Yesterday I was tinkering at my bench with several engines that I have. My goal is to make a conversion to go in my GP Tiger Moth. I had already converted a Ryobi but with the rear carb and exhaust it is too long and I dont want to hack up the firewall. I had been tinkering with a Poulan 18cc but it is too small and the timing is too tame. I have several other Poulan motors laying around and I started looking at them. First I noticed that the 25cc that I had used the exact same crankcase as the 18cc and that the head is almost the exact same size. So I slapped it on my 18cc crankcase and checked the timing on it.

Exhaust 135
Transfer 95
Intake 122

Much more aggressive than the 18cc. And compression seemed pretty good. It has 4 transfer ports but they seem pretty narrow but fairly deep. The piston ring is pinned.

My conclusion was that the 25cc egine may be what I am looking for. I can get an egine mount, prop hub, and velocity stack from wackerengines. What would you all recommend to convert it to electronic ignition?



Thanks
Jim

I have the CH_ignition's CHXL unit on my 25cc Toro. It runs very well.

I also purchased the XYZ unit from www.hobbycity.com.
$25.00 plus $8 for the pickup.
I haven't installed it on anything yet but it does throw a real nice spark.
http://www.hobbycity.com/hobbycity/s...idProduct=6292

There is not suppose to be a need for spark advance on these small engines.
When I set the CG to spec. I had to add a 3 ounce heavy spinner.
And my Tiger Moth needed 4 degrees of down thrust to fly right with the Toro on it.
That's in instead of the 2 1/2 degrees called for.

I don't remember the weight of my Toro Be 2 1/2 pounds comes to mind.

I have a Super Tiger G90 on it now. No weights added and it balances perfect and flies with authority. It does have onboard glow as well. I might just try it with the mag first to see how it goes.

Jim

I moved as much as I could behind the cockpit.
I added a 4 cell 3500ma battery for a flight pack.
Mine balanced perfect according to the book.

I'm re-doing the the muffler.
Extending the stinger, slanting it back at a 45 degree angle and increasing the diameter 1/8th of an inch.

Perhaps this will help keep the plane a little cleaner and build some low end tork.
The stinger didn't extend far enough past the firewall.
I ended up with a lot of black goop on the bottom wing.

This the before picture.

What size tiger moths do you guys have? mine is 1/4 scale 88" ws I'm putting a 28cc weedwacker/poulan on it and it has the rear carb and exhaust it is alittle to long but not to bad. I'll try to post a picture of it.

I forgot this picture.I made my prob hup and threaded the crank shaft and then I cut all the extra shaft off.

Mine is a Great Planes 60 size.

Length: 60" [1,524mm]
Weight: 10.25 lbs [4,592g]
Wingspan: 71" [1,803.4mm]
Wing Area: 1360 sq in [8,840 sq cm]
Wing Loading: 17.35 oz/sq ft [485.5 g/sq cm]
Radio: 4-ch (5 servos)
Engine: .61 two-stroke, .91 four-stroke [10cc 2-stroke, 15cc 4-stroke]

The basic rule is 1200 sq. in. for a weed eater motor and mine flys great with the Toro.

A friend is building the SE5a kit from Dyna Flight and were planing on using the 25cc poulan in it.
It actually has shorter wings than my Tiger Moth.
The Cowl is very narrow so the rear Carb and Exhaust is a perfect fit.

I hope the Poulan performs as well as my Toro does.

I really wanted at least a 31cc for it but until something else comes along I'm going to try the28cc.My wing area is 2,247 sq.in and it calls for a 120 4stroke.I'm still working on the build of mine.I bought it at a auction and all the turn buckels and fixing plates are gone so I have been making all this and as you know it takes alot of time and the plans don't show good pictures of them.
clocknut

I ordered the XYZ CDI ignition from Hobby City yesterday and a prop hub and mouting plate from Wackerengines. The CDI and the Hall sensor shipped was only 39 dollars. Until all the stuff comes in, I'll be waiting for parts.

I also have a Zenoah G20 that I am going to mount in my GP Tiger Moth.

