Hello everyone, I'm not actually working on an RC project, but I thought you guys could help. I'm wondering if someone can tell me what the lightest weight small 2 cycle conversion engine might be? I'm actually building a backpack generator, but I'm looking for the same kind of power you might find in a model plane.

Any of the weedies can be made light by a lot of cutting,ect.The only problem is that the pull starter and clutch are the heavier parts that youll need plus youll need the housing all in tack to hold the generator head.You wont gain anything at all.Just go to honda and buy the little camping one they sell.Its like 750 watts or somthing.Check out the internet for used from auctions and clearance houses.Make an L shaped frame from wood and 2 dufffle bag straps and your done.[I would preferably just use a gas weedie instead of using an electric one with a generator attached to my back.

A Honda generator is totally different, way overpriced, and WAY bigger than what I'm doing. Obviously the engine is going to be from a peice of garden equipment...but which one is usually they lightest? Just browsing at Home Depot today I saw a 26cc Homelite, 30cc Ryobi, then there's Mcculloch, Poulan, etc...which ones usually turn out lightest? There are dozens to choose from...

A Homelite 25-30cc will weigh in at just around 2Kg with a machined flywheel, pitts muffler, carb, and custom mounting setup (which includes a machined 'stuffed' backplate).

A Ryobi 31cc using the same carb and pits muffler, with machined flywheel, will come it a little heavier. Not sure the exact amount other than a friend and I both did our conversions at the same time and his scales showed the Homelite to be lighter.

Having said that, the Ryobi has a smaller crankcase and is much easier to convert.

Powerwise (25H vs 31R), both will be similar with a WA-167 carb. If you go for the 30cc Homelite the peak RPM is lower, which I attributed to radically revised exhaust port timing (compared to the 25cc). Of course, different markets apparently get different porting (going by my web-research).

If weigh savings are a major criteria, it's best to buy one of the small Chinese gasser engines. They will weigh roughly half a Kg less and come with electronic ignition and much more power (relatively speaking).

in stock form with magneto and fan housing, they're all going to be in the 5 to 6 lb range. The new ryobi 30cc engines are the same as a homelite 30cc, and I think the McCulloch 31cc trimmers are a Ryobi 31cc (I don't know what the heck is up with that). so since you aren't ripping off a lot of the stuff that adds weight when comparing these converted to airplane use, you aren't going to notice much of a difference looking at them as a complete power head.

myself I would go with the ryobi 30cc, I have both a homelite 30cc and a ryobi 31cc weedeater, with the same cutting attachment (they both have the quick change thing) the 30cc has more power

The Echo engines have the most power to weight in my experience, but they are expensive to buy!

AV8TOR

I'm leaning towards the Homelite 26cc because they're only $69 in a weedwacker at Home Depot. I will be removing everything I can from the engine just like a plane, with electronic ignition, etc. The generator will also funtion as a starter.

Is there a major difference between the newer 26cc engines, and the 25cc Homelites? Can I buy things like cylinder jugs, rings, bearings, etc for the motor?

I'll probably try and increase the compression ratio and run E85 for a better power to weight ratio.

keep in mind that the flywheel also acts as a cooling fan for the cylinder head, which in a stationary application is necessary, in a plane where a propeller is placed directly in front of the cooling fins, this is not an issue at all...

at most you might loose a couple ounces using electric ignition, a flywheel and magneto weigh about a pound, if you add up the weight of an ignition module and battery needed to run it (a standard reciever type battery is supposed to last around an hour of run time), you're 3/4 or so of the weight of the flywheel and coil... the magneto is kind of like free ignition, and if you had to custom make some kind of cooling fan, that's a lot more trouble than it's worth...

Your probably better off using magneto ignition instead of electronic. Considering the runtime per battery charge, you will have to find some way to charge the ignition battery. That means that your backpack will also include a battery charger of some sort. Using the generator as a starter does away with the main advantage of the electronic ignition ie. easy starting.

I have a small stationary generator powered by a Quadra 35. 400 watts. Generator is about the size of a car alternator. Whole thing weighs about 15 lbs. There is a small airvane in the blower housing connected to the carb. It's a governor to keep it at a constant 115 volts, no matter what load is on it. Muffler is about 4 times the size of the stock Quad muffler.