Question about 2 stroke fuel economy

[euromodder]

Old 2 strokers are extremely pollutant.
A 4 stroker - say a 250cc - will be a lot better on the environment.

[theycallmeebryan]

Modern marine 2-strokes are direct injected and are much more efficient than carbureted or fuel injected 2-strokes. In a direct injected 2-stroke, fuel is injected right down at the piston as it closes the exhaust port, so very minimal (if any) fuel escapes out the exhaust. Also, in a direct injected 2-stroke, oil is not mixed with the gas, as it is contained and circulated much like a 4-stroke car engine.

Power curves can be tailored for a broader torque range by using (what they call in motocross) a "Power Valve". Its basically a valve that alters the diameter of the exhaust port, which in turn changes the power characteristics of the engine at certain rpm's.

[dcb]

Originally Posted by theycallmeebryan

Modern marine 2-strokes are direct injected and are much more efficient than carbureted or fuel injected 2-strokes...

but in terms of this thread...

Originally Posted by winlie88

I found a dirt bike for $500 - it's a 1980 Suzuki PE 175cc, 2 stroke engine.

[bikepilot]

Two strokes vary wildy depending on the specifics of the design. Some are very crude and don't make huge power or get great mileage (but can still be huge fun), some are very fast, but still use a ton of fuel and others are very nearly on-par with current four strokes.

I have a few two stroke MX race bikes. They are astounding from a performance and reliability standpoint. They make huge power in a light package and seem essentially indestructible and if something does go rebuliding the whole engine takes no more time than a valve adjustment did on my CRF. These are liquid cooled, reed valve and exhaust valve engines with huge carbs and aggressive porting. I've never run one at constant speed on the highway and doubt I ever will. Fairly casual trail riding (which still includes lots of wheelies, powerslides etc) will get about 70 miles from a 3 gallon tank. Street use would be better I think for mpgs.

I also have a kawasaki H1 with expansion chambers. Its a 500cc air cooled piston port two stroke triple. Kawasaki really only had two design goals in mind. First, make the fastest production bike of the era and second be able to sell it for <$1k. They succeeded in both. Its crude, vibrates, uses a bunch of fuel (about 18mpg), smokes and has a narrow power band, but its still huge fun!

Generally air cooled piston port two strokes are pretty inefficient and have narrow power curves. Some manage to do pretty well though, for example Tomos mopeds are pretty efficient and not far off four strokers.

[SoobieOut]

I rode a Yamaha Daytona Special for a few years. It was a high performance version of the RD400, 2 stroke 400cc.

The service manual recommend replacing the pistons every 2500 miles! I could replace them in about an hour, what a pain.

I remember getting about 25 MPG, and it smoked alot, even with oil injection.

I think that barring a huge leap in 2 stroke technology, going with a 4 stroke is the best bet for fuel economy.

Remember when Al Gore was going to outlaw the 2 stroke engine?

[rmay635703]

What happened to the $350 envirofit envirokit?

Can these still be purchased somehow? This would be ideal for my Subaru 360.

Or did they never actually go ahead and sell out to someone?