Homelite 25cc porting

Having done a little work on small 2-stroke gassers in the past (go-karts and mini bikes), I know it takes more than simple porting to achieve a significant power gain. Timing, carb CFM, and compression must also be factored in. If you need more power, why not simply buy a larger or more powerful engine from the manufacturer?

Add to that a bigger carburetor and a tuned pipe and you might have the power you need, but keep in mind that the Homelite is a low-end engine with a cantilever crank and a stamped steel rod, so too much power boost and BAG!!! Check on the power boat newsgroups for tuned pipes for Homelites. Several are available. Also, there's a guy on RCU that's selling Walbro carbs cheap.

Yes, I'm aware of all that. I believe I have all that under control. I'm not going for a massive power increase or radical modifications, otherwise I'd just throw down the money for a specialised engine (not naming brands).

A matter of budget and a challenge. It's been done before and proven to be successful. I'm trying to do the same albeit with some care.

I've got the timing details, got the compression details, but haven't any clear details on porting (at least that I'd trust on blind faith). Hence, I'm looking for some more detail to help me out.

"Ed Cregger" wrote in message news: snipped-for-privacy@enews3.newsguy.com...

Agreed, accept those parts are not readily available where I am and getting them from elesewhere is costly and takes away half the fun of doing it myself.

Which I have. The ZAMA model fitted standard to my model is the largest that will fit (suits a 50cc).

That's the next challenge but one I'm ready for.

They have quite a reputation for the boat guys and are making inroads into aircraft.

The quality must be good, even Ryobi are putting their name to them and few people knock the Ryobi conversions.

Having pulled it apart, I see nothing cheap or nasty in it's manufacture that would preclude it from aviation use. In fact, I am rather impressed with it.

Care to describe what you mean by cantilever crank?

My crank is fully ballraced and laid out in a near identical fashion to that of R/C aircraft engines.

Mine has a solid alloy rod, bearings at both ends. I agree that stamped steel stuff is rubbish and not something I would be putting in the air.

I have checked many boat site (not newsgroups yet) but many are pedalling their own product without much advice for the home enthusiast. Those which do give advice are rather vague.

I appreciate the concern about the risks associated with modifying engines for non-standard applications but I did enough research to find this is a safe conversion. Given the price of the motor, some basic machine work, and some help from others it's an excellent project with little chance of failure.

I'm not after extreme limit power, just a mild boost to ensure I have sufficient flexibility.

Check around and see if you can find someone with a book by Gordon Jennings called "Two Stroke Tuners Handbook" It is long out of print but I bet a few hard-core roadracers from the '70s still have one in their toolbox.

I had that book and made the mistake of loaning it out. It has never to be seen again. It is invaluable. I even scour eBay and other places now and then in an effort to obtain another copy.

The really good thing about porting common utility engines is that replacement parts are abundant and inexpensive. So, if one decides that they made a mistake, rectifying said mistake is not a problem.

I would look into getting replacement jugs and pistons of the larger size to boot (30cc). I doubt that they will cost any more than the 25cc parts. I wonder if the connecting rod is the same? I never checked.

Ed Cregger

Yea, seemed like EVERYONE had a copy in the '70s when I was racing. Always used it for my tuned pipe design work.