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Someone gave me a 52cc string trimmer for free because they say it wasn't working. We would only get it started by dropping a few drops of fuel into the cylinder, and it would idle quite high for a few seconds and die.

So I took apart everything, every single screw, carb, crankcase, ignition, everthing. Cleaned it up, made new gaskets myself with gasket paper (half of the cylinder gasket was nowhere to be found), and put it all back together.

Pulled the string, and it pretty much started at the first try, I adjusted the carb screw (it has only one), the carb looks like this:

enter image description here

I left the screw in a position that if I thighten it more, it idles erradically and if I tighten a little more it starts to die. And if I loose it, it bogs down when giving throttle.

My concern is that, when at WOT, it feels a little scary, like a racing engine. Im quite sure that it's not sucking extra air anywhere because I had that issue on a chainsaw and it would idle very high, this one idles perfectly.

I saw a stihl weedwacker that would barely make noise at full throttle. i know, we can't compare them, the stihl costs like 10x times more money. The one I have is a generic chinese machine, and it does have a sticker that says "114 decibels" so I guess it's supposed to be noise.

Are these cheap 2 stroke engines supposed to feel that powerfull at WOT?

I am not planning on spending much money on it, got it for free and just working on it for fun, but could something be causing it to rev too high at wot? Or is that normal? Everything else seems to work perfectly, starts easily, idles fine, great throttle response, it just feels like it has too much power. I am using a 32:1 fuel mix (that's what the box it came in says should be used).

  • How long are you letting it idle and warm before testing throttle response? With my blower and chainsaw (which have almost exactly the same carb) it takes ~30 seconds - 1.5 minutes (depending on ambient temp) to warm before throttle response is stabilized. However the idle setting shouldn’t really affect max RPM at WOT. From my understanding (feel free to correct me if I’m wrong) that’s primarily limited by motor and carb design. If you’re sure everything is clean and rebuilt properly, then it should run as intended. That said, make sure the choke is also properly operating. – kyle_engineer Feb 16 '18 at 5:08
  • BTW the point of mentioning warm-up time is that if you’re not getting it fully warm when calibrating the idle, then you may set it a bit higher than needed. All my 2-stroke equipment will bog/die with too much throttle before it’s warm, but they run perfectly once it is fully warm. Again though it don’t think that would particularly affect WOT revving. Unless you’re also leaving the choke completely closes then maybe it would... – kyle_engineer Feb 16 '18 at 5:12
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Are these cheap 2 stroke engines supposed to feel that powerful at WOT?

Short answer: Yes.

Engines have power bands, a point in the power curve where the engine has peak power and torque. The power band for two-stroke engines is typically in the higher RPMs. So, it is not uncommon to notice power peaks at WOT.

Because there is little power/torque at lower RPMs, on these small two-stroke engines for weed trimmers, it needs to run at higher RPM to achieve the power to trim heavy grass and weeds.

Most of my two-stroke experience is riding off-road motorcycles. I describe hitting the power band like when turbo boost kicks in.

In this video, the bike in front of the camera is a two-stroke, while the camera bike is a four-stroke. When the two-stroke hits its powerband, it takes off.

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