Best practise for coasting on a carb'ed bike

[maxp]

Hi guys,

On my fuel injected car, when rolling down a hill, as long as I leave it in gear (and the revs are above 1200), the fuel injectors are closed, meaning the car is effectively doing infinite miles per gallon.

In terms of fuel economy on my carburetor fueled motorbike is it more economical to coast with the clutch depressed or the clutch engaged?

As far as I understand it (but am fully prepared to be wrong!), the pilot air circuit is always open, so a small amount of fuel will always be consumed, but (although the difference may be minor) is it more economical to coast clutch in or out in this scenario?

[esullivan]

I hate word problems. The trains meet in Liverpool in 2.5 hours, travelling 66.7mph. That's my standard answer.

I don't think your car is doing infinite miles per gallon, though.
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Current: '14 VFR800X Test passed 31/10/12.
Previous: '12 NC700S, '11 CBF 125, '04 SH 125.

[MarJay]

Don't do it. If you're tight fisted enough to try to coast on a motorcycle then A) You've got a problem and B) You'll end up damaging it trying to ride it like that.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[_Iain_]

Trying to coast it clutch out is going to give significant engine braking & slow you down to a standstill very very quickly.

Trying to coast it clutch in always made my bikes feel a bit odd & unsettled. It also makes it a lot easier to lock up the back wheel.

Either buy an injected YBR or something like it that'll do 100mpg and bore you to death, or pay the extra 50p a week that riding styles gonna save you. It's a bit of an odd one, with the car i used to coast it all the time but never with the clutch out as it'd loose speed hopelesslly quickly due to engine braking.
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Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[Wobbling Dog]

fuel tap ?

[Kickstart]

Hi

With the engine running, having the clutch pulled will mean less vacuum in the carb and so probably less fuel drawn in along with less engine braking compared to having the clutch released.

With the engine no running having the clutch pulled will mean zero fuel drawn in (but will likely wear the clutch thrust bearing), while having the clutch out will still mean fuel drawn through and likely a very loud backfire when the engine starts again.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[guile]

[Kickstart]

Hi

Engine braking will depend on the gear you are in. Higher gear means less engine braking but there will still be some.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[_Iain_]

[P.]

You won't get engine braking when coasting... you remove the link by coasting, what slows you down is resistance and friction, loss of momentum init.

With the clutch out, you'll stop feeding the engine fuel so it will slow down, on an FI bike that is. That will have engine braking.

[Blau Zedong]

[map]

[pits]

[keggyhander]

Don't coast downhill with the clutch in unless you fancy losing the front end when you have to brake sharply at the bottom of the hill.

[_Iain_]

[Cheeseybeaner]

[Irn-Bru]

Petrol isn't so expensive that it's worth increasing your chances of a crash for. If you coast down a hill you have much less control with no engine braking and if you read the manual of any bike it always tell you to never do it.
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KTM 990 SMT & Suzuki DR-Z 400 SM