2 Stroke Tech

[localboy]

Hey everybody.

What is it about the 2 stroke engine that prevents somebody from getting going wide open down a desert trail the same way they might do on a 4 stroke with no problems?

I have only heard buddies talking about how a 2 stroke engine is not designed to go high rev for an extended amount of time, but a rider should let off the throttle every now and then to let the engine cool, or cycle, or something..... :( They said if I wanted to ride fire roads and cruise at 60 MPH, I should get a 4 stroke. What about cruising at 40 Kmh (steady throttle)?

I will be glad to read whatever articles, etc you can point me to, but I need to be enlightened.

Whats the real story?
Thanks!
Rob

 

[rmc_olderthandirt]

I don't recommend running any engine at WOT for any sustained periods.

Some engines are more tolerant of it simply because they lacked performance to start with and just won't develop a lot of power at high RPM. A high performance engine, two or four stroke, pretty much relies on the operator to know when to throttle back. The downside of having an engine that can provide 100% is that they don't have anything that is keeping you from requesting 101%, and when you do it may not last very long.

If you want to cruise at 60 MPH down the fire roads gear up (change your sprockets) so that you are not holding the engine at WOT to go the speed you want. Personally, I would rather just cruise at 40 MPH.

Rod

 

[_JOE_]

I wouldn't recommend it, but I'm not sure that it will hurt it. I had a 92rm125 when i was about 13 and used to ride 4 miles on the railroad tracks 6th gear pinned. It never let me down. I only changed the oil like 6 or 8 times in the three years I rode it. Ran 2 and a half years on a piston. Rode it for almost a whole summer with a broken clutch plate. The rod that threads into the fork caps had the threads pull out, the forks would drop out an extra 3 inches or so when the front end came off the ground. I had no idea back then what was supposed to be done to maintain a bike. Boggles my mind that it kept running.

 

[2strokerfun]

Honestly, I've never been on a trail or road where I could go full throttle for more than a half minute or so. But if your engine is built correctly, working correctly and jetted correctly, you can run them wide open for as long as you'd ever really want to without destroying them. But don't shut the throttle off suddenly after a full throttle run or you can certainly destroy it. I think a lot of people--myself included--find it a lot easier to vary throttle a bit and just not take any chances on hurting the engine. Especially when I'm seven or eight miles from my truck !!

 

[destructo]

Its like rmc olderthandirt said, you can regear, go taller with the front sprocket a tooth or its really nice when you have a six speed two stroke, absolute heaven for me both my KDX 220 and my KX 125 are six speed, alot faster on top, nice crisp jetting, when you let off the throttle on a hard topend run with a 2 stroke you should really pull the clutch in and gently rev the motor until backed down to the desired speed and gear, because the cylinder gets hot and the fuel keeps your cylinder temps down. Your piston gets alot hotter than your cylinder, the cylinder has water jackets all around it so it won't expand as much or as fast as your piston, and ultimately your piston could seize, that is one of the reasons I run forged pistons they don't expand as much because they are about 10 times as hard as a cast aluminum piston. I also run a little more oil in my premix, I use 32:1 premix which will also alow for a little harder faster riding. The oil in your premix is all the lubrication your piston, rings, cylinder and crank will recieve, the four stroke oil in your gearcase never touches your crank and crank bearings, so I feel it is detromental to your motors health to run a little higher oil premix. I absolutely love the way a properly jetted 2 stroke feels on topend, has an old school hot rod feel to it, hope this helps. :cool:

 

[ericz103]

Forged pistons are tougher pistons as far as taking detonation and what not, although I believe they usually expand more then cast(depending on the alloys). At least I'm pretty sure

 

[motometal]

forged pistons vs cast pistons is just the method of getting the metal into a specific shape prior to finishing, has nothing to do with hardness. If the alloy and treatment were similar hardness would be similar.


To answer the original question:
Overall you would want richer jetting for this type of riding. This includes the pilot circuit, if that is too lean the engine doesn't get oil or fuel when the throttle is closed.

You may want to consider one step cooler spark plug (higher number if it is NGK)

Run fuel with sufficient octane rating

When coming down from high rpm high speed, consider pulling in the clutch and coasting. Back when bikes had the choke on the handlebars another trick was to give it a blip of choke to help cool the engine. Remember, extra fuel (and oil) helps cool the engine.

Add at least one tooth to the front sprocket so the engine isn't revving so high.