Eagle Flyer

My Feedback: (84)

I recently obtained some Poulan 42cc engines, almost new if not new. I have never done any port work but have every thing needed to do so. I was wondering if any one has done such a thing? And what can be gained. I would do a search but for some reason I can never find what I am looking for.
Thanks in advance.

Scota4570

Having messed with ports I have come to the conclusion that it would be best to leave well enough alone. Add a 15mm carb, open exhaust and good ignition and see what you get. Compare those numbers to other engines of that size and judge the result. That engine is pretty well respected. I doubt big improvents can be made. On the other hand since you have several sacrificing one may not bother you. Down load a copy of the two stroke tuners guide. Read it several times and get real confused, then go fly. IF you need big power in a small package get a DA-50.

rangerfredbob

My Feedback: (13)

check the stock port timing, optimal for our use is about 150 degrees exhaust duration, which is the only port that will show much change in power

Eagle Flyer

My Feedback: (84)

OK, thanks
I also have a used one with good every thing except the ring gap is .011! Will make a good one to do some Frankenstien work on. Getting some rings from Frank to test.

Scota4570

This might be of some use. I forget where I got it, I take not credit for putting it together. See attached image.

Keep in mind that you can change the port timing for higher top end but you may sacrifice a stable low end or smooth acceleration. Sometimes the wide open exhaust duratiation numbers are for a tuned pipe. That will give more time for the pulse to come back into the jug. Things like how the gasses flow and their interia have to be consitered. If you do make a port wider be sure and avoid making the top and bottom flat. You can catch the ring if you make it too wide and don't make it eliptical. Gringind on the ports disturbs the nickasil liner and you might have it flake off. Polishing ports all mirror shiny is not as good an idea as it souds, it can do harm. It is all vey confusing to me. I was able to get respectable number out of a Featherlite weedeater this way. Later I went too far and messed it up. That is the problem for me, "too far" if an invisible cliff. Oh, throwing the jug gasket away alters port timing. That may do more harm than the increased compression gains.

av8tor1977

My Feedback: (6)

That's a handy chart that I have looked at numerous times in the past. If I remember right, my Poulan 42cc had exhaust timing that was a touch low. I raised it to 150 degrees. The engine ran strong with a 15mm carb and a free breathing exhaust, along with the exhaust port timing change. If I remember right, it turned an 18 x 8 at 8500 rpms. A 20 x 8 or 10 would probably be a better prop for it.

Just out of curiousity, does anyone have any stock timing numbers for the Zenoah G-26, and/or any of the DLE engines???

AV8TOR

Eagle Flyer

My Feedback: (84)

I got the 2 cycle manual but haven't looked into it yet. Noticed that several engines in that chart show the same timing before and after for total port time. Is that just a norm or is it that things work better that way?

rangerfredbob

My Feedback: (13)

that's just how it works, think about the piston moving at TDC and BDC, if it opens at a certain angle before it'll close at the same angle after.

Eagle Flyer

My Feedback: (84)

I should have figured that out!!!! Had 4 cycle camshaft stuck in my head. Built a jig to hold the cylinder if needed. Also working on a similiar unit if I should need to reach down inside it. Though at this time I have no idea why. But figured I would do it as long as I was at it.

Eagle Flyer

My Feedback: (84)

Checked a couple engines. A standard one had, 142 degrees duration on the intake and 160 on the exhaust. A low emissions unit had 138 degrees on both.