2 stroke engines - warming up?

[m1spw]

Hi guys

I know that with 2 stroke bike engines you are supposed to let them warm up before you use them. I always leave mine idling for 5-10 minutes before I ride, but I don't really understand why.

Being a total engine novice, why can you run a 4 stroke from cold but not a 2 stroke? And what happens to 2 stroke engines if not left to warm up properly before a run?

Thanks

[andys2]

IMO you'll do it more harm than good by letting it idle for so long before riding it. Leaving it idleing for that period of time will probably just foul the plug. Ride it as soon as you have started it, just don;t thrash it or take it into the 'power band'.
Also use a good quality synthetic 2 stroke oil, this will help keep carbon deposits down if you do a lot of cold starts.

[Trooper2]

You should warm up a 4 stroke as well, best to idle either for just a few minutes then drive/ride them at low RPM until at normal operating temperature. Some new cars BMW comes to mind will actually lower the rev-limiter to around 3000 RPM until at operating temp.

[m1spw]

andys2 said:

IMO you'll do it more harm than good by letting it idle for so long before riding it. Leaving it idleing for that period of time will probably just foul the plug. Ride it as soon as you have started it, just don;t thrash it or take it into the 'power band'. Also use a good quality synthetic 2 stroke oil, this will help keep carbon deposits down if you do a lot of cold starts.

Well I was told to let the engine warm up before riding it properly. It always seems a bit choked when I start it and ride it straight away. About not taking it into the 'power band' or thrashing it, as I'm only 16 its restriced to 30mph so I really have to thrash it to get anywhere unfortunatly.

I'm using very good 2 stroke fully synthetic oil (£10 a bottle! ), so I might be ok.

[Pigeon]

m1spw said:

why can you run a 4 stroke from cold

You obviously haven't ridden a CG125

Generally it's worse to run a four-stroke from cold because the oil is cold and thick and the circulation sluggish. Two-strokes carry the oil in the petrol and have lubrication as long as they are moving.

Leaving any engine to warm up on idle is generally a bad idea as it leads to build-up of gunk, especially with a two-stroke. Generally, if you live in town a bike engine will probably be reasonably warmed up by the time you get out of the 30mph zone, so there's no need to bother warming it up at idle anyway (unless you have a CG125) - your bike has a small engine anyway, so it'll warm up quicker.

[speedy_thrills]

Pigeon said:

m1spw said: why can you run a 4 stroke from cold Leaving any engine to warm up on idle is generally a bad idea as it leads to build-up of gunk, especially with a two-stroke.

Only with an old 2 stroke as far as I’m aware (Those which use traditional petrol and oil mix, i.e. they have an open crankcase), modern 2-strokes and 4-strokes should be idled until well warm. Oil pressure shouldn’t be an issue and modern synthetic oils have a low viscosity even when cold.

That’s a nice bike m1spw, have you ever seen the little 2 stroke 50-80cc bikes they race? I’m surprised you haven’t found the restrictor yet and did some tuning (Mind you they might be electronic these days).

[hugoagogo]

keep warming up your 2 stroke, at least for a minute or two, then go very easy until it's up to temp. the piston can get hot and expand quicker than the bore, leading to a seizure

i like those little DNAs, I'd love an excuse to run one

[Incorrigible]

[quote=speedy_thrillsmodern 2-strokes and 4-strokes should be idled until well warm. [/quote]IMHO engines should be run on a low load not idle from start if at all possible

2 strokes less so as they don't (most) have white metal big end bearings

IIRC there's a really good description of the hows and whys on t'internet somewhere, something to do with the meniscus as the oil gets dragged around the bearing and the shear stability of the oil (again IIRC)

Can anyone confirm or deny this...

[m1spw]

speedy_thrills said:

That’s a nice bike m1spw, have you ever seen the little 2 stroke 50-80cc bikes they race? I’m surprised you haven’t found the restrictor yet and did some tuning (Mind you they might be electronic these days).

I asked, and to have it de restricted it would have to be done by a garage, its very difficult to do it on your own apparently. Not sure how its restricted, it might be electronic (might make more sense as it has a digital speedo) or a washer inside the exhaust. But I don't particularly want to take my exhaust apart to find theres no restrictor in there

>> Edited by m1spw on Monday 7th November 15:07

[MR2Mike]

speedy_thrills said:

] Only with an old 2 stroke as far as I’m aware (Those which use traditional petrol and oil mix, i.e. they have an open crankcase), modern 2-strokes and 4-strokes should be idled until well warm. Oil pressure shouldn’t be an issue and modern synthetic oils have a low viscosity even when cold.

The only difference with more modern two strokes is that the oil is injected into the cranckase by a small pump rather than being pre-mixed in the fuel. Everything else is pretty much identical in operation, i.e. the crankcase still provides primary compression for scavenging. Leaving them to idle for extended periods will still oil the plug up.

[catso]

Two-strokes are more prone to seizure than 4 strokes, I had an Aprilia RS125 for a couple of days as a 'courtesy' bike whilst mine was in for servicing and the guy in the shop was very particular about me warming it up to a certain temp before riding - he said they are renowned for seizing if not, I understand that high performance 2 strokes are worse than simpler 2 strokes due to tighter manufacturing tolerances but this also applies to high performance 4 strokes - F1 cars, for example, need very thorough warming before even starting up.