Husqvarna 324L String trimmer mods

Always wanted to check out one of those new 4 stroke weed wackers...so, I bought a brand new Husky 324L.  


25cc OHC engine. 1.07hp @ 7000rpm, I saw markings from honda on the underside of the plastic engine cover and the muffler, so aparently they make the engines. It looks fairly decent as far as the castings ect.


A single cam lobe operates the valves.


The rockers/followers are each on a shaft. There's a small internal timing belt running the cam, similar to the honda gc160 and gc190 engines used on pressure washers and things like that. Makes sense if these engines are made by honda.


There's a centrifugal decompression release on the cam, just like some of the bigger lawn mower engines. According to the manual, the muffler has a catalytic converter in it, and also I notice the crank case breather from the valve cover goes to the air box. Looks like there might be some epa stuff to modify a bit here before fire up.... Also before filling with oil, I'd like to check inside the crank case with a camera to make sure there's no metal shavings or anything in there from the factory. Stay tuned for pointless modifications!

Ah, an over-head camshaft engine. Neat! I've never heard of a 4-stroke weed whacker, except for the walk-behind ones. What are you gonna do as far as mods, mr.mod? haha.

4 strokes have been out for awhile, but 2 strokes are still the most common. As far as modifications, I don't think I'm going to do anything too serious. To start with I think I'll replace the factory muffler with a straight pipe. Maybe check the ports to see that they are in good shape without any casting edges. I was thinking of looking into machining the bottom of the jug down a bit to increase compression, but that would slacken the timing belt which I think is just a stretch fit with no tensioner. The carburetor has a plastic throttle which rotates like a ball valve. I think i'll see how it runs and sounds stock first before I hack anything up too bad. Also if something is wrong with it, I want to be able to bring it back to exchange it. Don't think they would be too happy if it came back with a straight pipe. For a tiny engine I think it's fairly high performance already, most of the mods will just be eliminating smog equipment and simple stuff.

Oh ok, I gotcha. I'd love to see the guy's face if you tried to return it with a header pipe and a big velocity stack on it hahaha.

Does it weigh about the same as a 2 stroke?

The entire thing weighs about 11 lbs. I think the difference between this engine and the 2 strokes is negligible, although I didn't compare them. And I was wrong about the cat converter in the muffler, this particular model does not have one, but some do. I looked in the crankcase with the inspection camera we have. I can't get enough angle to see what the rod looks like but I can see there is a couple of steel dippers that are apparently part of the crankshaft or attached to it. There is of course a tiny gear on the crank which the timing belt goes around. Looks clean enough inside, I'll fill it up and break it in a bit then drain it back out. They give you a small bottle of oil to start with and 10w-40 is recommended. I expected thinner oil with such a small engine.

Didn't trust the mini bottle of oil they provided, so I filled up with some Synthetic oil from BMW. Of course that's just made by someone else anyway with a BMW sticker slapped on but, I would guess they have fairly good quality stuff. Also I've got the ATLTF advertisement sign in action in case these pics show up anywhere. Forgot to use it before on the other ones...

The clear plastic hose visible is the crankcase vent from the valve cover. I blocked off the air filter side with a vacuum cap. Later I'll secure the hose better and tuck it in, but this is good enough for a test fire. I figure there's no point in directing dirty crankcase blow-by into my nice clean carb and engine.

Ran a full tank of fuel through today doing some test running. First I got a couple gallons of 92 octane, the first one went in the truck to clear out the hose of any previous low octane stuff, then I filled up a gallon can. I was at my grandfather's doing the test running, so I also got out his 28cc 2-stroke snapper string trimmer for a bit of comparison. The Husqvarna seemed to bog down a bit in thick high weeds, but it did get the job done. The Husqvarna was a lot lighter than the snapper and had less vibration. The Snapper bogged down too when the weeds got thick enough, but it seemed to pull through better.

One thing I noticed was that I had the oil slightly over filled. With such a small engine, I imagine the oil level could have a significant effect on power. Too much oil = more drag on dippers, crank, and rod.

It could be just my imagination, because the husky is so much quieter than a 2 stroke. Being a 4 stroke, it also sounds like it's turning lower rpms at the same engine speed. It could use more power in thick weeds, but over all it's a nice machine and it has a cool sound compared to the conventional 2 cycle trimmer. I'm thinking about how to make a performance exhaust pipe to fit.

After I used a tank of fuel, I changed the oil, filling back up with more BMW 5w-40. I did notice some color in the oil which looked like fine aluminum, but nothing horrible. I expected to see a little bit at first since it's new. I'll change it again after roughly another tank of fuel. Next time I don't think I'll see so much. Then I can wait a while between oil changes.

Cool stuff mr.mod. I would think the Husky would have a bit more torque being that it's a four stroke, but wouldn't rev as high as a two stroke. Hmm, I kinda wanna get one of these now as well! Haha.
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I'd get one just because I get tired of the 2cycle oil.

Maybe the dull lookin aluminum in the oil was just the assembly lube washing out. Maybe a megaphone exhaust, LOL.

prancstaman wrote:

Maybe a megaphone exhaust, LOL.

That would be so cool!

I was actually thinking a small megaphone would sound cool, but I was worried about it being too loud. I'll have to see how loud it is with just a straight pipe.

Rain here today so more testing has to wait...........

Been awhile since I worked on this. But time to take care of the stock muffler issue... The issue being that the muffler is a muffler and it's stock...
First thing is to remove the stock unit for closer examination


The exhaust exits the stock plastic cover here, so I would like to keep it that way when I make my own pipe.


Stock muffler is a tapered fit with no gasket. Our pipe will be the same.


This bolt is close to the correct size diameter. Hard to find the perfect size pipe, so I will make my own.


Some lathe action and drilling the center out on the mill. Welded a washer on for a flange and cut the slots for the studs to fit through.


So far here's where it's at. Need to cut a hole in the bottom of it and weld on the rest of the pipe. The part that sticks out past the washer will be removed later. For now that's just to hold it in a vice while I'm working on it.