I've noticed that when the engine is pretty cold it will 4 stroke a bit when cold but after it has warmed up there is no signs of 4 stroking at any throttle position. Is this normal? Does this happen because of some thermal expansion of the metal or something?
Is 4 stroking normal when warming up?
- Thread starter arguevera
- Start date
-
- Tags
- 4 stroking cold
What's "4 stroking"? I would imagine a 4-stroke engine is supposed to 4 stroke. What kind of engine are you talking about?
It is a generic HT 80/66cc two stroke. 4 stroking is when a 2 stroke engine doesn't combust its fuel at every "power stroke". This leads it to skip a power stroke every other time (or even more - 6/8 stroking). Usually is caused by too rich of a fuel mixture.
All 4 stroking is not bad. I actually like my two stroke engines to have a bit of 4 stroking as it aids lubrication & helps prevent overheating. I don't want it to occur at the very low end of the power band or at high mid range / to peak rpm. Just briefly & predictably while going up to or dropping back from low cruising speeds... and yes a richer fuel mix is typically the major causal factor.
An expansion chamber can be tuned to assist in inducing or reduction of 4 stroking at specified rpm's as well as jetting/air intake and plug type/heat range selection. Rick C.
An expansion chamber can be tuned to assist in inducing or reduction of 4 stroking at specified rpm's as well as jetting/air intake and plug type/heat range selection. Rick C.
It is better to jet rich than lean, as said above the engine will run cooler. Unless its a problem you should be OK, I have my primary bike set up that way and have been running it that way since 2011.
Yep both you guys are spot on. When racing karts or scrambling back in the '50's and '60's we were jetted oozzy rich at idle which then leaned out at full throttle. Even at that a plug pulled at the end of a race was pretty black not yet fouling but getting pretty close. Point and condenser tech then was also a far cry from today's totally tune able, hot spark CDI's and Iridium plugs available in dozens of heat ranges etc. & rider's learned to keep the revs up to prevent fouling and also cool the motor regardless of what gear we were in on 2 strokes. Power on. Dry sump, full throttle cooling and lubrication (kinda) so to speak & still we all managed to cook an occasional engine. It wasn't exactly a precise science in those days but still fun.
Rick C.
Rick C.