worst consumer product

I use a string trimmer to edge the lawn, but it's electric, and my total grass is perhaps 15' in diameter :-) ...Jim Thompson

So one of these might be a bit of overkill?

Very unlikely, 4 stroke engines are capable of much higher compression ratios, thus yielding more power. Just the same the speed vs power curves are much different between the twain.

?-)

I beg to differ somewhat. The increased compression doesn't necessarily deliver more horsepower. The Stihl 4-MIX weed whacker engine is essentially a 2 stroke engine modified to operate with a 4 stroke cycle with the addition of valves to replace the ports. Otherwise, it's the same basic engine. The 4 stroke probably does have a higher compression ratio, but there are detrimental side effects. The drag produced by having to compress the valve springs is substantial on such a small engine, negating some of the benefits in horsepower. The Stihl engine requires a compression release system in order to get it started. With a higher compression ratio the oxides of nitrogen pollution limit might be exceeded, which is the primary purpose of the engine change.

I can't find the torque/hp/RPM curves for the Stihl 4-MIX engine. Since it's a single RPM engine, I'll guess(tm) that the power peak occurs at the operating RPM and then flattens out when the valves float.

I jut wait till the first freeze, and rake them up. Some years. Some years I don't even mow the grass, since it makes people believe that I'm even crazier. ;-)

When i lived in Ohio I dug around the sidewalks and put down about 4" wide, eight inch deep strip of sand. What few weeds did try to grow, came out with a rake.

curves

Sounds like a bad design. Look up the curves for general designs.

?-)

Edging isn't so much to eliminate weeds as to keep a neat edge so the grass isn't wandering out on the concrete. In my AL house, the Zoysia is so dense the weeds gave up trying. Here, the weeds are so dense the grass gave up trying. :-(

Part of my driveway is covered in grass. When i lived about 20 miles south, you could grow a little grass, but had to constantly fight with cactus.

So, you have a full yard of dimbulb choking out the grass?

See?!

That must hurt.

Looks that bad, anyway.

We have no driveway and no grass. I like that. I hated cutting grass.

You don't need grass.

Isn't it legal there now?

Right. It serves no function.

--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com

Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation

Only to prevent soil erosion.

That's why they smoked his yard?

Maybe. A flat power curve is very desireable on a chain saw or weed whacker. If the curve continued upwards, the engine might fly apart. If it went downwards, as in the typical 4-cycle engine, the engine would only be useful over a narrow range of RPM's.

Using the valve springs to limit the upper end RPM on an engine is not very common, but I've seen it done on small auto engines. VW does something similar on the old bug engines by having the valve stems blend at high RPM. That makes the valves open less, causing the engine to take in less fuel, and creating some back pressure in the exhaust system. The net result is a flat power curve. Floating springs will have similar results, except with a slightly weaker intake spring, causes the valves to stay open longer, causing a drop in compression (and burning the valve seats if maintained for very long). Anyway, it's my astute guess(tm) that the manufacturers would add some method of limiting the upper end RPM, which is probably not a governor.

Dunno about the Stihl, but Honda publishes torque curves for their small 4-cycle engines.

For example, here is the GC 190 model used my pressure washer:

(Click on "Performance Curve").

Best regards, Spehro Pefhany

That's a low RPM design. These Honda 4-stroke engines are closer to what might be found in a weed whacker or chain saw: Note the peak in the power curve at the operating RPM.