Warm up first?

[SVGrandad]

Originally Posted by Spokey

Its purpose is to restrict the flow of air thereby enriching the fuel/air mixture while starting the engine.

Choke is required because small droplets of petrol don't evaporate well in a cold engine. By restricting the flow of air into the carburetor, the choke valve raises the level of vacuum inside the throat of the carb, which causes a proportionally greater amount of fuel to be sucked out of the main jet and into the combustion chamber during cold-running operation. Once the engine is warm, opening the choke restores the carburetor to normal operation, supplying fuel and air in the correct ratio for clean, efficient combustion.
Fuel injection bikes alter the amount of fuel / air ratio automatically depending on running conditions.

Oil is deposited in the honing marks of the bore as the piston goes up and down by splash lubrication - these act like tiny ledges to hold the oil which provides a lubricant film between the bore and the piston skirt, and a seal between the ring and the bore. Fuel can wash this oil away so you loose the seal allowing blowby into the sump which deteriorates the oil - and you get less protection of the bore by the oil as a lubricant which can wear away the honing marks and polish the bore - worse case scenario is no honing marks = no ledges for the oil = no seal for the rings = looses compression and burns loads of oil as it comes past the rings.

Also, if the top of the engine is very hot from combustion, but the bottom end is cold because it's not moving and warming up - this can cause condensation - the condensation mixes with the by-products of combustion and creates powerful acids that can damage the internal components. Also for every gallon of fuel you burn, you produce a gallon of water - only when your engine gets hot is this water burnt off ( that's why you get water out of a cold bike exhaust - which is why they tend to rot from the inside out )

I think thats right ...

Spokey

An excellent reply Spokey, but can you elaborate on the lubrication of Chrome plated bores - do these have honing marks to hold oil?

Sorry if I have hijacked the thread

Svgrandad

Now that's a damn good question - honest answer is I don't know. same I suppose with Nikasil bores. I'll have a look into that one.

it's a big problem with diesel engines, the carbon in the oil can, if left and not changed enough, literally grind the bores smooth which polishes the honing marks away - you then get really bad oil burning and loads of smoke out the exhaust because the oil isn't sealing the rings.

Spokey

[SVGrandad]

Originally Posted by Sid Squid

The 'choke' nowadays is rarely that - it's ordinarily an enrichment device, rather than the intake strangler it originally was, and the reason for why we have inherited the word 'choke',
It's needed as when the engine is cold the fuel in the intake charge falls out of suspension and recondenses onto the cold surfaces of the engine meaning that the mixture that reaches the cylinder will be severly weakened. You don't actually need a richer mixture to burn when cold - it's just a mechanism to ensure enough fuel actually makes it to the cylinder to ensure reliable burning when cold.

Mr Squid, why should the fuel droplets recondense on cold engine surfaces? I would have thought that the temperature of metal in a cold engine would be the same as the fuel temperature, so you would not get condensation as such. I have always assumed that a hot engine raises the volatility of the fuel and makes it easier to ignite, but would welcome correction.

SVGrandad

[Sid Squid]

Originally Posted by SVGrandad

Mr Squid, why should the fuel droplets recondense on cold engine surfaces? I would have thought that the temperature of metal in a cold engine would be the same as the fuel temperature, so you would not get condensation as such. I have always assumed that a hot engine raises the volatility of the fuel and makes it easier to ignite, but would welcome correction.

SVGrandad

You're absolutely right of course - when the whole business is hotter things are lit somewhat easier, but essentially the fuel mixture is referred to as an emulsion; a mixture of things that don't really mix that well. At cranking speed particularly the atomisation isn't easy and droplets of fuel are common and require the only slightest provocation to fall out of suspension.

Originally Posted by Spokey

Now that's a damn good question - honest answer is I don't know. same I suppose with Nikasil bores. I'll have a look into that one.

it's a big problem with diesel engines, the carbon in the oil can, if left and not changed enough, literally grind the bores smooth which polishes the honing marks away - you then get really bad oil burning and loads of smoke out the exhaust because the oil isn't sealing the rings.

Spokey

General consensus sugests that chrome plated bores tend to be in two strokes ( not any I've come across though ) and as these have the lubricating oil as part of the fuel mix so we assume that this is enough to lubricate the Parts required - and pistons tend to be turned so the grooves in the skirts will carry a certain amount of oil in them during operation ?
Apparently Nikasil is slightly porous so acts like sintering where the oil would stick in the porous parts ...

Spokey

[ogden]

Originally Posted by Spokey

General consensus sugests that chrome plated bores tend to be in two strokes ( not any I've come across though )

If Nikasil counts as chrome plating for the purpose of the discussion, the RGV has/had it.

I plug and play.

Key in, engine running, ride away.

[ogden]

Originally Posted by BigApe

I plug and play.

Key in, engine running, ride away.

Had any trouble with non-working bikes recently?

Originally Posted by ogden

Had any trouble with non-working bikes recently?

SV. key in, engine start, ride away. (The first time of the day. After this it requires manual pushing along road, jumping, and gabbling and stomping of levers and pedals).

Dullsville. key in, engine start, ride away. (So long as it is above 10 degrees ambient temperature.)

YZF. key in, engine, start, ride away.

[STRAMASHER]

.......as long as it takes to shut the garage door. 5secs. Its all nice and easy 30 limits for me though.