Honda GX25 OHC, NEW (WITH PICS )
I bought a GX25 yesterday. I haven't done any actual "converting" yet since no one makes parts for it to my knowledge. I am happy to report though, that it runs superb ! the Carburation was my biggest concern on the GX22 and 31, since they seemed too lean........all the time. The new carb with the accelerator pump made a world of difference. Honda claims you get 2-stroke like throttle response due to the new carb, and the lighter flywheel, and I believe them, This thing Rips ! You can snap the throttle full open from a very low idle, and it never quits, It just winds up, instantly. I had a GX22 there too, with both of them fully warmed up and running for comparison. The GX22 requires choke for a long time after start up, and takes a few min before it will idle reliably, even when warmed up, you can never snap the throttle open, you have to slowly accelerate it above idle, then you can open the throttle quicky. The GX25 starts easy, and idles well, even when cold, you can turn the choke off immediately after starting. Now granted, throttle response isn't nearly as critical on an airplane as say... a chainsaw, but I never got the feeling that it was starving for fuel, It always did what you asked, no stumbling, no hesitation, I just hope it's that good under a load too. The GX22 stumbles and hesitates even under no load if you open the throttle instantly. The engine looks better too, The flywheel housing is a casting that will require grinding, but it's not much, just attached with a few "spokes" that are thin, and can be cut through easily. The oil reservoir is still the round drum, but a smaller diameter, and wider, looks to be about the same capacity, just a different shape. The new cylinder with the timing belt channel molded in it will get a double take from engine gurus. As well as the new valve cover with it's bump for the cam gear. The spark plug is in the front, so the plug wire is only about an inch long, looks neat and tidy.
I did get a few weights. I didn't weigh it right out of the box (empty) But out of the box, plus oil, it weighed 100 oz or 6.25 lbs, they claim 6.1 lbs, I'm not sure how much weight the oil adds, but that is pretty close.
With the shrouds removed, pull starter, muffler, fuel tank and flywheel housing (just the part that un-bolts) I showed 72 oz, again full of oil. I ran it like that, so it was a fully functioning engine, with as much removed as I could, with wrenches, (no grinding)
The flywheel weighs 9.8 oz.
I was at 4.5 lbs, I think with some grinding of the fins (a few are much too large, to help seal against the shrouds for baffling), the typical grinding on the flywheel, and grinding away at the backside of the flywheel housing, removal of the pull start dogs, it might be 4lbs. As far as conversion engines go, I guess thats not too bad, It runs like a top, It sounds very convincing, Revs high, nearly instant throttle response, I hope that's indicative of it's power output, I can't wait to get a prop on it. I'm pretty excited, I love the concept, and the looks, I need to find a suitable prop hub before I go any further. The honda flywheels are recessed, so the hub needs a cone shape, to fit down in there, and thread onto the shaft. There is barely enough room for the flywheel nut, a prop hub could be a challenge. I wonder if the ones for the GX31 will fit this new flywheel?