Two-Stroke Engine braking

**Mr. Peanut** · 10th March 2006, 18:59

Can extended periods of engine braking damage a two smoke? I don't fancy my
chances, with a seizure, mid corner, up the corromandel ranges!!

Does the lack of fuel mean that the film stays intact, or is the aforemention scenario possible??

I don't want to run my brakes ragged, so I thought I'd ask those in
the know.

**Mental Trousers** · 10th March 2006, 19:19

Brakes slow you down. Engines speed you up. Use them for their intended purpose.

Dunno about the engine braking question, but 2 smokes barely have any engine braking.

**Mr. Peanut** · 10th March 2006, 19:29

That's a bit simplistic, and i'd still rather be keeping my engine close to its powerband.

**Mental Trousers** · 10th March 2006, 19:39

That's as complicated as things need to be. And engine braking has nothing to do with keeping it on song. Just kick it down as many gears as you need to keep it in the right rev range and don't worry about it locking up cos unless something is seriously wrong, it won't. And if something IS seriously wrong then it could seize at any time.

**Mr. Peanut** · 10th March 2006, 19:44

Sweet... and ten characters.

**Ixion** · 10th March 2006, 19:55

Big two strokes have appreciable engine braking, though a 250 is probably not going to be significant. Most two strokes nowdays have an oil pump. This runs faster at higher engine revs. Even on a closed throttle it will provide oil (they are adjustable, so may pay to check adjustment). Often rather than lack of oil it is the reverse - prolonged overrun causes oil buildup in the crankcase and a cloud of smoke and fouled plugs on open the throttle. Used to be an issue (so old wives said) with petroil.

**Motu** · 10th March 2006, 21:47

2 Stroke engine breaking? They all do it...sooner or later....

**pritch** · 10th March 2006, 22:42

Originally Posted by Motu

2 Stroke engine breaking? They all do it...sooner or later....

Often enough so that you should always have two fingers on the clutch lever. That used to be called "stokers twitch".
Not without reason...

**Motu** · 10th March 2006, 22:55

Yeah but.....I've siezed more 4 strokes than 2 strokes.

**Brian d marge** · 11th March 2006, 02:17

Work with me here thinking out loud here

Engine is being driven by the rear wheel, throttle is Just open or full closed, the gas speed will be high as it goes past a venturi, So will produce quite a low pressure at the venturi and after it . So if the engine requires more than the pilot can flow , the low pressure will then look round for the next easist supply be it an airleak , worn carb slide Which will give a weak mixture and a higher cylinder temp. Which could lead to seizure. But if the bike is in reasonable shape and the cooling system is ok I cant think of any reason why not

Dont make the mistake of adding oil it changes the air gasoline ratio ( I always get this arse about face so look it up in a good tuning book) If you have 15 parts of air and 14 of those are Air 1 part is gasoline and you add oil 14 parts of air will still come through BUT the gasoline is now mixed so only 1/2 a part is gasoline and the other now is oil So the mixture will be lean and run Hotter ( less cooling from the gasoline)
See a a reasonable tuning giude or google for confermation anyway
something like that is tea time so I ll buger off before I get all cock eyed,,,

Stephen

**Mooch** · 11th March 2006, 02:52

I think it was only the MVX that had this issue . NSR / KR1 / RGV's Should be all fine

**sugilite:Me** · 11th March 2006, 05:45

It is really only 2 stroke dirt bikes that are used on the tarmac that have this problem, (dirt bikes as a rule are not jetted for long periods of over run) as your NSR has a oil pump, should be pretty much ok. If you are worried, give it an extra large blip on the throttle when you get to the lowest gear your going to use for that corner. If your really worried, put in bigger pilot jets. (to flow more gas on over run)
And yes, engine breaking is entirely valid on a bike such as yours (I ran RG'S and RGV's for a few years)
I always used to just bang her down the gears and throw her in using the engine braking to scrub of that last bit of speed to the apex. (in conjunction with smooth use of the brakes) I found this technique less of a drama on bike geometry than just using the brakes alone.

Don't listen to the 4 stroke tossers who once rode their mates 2 stroke and think they know it all.

**Motu** · 11th March 2006, 08:44

Dirt bikes do go down long downhills - but the speeds will be slower....and the engine hotter.On a road bike with an oil pump I wouldn't worry....although I do! So long as you aren't using lawnmower oil....use something decent.

**Jamezo** · 11th March 2006, 14:45

I've been worrying myself about exactly the same thing. Always made me cautious to bang it down, and caused me to adopt a strategy of using scandalously low revs downhill.

Cause I was working on the assumption that the oil only entered as part of the mixture, but if it's pumped in in proportion to the revs (yes?) then I guess it would be all sweet.

Load off my mind...