be of some help.
This much for theory. Now we go over to the practical part.
To adjust your carburettor-needle you don't need much. Unmount the tank. Use 8mm ratchet.
If you like you can unmount the seatbench too, but it should not be necessary.
Now you can see the top of the carburettor. You see the black cap, fastened with two
Phillips screws. In case of dirt, clean up! OK, loosen those screws, you lift the cap.
Underneeth you will find a spring coming towards you. Carefully remove the spring and lay
it on a piece of old cloth. Don't put it on the seatbench. It almost certainly will drop
down and makes you mad finding it again.
Then you look onto a black rubber membrane. It's lower end is fastened to a plastic or
metalic cylinder. Have clean fingers! Carefully lift the membrane and pull it up together
with the cylinder. Within the cylinder you see the carburettor-needle.
Turn the cylinder upsidedown and the needle will drop into your hands or cloth. Don't let
it drop somewhere else. Now inspect the needle.
It's function is as follows: The underpressure generated by the engine will result in an
upward movement of the cylinder, lead by the rubber membrane. The needle resides in the
main jet and locks it, like a finger in a bottle. As the vacuum rises the needle will move
higher and so it opens the diameter of the main streaming jet. More and more fuel is been
taken into the cumbustion chamber.
Now, the ruel goes like this: The higher the needle is lifted, the more fuel is burned.
For adjustments the needle offers five notches on its top. My needle also has a little
plastic-ring, wich is pressed onto it. A little metal clip on top is used to change the
position of the needle. Setting the clip into the higest ring (the one on top) of the
needle, makes the needle come more down. It will cause less fuel consumption. Don't forget
to adjust the tiny
plastic-ring by pressing it back against the clip.
I recommend to set the clip in the middle first, afterwards rising it up step by step.
Always have an eye on the colour of your spark-plug.
My clip is on the last position (needle down). Some drivers encounter different engine
characteristics. This is to be tesed individually. I feel no significant difference after
my adjustments. I can say that my moto uses something in between 5 - 6 liters/ 100 km.
Before, I had about 10 liters in Winter with much choke. In spring I was using about 8-9
Evaluating the colour of my spark-plug, my mixture was far too fat. After all it also
depends on your driving style. Well.
I Hope I could help you with my information. Perhaps you tell me more about you and if you
succeed in fuel-saving? So have fun with your moto.