Hi,

I just started my first conversion of a Poulon 25cc with a Zama carb.

I'm attaching the pictures from this weekend's activity in the hopes that it helps someone else on their "first", and to provide some context for my questions.



The next pic is of the disassembly of the muffler and pull starter removed.



The next pic shows the length of the drive shaft - it's about 4 inches long. My question is...should I cut it down or leave it and machine the prop hub to match the length? Not sure what plane I'm putting this in so, that may have an impact on the decision.



If anyone can help me on the drive shaft length question I would appreciate it.

Thx.

Scott

Extend the threads on down the shaft with a die. Make or have made a hub to space your prop out from the flywheel a inch or two. Use the nut on the front to hold it together.

Enjoy,

Jim

Hi Scott,
I have one of these that I am converting. I shortened the shaft some, but I am still working on that issue. The rest of the engine is done less the mount plate and muffler decision. Here are some pictures.

Dave

Thanks for the info...I'll look at shortening the shaft a little.

Another couple of questions...

1) the position of the carb seems like it's gonna be difficult to hook up the throttle servo. Has anyone overcome this problem.

2) Dave, it appears that you didn't turn the flywheel down - are you planning on doing this, or are you gonna leave it as it is. Also, are you gonna replace the stock muffler...if so, are you gonna build one or buy one.

I just finished turning mine (actually sanding it with a drill press since I don't have a lathe) Wouldn't recommend that...took forever, but the price was right.



Thanks,

Scott

Hi Scott,
The shaft of the carb can be reversed since a throttle stop isn't needed with a servo. Care must be taken to replace the throttle plate unreversed and locktite the screw. You can't flip the carb because of the pulse port through the manifold. I left the carb stock until after I test run the engine. Since this is a blower it has a large carb already(10mm). This should be enough for a 25cc. I cutoff the hex section of the impeller hub and drilled out the back to allow it to slide further down on the shaft. I cut down the spacer tube also to match. Notice that the exhust port is larger. I trimmed away the small lip in the port accross the top and at the ends. This gives the engine a 75 degree before top dead center port opening. The sharp edges inside the cylinder must be removed after opening a port. The stock muffler will used for basic testing. I will spend the money on a wacker muffler when it is install in a plane. This is one of half a dozen engines that I am working on and I just put a flywheel on that was on the bench for pictures for you. The stock port timing is: intake=66 degrees, exhust=60 degrees, transfer=50 degrees. Wear a mask when cutting the case, because the magnesium alloy produces airborn particulates when filing or grinding it.

Dave

Ok the conversion is coming along ok....

Now, I'm starting to plan for the plane....

Anyone have any recommendations on an airframe to mount my 25CC Poulan in the pics in this thread.

All input welcome.

Thx.

Scott

might look at the Morris Hobbies Balsa Nova 120 it has an 80 inch WS and if you keep the plane at 11 pounds your wingloading is 22oz/in^2 keep it at 10 lbs and your wingloading is at 20oz/in^2 wouldnt be to bad a flyer i think. take a look at it and see if you agree. it is something i have toyed with the idea of getting.