Whats the difference between a 2 stroke and a 4 stroke, is it really worthy select a boat based on this?

2 strokes have half the moving parts as 4 stokes. 2 stokes weigh half as much as 4 stokes witch drastically effect the way a boat performs. 2 stokes cost much less then 4 stokes. If your going to be in salt water go 2 stoke trust me on that. Good Luck.

Both have advantages and disadvantages, the biggest being that some bodies of water are classified as 'Four-stroke only" but not many. 2 strokes: Lighter, cheaper, faster acceleration, simple & easy to repair but more pollution (including noise), must mix oil with fuel, a little rougher to run (idle) and can be harder to start 4 strokes: Less pollution, smoother running, accepted in any body of water, good fuel economy but heavier, expensive to buy and repair (more parts and harder to find) and not as powerful as a 2-stroke at same rated HP. Four-strokes are improving and I think will be the norm in the future but for the time being, I would go with the 2-stroke, imho EDIT While I agree with Brian, and I DID recommend to go with a 2-stroke, the descriptions between the two are accurate in general terms, and may even be more pertinent as he mentioned that he was looking at used.

4-stroke engines are better because they're more reliable and they pollute a lot less (you may not be thinking environmentally, but believe me you'll get tired of smelling outboard motor exhaust very quickly). Here's the best illustration of the difference: Cars and most lawnmowers have 4-stroke engines, and chainsaws, edgers, and weed trimmers have 2-stroke engines. A 4-stroke engine takes gas and oil separately, but a 2-stroke engine requires gas/oil mix. That's another advantage of a 4-stroke engine -- you don't have to mix the gas and oil, which can be a royal pain. As for the "best" outboard engines, I can tell you that my best friend and his brother (both of whom are avid fishermen and have their own boats) swear by Johnson engines.

Yamaha will outlast anything else. As a professional I have used many brands for thousands of hours. My last Mercury was a Yamaha with Merc clothing and running gear. Most professionals will choose Yamaha, go to any remote area in the world and you will find mostly Yammies, some very old and few ever serviced. It is not true that 4 strokes are just better than two strokes - the latest Eco-Tec 2 stroke models make more power, use less fuel, require a fraction of the servicing and are lighter and cleaner than a four stroke of the same rated out-put. I find four strokes are ideal for low speed running and at economical cruise of around half to 2/3 throttle, perfect for commercial and all day trolling etc. with little smoke haze to suffocate you - but they will use more fuel than an equivalent 2 stroke at WOT. While the two-stroke has issues with oil passing through into the water it is the unburned fuel that is the big issue with older designs, and that is the single biggest reason 2 strokes have found it so hard to comply with emissions levels. Four stroke sump oil is one of the most toxic things you can come across - as the combustion by-products are concentrated incredibly. Incorrect disposal of used engine oil is one of the biggest pollution hazards of operating four stroke engines. Older two strokes are going to use a fair bit of fuel if you drop the hammer a lot. Older four strokes will be very sluggish in comparison and are very expensive to repair if they have not been serviced correctly or abused. I would look at the whole package and go by the service history and general condition of the boat, including the manual. If you are at the home of a seller look at how they have their shed or workshop set out. If the tools are filthy and lying in random piles all over the shop I would be wary - a well laid out tidy bench and tools will impress me that this owner pays attention and probably looks after all his stuff. A four stroke may blow a little smoke on being started - this is normal and partly a function of low tension ring design but this should clear well within a minute. If when warm you operate the fast idle control (engine not in gear) and let the engine steadily rev at mid idle (3000) for a good thirty seconds to a minute then give the engine a good swift rev to fast idle (4500 plus - don't be stupid) and immediately reduce idle speed - a puff of smoke will indicate worn exhaust valve seals. That will also contribute to smoke on starting if the engine has sat for a few hours or days. If the engine is high hours (4000 plus) that is probably not much of an issue and you may get another 2 or 3 thousand hours of life, but with a low hour engine it points to cold running, like taking off from the ramp without warm up, lack of warm-down running and probably sustained WOT running or other abuse. Again look for reliable service history and caring owners. Anything with a piston will go paff eventually - some just get a lot of help in their demise! And you could also say that Honda have had a lot to do with the demonising of the two stroke - with the same level of investment two -strokes are superior and simpler. Big ship engines are massive two-stroke diesels, because it is the best design for power to weight ratio and cheapest to service. Good luck.

both told you difference...after using 2 strokes im now a 4 stroke fan...but depends on the boat and you......noise..2 s louder...economy...2 s suck more gas and oil...but 4 s cost more ..heavier..bigger boats work well with 4 s mercury is my fave motor company

A point that nobody has raised yet is that it is no longer possible to buy a 2 stroke new,for recreational purposes (thank you EU) so in the future parts may be a problem. Don`t believe the person who states that you can run 4strokes without water - you can,but you will destroy the impeller,as with any other water cooled engine. As for brands,Honda have never made anything other than 4strokes and are very good at it - Yamaha made very good 2strokes and now make equally good 4strokes. In descending order from there - Mercury/Mariner,Suzuki,OMC (Evinrude/Johnson now made in China) Tohatsu (made by Nissan apparently)and then all the also rans. In a lot of cases,with secondhand engines,the condition is more important than the make - if you are not confident,take a mechanic with you,to look at it.

2 stroke engines are cheaper, more powerful, lighter, but like everyone else said they are noisy, stinky, and bad for the water. These are also water cooled. 4 stroke engines are more expensive, bigger, with less power. They are less noisy (but still loud), they don't stink (as bad), and don't pollute the water. They can be run out of the water without overheating because they don't need water too cool them. If you have the money get a 4 stroke. The Mercury brand is very popular. If money is tight look on local classifieds for an old 2 stroke. We have an old 58' Force outboard that still runs like a charm.