Revving a cold engine

[Viney]

So then, apprently its bad to rev an engine when its cold as the oild system isnt at its best etc etc. So then i ask you, why do 'chokes' rev the engine if its going to accentuate wear? Also, why do we need a choke?

Just somethings that always puzzle me.

Puzzled of Bromley

[rictus01]

Operating temp !

Engines run better within a certain temp range, before they have reached it they are liable to stall on standard running settings, chokes increase the fuel flow (which inturn speeds the engine a little) to prevent this.

Cheers Mark.

What Rictus said, but also, what do you call "revving" a cold engine? I'll start mine up & "twitch" the right grip to make it jump to around 4k. That's mainly due to the exhaust.

I wouldn't go above around 4k RPM though personally. For that I'll wait until the engine is warmed nicely. Revving a little also probably helps kick the oil around a little too, but that's just a guess.

I think the choke is fine because it is a constant engine rev; theres lots of stress on cold parts that are accelarating, decelarating, accelarating when you are blipping the throttle

I think for the SV, suzuki recoomend a choke idle of ~2500 rpm for 30 secs, then turn it down

Matt

[DarrenSV650S]

Here's another question.........why don't cars have an electronic choke to warm them up?

[rictus01]

Originally Posted by DarrenSV650S

Here's another question.........why don't cars have an electronic choke to warm them up?

Either
a. because most have fuel injection
b. because they have manual chokes (OK older ones)
C. they do have auto chokes of one kind or another (sevearl different types, ford used to use a wax type one, when the engine got hot enough the ax would melt and release the choke).

Cheers Mark.

[Sid Squid]

The choke function is to allow enough fuel to reach the cylinder as a gas which will burn. When the engine is cold the fuel drops out of suspension in the intake gas and condenses as droplets of fuel on the cold surfaces of the engine before reaching the cylinder, the engine doesn't require a richer mixture when it's cold, we're just adding more fuel to the mix so that something like the normal amount will actually make it to the cylinder.
The choke should be used to a degree that allows the engine to start easily, should be set that the engine will run at it's lowest reliable and smooth speed, and only used as long as is absolutey necessary. Using my Kwak as an example, my being used to it I know that it never needs more than approx half the choke to start then is backed off almost all the way, I drive off and then turn the choke off completely about half way to the end of my road, (about 100yds), if it's very cold out and the engine won't tickover reliably I'll use a dab of throttle to keep it alive rather than use the choke.
The correct use of the choke won't make the engine rev unduly, overuse of the choke/running the engine too quickly when cold can accelerate wear as the excess fuel can cause a condition called borewash, where a grossly rich mixture washes the oil from the cylinder.

Originally Posted by Sid Squid

the fuel drops out of suspension .

Mr.Squid..Ah ha....now we be know why Ducati Moto GP bike be so fast on only 21 litros of fuel! They hiding more in suspension!

if only ducati (and all manufacturers for that matter) transferred the large tank aspect of motogp to the road bikes rather than the bloody paintschemes! gsxr with 21 litre tank? yes please!

[DarrenSV650S]

Originally Posted by rictus01

Either
a. because most have fuel injection
b. because they have manual chokes (OK older ones)
C. they do have auto chokes of one kind or another (sevearl different types, ford used to use a wax type one, when the engine got hot enough the ax would melt and release the choke).

Cheers Mark.

But you never hear cars revving more than tick-over when they start up?