I too have the Dyna flite SE5 about half built. I had a Ryobi that I was going to put in it but I think it is too big. Considering putting the Poulan 25cc in it. Been thinking about making a custom muffler for it from copper water pipe and using a pipe clamp to strap it to the head. Does this sound like a doable idea? That way I'll only have the carb sticking out the side on the SE5 and I'll pipe the exhaust out the bottom.


Jim

Here's a muffler I made for my Katana out of copper pipe, etc. It sounds great and the engine turns over 9000 rpms.

Remember though that it has to be brazed or silver soldered with real silver solder. The Sta-brite silver solder that most people use when they think of silver solder will quickly melt. (Ask me how I know...)

AV8TOR

Guess I am ignorant about the solder. What is the solder that plumbers use to install copper pipe? I did not know there were different kinds. But I can see that you would have to use a solder that could handle some heat.

Jim


BTW, Great looking muffler.

Check with a welding shop and ask for true silver solder or silver braze. Or you can braze the parts with bronze welding rod. The solders used for plumbing, electrical, etc. are low melting temp and won't last 2 minutes on an exhaust system. There is also a silver solder called "Sta-Brite" that has a small percentage of silver in it, but it is also low melting temp and won't work either.

The brazing will require a hotter torch than the common plumbers propane torch as well...

AV8TOR

We have an acetylene torch here in the shop. Will that be hot enough?
I have never used it.
We also have a mig welder too.


Jim

Another question. Does anyone have a suggestion on how to make a spacer for the CDI magnet without a lathe? I do have a drill press and extra flywheels. Could I cut out the center of a flywheel and use it?

Jim

I use a hole saw and cut the center out of the flywheel. It is a little tough to dress it perfectly round with a drill press, but it can be done. Make sure you make it big enough around that it won't split when the prop hub is tightened down against it.

Yes, an acetylene torch will work fine for silver soldering and/or brazing.

AV8TOR

I finally got a message today from United Hobbies that they have shipped the ignition I ordered. Now I need to figure out how to mount it.

I figure the best way to mount the sensor is going to be with a pipe clamp.

Couple of questions.

What size magnet do I need to get? Does it matter which pole is up and how do you tell which pole is which?

Where on the hub do you mount the magnet? It would seem to me that you mount it on the hub at a point that is accessable to the sensor at around 28 degrees BTC. Is this correct?

Thanks
Jim

Jim,
I have a couple of those ignitions on Ryobis, you'll be pleased. I use the 1/8th inch rare earth magnets from Radio Shack. It does matter which way the magnet is mounted. Just hook up your ignition and pass the magnet over the sensor to figure out which way. I mounted the sensor on a hose clamp with some small counter sunk machine screws and self locking nuts. It makes for unlimited adjustments (at least on the Ryobi). As a note the ignition fires just as about half of the magnet has exited from under the sensor. That might help in where you do the final installation. You are correct, just find your TDC and your 28 degrees BTDC and mount the magnet wherever it fits best. Im not sure on the Poulan but on a Ryobi, using a hose clamp it really doesnt matter, you can mount the magnet anywhere and just move your sensor. Just depends on where you can mount the sensor on that Poulan. Hope that helps...............mark

Thanks Mark.

Exactly what I needed to know.

Now if I can just get the ignition here. After I started having trouble with Hobby City not shipping it, I found a US distributor for this ignition and the XYZ engine brand. http://southeastengines.com/ At $55.00 it is still an inexpensive option. That is if it works well. From all I have heard so far, it should.

Jim

Forgot to ask Mark,

What size battery are you using on your XYZ ignitions? Can you post some pictures of your installations?

Jim

Jim,
Im using a 5 cell 2100 mah. There are no instructions with the unit. On the actual ignition box it just says 6 volts. I know alot of the units use 4.8-6V but i didnt try a 4 cell. I'll try to remember to take a picture tonight and post it.

Thanks.

Jim

Can any of you guys tell me if that United Hobbies ignition unit is auto advancing??

Thanks,
AV8TOR

That is a good question. I noticed that the US distributor has been answering posts on the gas engine forum. Lets aske him.

Jim

I wanted the answer to that also so I brought my timing light to the field yesterday but it got too windy so I gave up. I planned on trying the light tonight after work. Hopefully I'll be able to post my results tomorrow.

I posted the question to Ron the US distributor of XYZ engines on the gas forum. In was in a thread labeled XYZ engines.

Jim