Query Approved.

I'll explain what i know. Fuel consumption of a particular engine, in this context varies with RPM. Higher RPM, more cycles per unit time, more fuel used per unit time.

Now, about the clutch. For example, if you were riding on a level surface in the 3rd gear. You could have the clutch lever fully released, and at 'X' RPM you will have 'Xs' speed. But you could also pull your clutch lever a little and ride. Then, to get 'Xs' speed, you will have to give more throttle, get the engine to run at an RPM greater than X, hence consuming more fuel, and wearing out your clutch.

In a downslope, fully de-clutching, ie pulling the lever fully, and letting the engine idle, will reduce fuel consumption. But it is safer to shift to the appropriate gear, leave the clutch alone, and go down the slope, with a little engine brakeing.

@Ayson has explained suffeciently. But let me add.

Clutch has little to do directly to fuel consumption or FE. The whole story behind FE is a little more complex, however as a thumb rule, it depends on engine RPM in relation to bike speed.

theoretical Example in laymen term:

1. No clutch. You are riding at 60 kmph in plain road. Your engine is reving at 4000 RMP in 5th gear. You have twisted the throttle at about 40%. You are getting 50kmpl.

2. Clutch 1/2 engaged. You are riding at 60 kmph in plain road. Your engine is reving at 8000 RMP in 5th gear. You have twisted the throttle at about 80%. You are getting 25kmpl.

3. Clutch fully engaged. You are riding at 60 kmph in downhill road. Your engine is reving at 1000 RMP(idle) in 5th gear or equivalent to neutral. You have twisted the throttle at about 0%. You are getting 90kmpl.

Oh yes, don't do the math to see its accuracy. it merely an example .

Though I'm interested to know what actually happens when for example

4. No clutch. You are riding at 60 kmph in downhill road. Your engine is reving at 4000 RMP in 5th gear. You have twisted the throttle at about 0%. You are getting ?? kmpl. Anyone?

BTW to relate clutch to FE has more to do with faulty clutch or erratic riding style..

Adding my 2 cents of one line theory - Use less brakes, use less clutch & always try to ride in the top gear without engine knocking; It sounds weird but this is the most optimal way to ride to gain maximum fuel effeciency, gain more clutch life & long life of the engine. So if you ask how to do, then there're some tips I can provide, use throttle control to control your vehicle than brakes, use side mirrors a lot, use a good judegement on other vehicle moves, never miss an overtaking. Looks like going off topic so I'd better stop

clutch should be used only for the following -

- popping wheelies
- revving at traffic light
- generally messing up the running of the bike

Alright for a good clutch life, dont have jerky action ( be a smooth operator )..

Use clutch for shifting only, and disengage gears and bring vehicle to neutral at intersections. you will have long life ( clutch )