I was just curious if you get a power increase if you convert a trimmer engine to cdi? I have a ryobi that I want to convert and was wondering. It is side inlet and side exhaust and 25 cc.</p>

There's no measurable power difference

But battery powered ignition engines can be hand started

And idle better.

Depends on the engine. Some engines respond well to having the timing more advanced than the original magneto. It is much easier to optimize the timing using EI, and if the engine likes a timing different than the mag had, you will see an increase in power. I don't use magnetos on any of my many flying gas conversions.

My brother has a plane with a Ryobi on EI. The plane needed a good bit of weight added in front to balance. I said "Well, we can always put the magneto back on it for weight." He said "NO WAY, Real model airplane engines don't have ugly magnetos!!"

AV8TOR

Didn't (don't) REAL airplanes use MAGNETOS? I remember the "mag 1 check, Mag 2 check" from the old movies. Or do I have revisionist memories? :-)

You are absolutely right. On most engines you set the rpms to 1700, then do your mag check. Anything more than about a 50 rpm difference in drop between magnetos is suspect....

AV8TOR

Some engines lose the ability to idle at lower speeds without the flywheel. I believe it may because of balance. You may want to check out the idle before you cut up any parts. I have no experience with a 25 cc RYOBI, but some of the earlier 31 cc engines are next to inpossible to balance if all the flywheel is removed. Practice makes perfect! I THINK. Flathead

Some of the Ryobi 31cc engines use the flywheel to aid in balancing the engine, some do not. (Don't ask me how I know...) One way to find out would be to check the flywheel on a balancer. If it is really WAY out of whack, then the flywheel is helping the crank counterweight to balance the engine. I believe it was only the old engines that used this method.

AV8TOR

On that engine you can expect no noticeable gain by going to EI. It will be easier to start and you will be able to move weight that would otherwise be hanging right off the nose. Thats the upside. On the negative you will have to maintain the ing. battery and then theres the added expence.