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I am just about done with my motorized bike project and can't find some answers I'd like to have.
I know a 2-stroke is dirtier that a 4 stroke at comparabe power levels, no matter how well tuned the 2 stroke may be.
I have gotten and read many comments about how a 2 stroke on a bicycle is an environmental nightmare and I should walk instead. Well, when walking is reasonable I do. Groceries get mighty heavy after a 7 block walk, which is where the least expensive store is. And a visit to a friend 5 miles away requires a pretty good effort when I'm taking lunch. In those cases, I drive. My van gets a solid 31mpg, so its not bad at all, but.... this bike will easily get 140mpg, and with some tuning, 180 might be reasonable.
When we see the plight of pollution in other countries that have tuk-tuks and rickshaws and 2 stroke motorcycles all over the place, they are always belching toxic fumes. If you watch those people drive, it's pretty obvious that the machines are in very poor tune, over oiled and too rich. It is also pretty obvious that the environmental impact they have is not a consideration. It just isn't on their radar. The machine is a tool to do a job. Their radar is filled with economic objectives, not environmental.
My bike would not be driven if it spewed like that!
First, it is a bump start, which means that it will never have to accelerate me from a dead stop. The minimum speed to start it is 6 or so mph. Anything less and it doesn't have enough rpm to produce any useful power for me.
Second, it will be driven with a mind for mpg. Remember, I drive a minivan and get 31mpg from it all the time!
Third, it'll be tuned to the best of my and 3 other 2-stroke whizzes around here can get it.
Forth, I'll be using Amsoil 2 stroke oil at 100:1 mix

So, given that background and criteria, I find it very very hard to accept that my bike will be worse environmentally than my minivan for the same trips. The van gets 31, the bike a minimum of 140 - almost 5 times better. The way I see it, even if the bike is 5 times dirtier, its a wash emissions-wise, and I have consumed 5 times less petrol on the bike.

I'm not married to the idea that my motorized bike isn't worse that driving the van, I just don't see how it's true. I researched on the net but couldn't find anything helpful. It's almost like everyone else thinks the only way a 2 stroke gas engine can run is bellowing blue fog!

Help me understand this ok?

Thanks
Keith

PS, I live in one of the greatest snowmobiling areas you'll find in the US, and I won't get on one for the fact that I refuse to smell like a gallon of pre-mix! I will be working very hard on being sure the bike doesn't do that to me!

When I read the title of the article I thought it was going to be about old classic Saabs. The original Saabs were two stroke engine power. Attached to the underside of the gas cap was a label to remind the owner to add some oil with the gasoline. Amazingly enough, Saab won rally races with those two strokers.

Don't know what to tell you on the two stroke bike

Hi Keith, I am not an expert but here are a few things I know.

-A 2-stroke will usually emit huge amounts of unburned hydrocarbons compared to a 4-stroke, because some unburned fuel and oil makes it out the exhaust.

-Your van has a catalytic converter, your bike likely does not. Cats are usually 90%+ effective at getting rid of NOx, CO, and hydrocarbons. So even if your van burns 5x more fuel, it will likely have lower NOx, CO, and HC emissions.

-Where your bike will be better is in CO2 emissions. CO2 is proportional to the amount of fuel burnt, so the bike will emit about 1/5 the amount of CO2 your van does.

I might be able to help, I have a small amount of experience in small engine emissions tests as well as chassis emissions work. I need more info:

1. What is the displacement of the 2 stroke engine you are using?

2. What type of engine is it? Is it some manufactured scooter or a home brew kit.

3. When was the engine manufactured?

That should be enough info to give you the emissions standards, if any, of the engine you are using. The emissions standards will be in grams per kilowatt-hour if it is a small non-road utility engine. The emissions limits can then be used to develop a grams per mile based on your average speed and what you estimate the power output to be. One note, most newer 2 strokes emit less HC and NOx at wide open throttle than at idle or part throttle.

I heard a statistic a few years ago that your average 4 stroke lawnmower is 6 times worse pollution wise than a car. Can't imagine what a 2 stroke compares to, which is why all of the boat motors are switching to 4 stroke. Having said that, Bombardier (the new owners of Johnson and Evenrude) claims to have made a 2 stroke motor cleaner than the Honda 4 Stroke which is the EPA standard. Having said THAT an old moped isn't a cutting edge outboard motor. Honda historically made very few 2-strokes and there are some really cool 4 stroke small displacement bikes around. I have a 1964 Honda CT200 enduro type thing. Its got a 90cc four stroke that'll go about 150 miles on a gallon of gas and has a top speed of 60 mph. The later models were even better with a sohc engine. There are a lot of different things they put out throughout the years from 25 to 90cc.

If you are really concerned with the polution levels coming off bike, you could try to direct a portion of the exhuast back into the intake... maybe 10-25%. Don't think it would hurt power too much, and I'm sure it would reduce the harmful output.