2 cycle or 4

I’m looking to buy a new weed wacker/trimmer. I am seeing both 2 cycle and 4 cycle. Any thoughts on an advantage of one over the other, aside from the fact that the four runs on straight gas as opposed to an oil/gas mix?

2 strokes generally make more power per lb so I would expect a 4 stroke to be heavier. You should not let mixed gas sit for months at a time because the lubricant will break down. Mix what you need as you go.

I would imagine the switch to 4 strokes has more to do with pollution than anything else.

Dunno about weed whackers, but many lawnmowers, outboard motors and sometimes chainsaws which are two-strokes have a postmix system, in which you have separate tanks for gasoline and oil; these are mixed automatically when the engine runs.

Two-strokes are mechanically simpler - no valve gear to get out of whack. Thanks to Magiver though, I’d better drain down my little Huskie before I use it and pour away the odd pint of pre-mix I’ve had sitting around for a while.

4-stroke: more efficient. Quieter.

2-stroke: more reliable. Louder. Offers more power and RPM, but the 4-stroke is probably geared to get the parts spinning just as fast.
Generally, no matter how you set up a 4-stroke, the 2-stroke is gonna be quick to jump up in RPM…it’s power curve is steep, because it’s making power on every stroke down, whereas a 4-stroke is making power on every other stroke down.

The four stroke will be most appreciated for the smoothness (your hands/arm will thank you) and it’s quietness (it’s relatively quiet vs a 2-stroker). You will see some good mileage gains.
Note: most decent 2-cycle premix oils have fuel stabilizers that extend the life of gasoline. I’d be surprised if you bought a decent brand that didn’t. They are easy to find.

Generally speaking, a two-stroke engine is roughly twice as powerful and roughly half the weight of a four stroke, a 25CC two stroke would be the equivalent of a 50CC four stroke, it’s also a lot buzzier and has more felt vibration

the blue smoke of pre-mix really is only visible for the first couple minutes or so while the engine reaches operating temperature (or when the tool is under very heavy load)

a four stroke is quieter (lower frequency exhaust, 2 strokes have a characteristic high frequency exhaust), and pollutes less, but is heavier

2 stroke; fires on every upward stroke of the piston
4 stroke; fires on every other upward stroke of the piston

I have a 4-stroke weed whacker that I’m very happy with. No mixing gas and oil was my big motivation for buying it. It runs smooth and isn’t particularly heavy.

I think what you have to look at is how it will be used. If you use the tool for a living then weight is a big deal. If you’re spending 30 minutes trimming the yard then the extra weight isn’t as big a deal.

I don’t think you can get a 2 stroke lawn mower any more. I would love a premixer but none of my 2 strokes have it and none of them are dying so I can’t even window shop. In fact, I rarely use my gas weeder anymore because I have a B&D battery powered one that I bought as a set and it works for my small lot (It came with 3 batteries and a 3 battery wall charger).

For a weed wacker I’d go with a 2 stroke. They are lighter and the exposed string/blade is loud enough on its own that I don’t consider the added noise to be an issue.

On a lawnmower where i don’t have to carry the weight and its blade is encased I’d rather have a 4.

I don’t have any 2 cycles that use a post mix system and wasn’t aware of tools that offered that option. If I shop a machine in the future its certainly look for it.

After fighting with gas powered weedwhackers for years I finally bought a battery powered one. I will NEVER go back to gasoline. Unless you’ve got a huge area to whack, those battery ones are great - NO maintenance, and last for years, and starts every time at the flick of a switch! Wonderful!

I vote you should choose on the basis that 2 stroke gives high power plus light weight, while 4 stroke avoids the inconvenience of stocking and adding the special oil to the gasoline. If these issues aren’t important enough, choose on the basis of other differences between the products you are considering.

I have a few 2 stroke appliances including a nice powerful backpack blower and a hedge trimmer, and they have been convenient and pretty reliable. I have some 4 stroke items like a leaf vac and a lawnmower, and they are OK too, but none of them are supposed to be carried. I have an electric weed trimmer, and I find fooling with the cord and moving it from area to area more trouble than using fuel and starting engines.

If you’re not going to properly maintain your gas motors (I don’t), at least run all the gas out of them before they’re put away for the winter. Or if you’re going to leave gas in them, put some Sta-Bil in the tank and run the motor for a few minutes.

Well… 4 stroke trimmers are a relatively new thing. Their advantages are that you only have to keep one sort of gasoline and oil on hand- that which you probably already use in your 4 cycle lawnmower.

The drawbacks are generally greater weight for the same power- you have the overhead of the valvetrain, oil pan, etc… that you don’t really have on a 2 cycle, as well as having half as many power strokes per unit of time.

I won’t speak to reliability… 4 cycle lawnmowers seem to run forever, while 2 cycle trimmers and chainsaws frequently have balky carburetors and need more adjustments. I don’t know if this holds true for 4 cycle trimmers though.

Lower emissions is the primary reason for the move to 4-cycle small engines though. Modern 2 cycle engines hardly smoke, and don’t stink the place up like they did 10-15 years ago, but they’re still drastically worse on emissions, due to the nature of the 2-stroke engine. Every stroke expels a small amount of unburned gas/oil vapor, and you have the usual emissions caused from burning gas and oil anyway.

The one that got me though was expense. My Ryobi SS30 was something like $90 on sale a couple of years ago, but the equivalent Ryobi 4-cycle trimmer is something like $170. I couldn’t make myself pay almost twice as much for something that seemed like more of a curiosity than anything else. I figure I’ll let the kinks get worked out of the small 4 cycles and then buy one when my current trimmer dies.

I actually got my gas trimmer because I wanted the hedge-trimmer attachment, the edger attachment and the leaf blower attachment- rather than have several machines, or several batteries to allow me to do it all in one day, I chose the 2 cycle gas trimmer, because I could do it all without worrying about extension cords, batteries or dealing with separate edger, leaf blower, trimmer and hedge trimmer.

For motorcycles 2 stroke engines don’t last as long since they don’t have a dedicated system for lubrication like 4 strokes do. I would think that also applies to trimmers.