Hey, I havent recieved the new ring yet, but I have got the engines that Combat sent me. He sent 2 short shaft engines and one long shaft engine. I have read that the long shaft engines produce quite a bit of power, so I am going to test it out tomorrow. I measured the exhaust duration, and it was around 140 stock. Since I damaged the gasket and dont have a replacement, I am going to use the three bond. In order to retain the original specs, I ported the exhaust so that without the gasket, the duration remains at 140. Its not a bare bones stock test, but I figue that its close enough. There are many threads already done about the stock performance of this engine. removing the gasket to increase compression probably yeilds marginal gains. I also dont have a backplate gasket, so I used the three bond there as well. Im kinda excited to see what kind of numbers I will get. The test prop will be the 16-6 prop. I cant use my 16-8 cause I had to drill the center hole out to fit another engine that I have.
I am going to charge my camera up to make sure I get a video for you guys. Dont worry, I will edit out any poor camera work.

I test ran the engine this morning. It wasnt too bad for power. I was getting 7400-7500 on the 16-6 apc prop. Again, the only thing different from stock was the carb, muffler, no head gasket and no backplate gasket. It isnt a "bone stock" test, but its close enough. I am uploading the video to youtube as I type this. It takes a long time to upload, cause the video is in HD. I have torn the engine down, and am going to port it some more. I doubt that I will run it again today, but ya never know. The new ring hasnt came yet [&o] I really wish that it didnt take so damn long for stuff to cross the border. I expect it to be here next week. Frank said it usually takes about 10-14 days to get here. Another thing that would help the engine that I tested today, would likely be a new set of rings, but I want to try a few other things first. I also kinda want to get a header bent up for this thing, and try a canister. I would like it if the engine was a bit quieter at WOT.
Another mod I want to try is changing the timing of the transfer ports. In stock configuration, the tops of the transfer ports are level with the top of the exhaust port. When I increase the timing of the exhaust, I think it would further increase power if I also increased the timing of the transfer ports. It will be a b**** to work on them, but I am very interested in this mod.

here is a link to the video. Enjoy.
I have already modified the exhaust again, and im going to run the engine later on http://www.youtube.com/watch?v=THTsSHFXWII

Just got back from testing. Not much improvement. I think that I need to work on the intake. It seemed like something was "holding it back" Im going to search for a good starting point for intake timing. Im also going to try modifying the intake manifold as well.
One thing I thought of doing was cutting grooves in the manifold (kind of like rifling) I think Edelbrock makes a carb spacer for small block engines that incorporates this design. They claim that it improves power by helping the fuel atomize better. I dont know if it will help a 2 stroke as much, but its worth a shot i guess. I have lots of manifolds, so if it doesnt work I can replace it.

You may want to try a velocity stack.

With the Carb. right in the prop wash it's hard to tell
if you have the vapor dancing in front of the Carb. or not.

They can be good for a couple hundred RPM plus it may fatten up your mid-range.

A flat washer and a short piece of pipe makes a velocity stack.

I am going to get a velocity stack made up this week.
I did a little porting on the intake. I increased duration by 10 degrees (I think its at 130 or 140) I have it written down at home. (im at work right now) I did test it again close to dark. it still got the same rpm. When I ported the intake, I also took some material off the top of the port and sides to enlarge it. Unfortunately, I took too much off the top, and now it is barely open when the piston is at BDC. This lets the exhaust escape out of the intake as well as the exhaust. It sprays quite a bit of fuel out when running. I was kinda pissed at myself for doing that. Before I headded in, I took the exhaust off, and the fuel didnt spray out as much, and I also got an increase to 7800 rpm. So Im thinking, cause the jug is pretty much garbage now. I am going to try to increase the exhaust by another 10 to 20 degrees and see what happens.
One thing I noticed on my short shaft cylinder is, the Intake port is slightly larger than the one off the long shaft engine. This could mean better potential for this engine.
So, for monday, Im going to go to a machine shop and see if they can do a couple things for me: Make a velocity stack and Bend up a header pipe, so I can use my home made canister.
I think the canister will help because I built it for a much larger engine, so the backpressure will me minimal.

I recieved the Frank Bowman ring today, and got a chance to test the first engine. Power increased by quite a bit. I was getting a good 7700 rpm with the apc 16-6. I know the ring is still seating, so I didnt really go all out. I would like to increase the duration of the intake, but am afraid of ruining this engine. I guess I could assemble one of the other engines, and try out a few mods. I blueprinted my stihl 25cc the other night, and the exhaust on this engine is about the same as the stihl. The intake is about 10 degrees less duration than the stihl, so I kinda want to change it so that it matches the stihl. Then I will test it, and if I feel it needs more power, then I will look at the transfer ports. I also need that velocity stack, cause there is a bit of fuel spraying out the carb. I think I will make an "el-cheapo" one tomorrow.
I have a small video that im uploading, and will post as soon as its on youtube.

Well, its really late, and I cant really sleep cause Im thinking about the mods to this engine too much.
I just realized that my initial test with this engine was with a JXF 16-8 prop. After the new ring I havent compared it with the same prop or gave you guys any "real world" improvements. Tomorrow, Im going to try the 16-8. I also fixed my muffler. I also added another tube. (i think it was too much back pressure with only one tube)
So far the mods for this engine include:
1) bigger carb (WA19A "27/64" ) 2) made a 1/2" hole in the muffler to increase flow 3) Removed head and backplate gasket and used thinner ones (that three bond stuff doesnt work very well) 4) Increased exhaust port size and timing (by using thinner gasket intake was also affected) the timing is: Intake open 299 degrees Intake closed 62 degrees Exhaust open 107 Exhaust closed 255
Intake duration 123 degrees Exhaust duration 164 5) Frank bowman ring

Now for my question...
I checked the intake duration against my stihl and the POULAN is at 123 and the STIHL is 116. But the stihl intake opens about 7 degrees sooner. Should I advance the timing of the intake any more?
Has anyone ever messed with transfer port timing? If so, how did you measure the duration and if I advance it too far, how will it affect the engine?
thanks alot,
andrew

Here is the short video from today http://www.youtube.com/watch?v=luLYADYo3Ek

I test ran the engine again today. With the 16-8 rpm dropped to 7000. It seems like I lost some torque with the increased duration. Also, the ring needs to seat more. I put the 16-6 back on and ran the engine at about 3500-4000 rpm for about 30 mins. I then tested full throttle again, and rpms were up to 7800. I think most of that improvement was from the exhaust modification. I let the engine run for about an hour total today at low throttle (mainly to keep the heat down) and on my last rpm check, I was getting 7998rpm! I think with a bit more run time, I will have got the 8000 rpm that I want.
I have decided to leave the transfer ports alone, and am going to run the engine as is. I got the target power that I need. Once I can afford it, Im going to order an XYZ CDI for this engine. I think that rpms should increase as well, cause the heavy flywheel wont be holding it back. I also still need to get a header pipe made up, and a velocity stack. That probably wont happen for a week or two.
For now, Im going to modify one of the other cases for EI use and get one of the flywheels center cut out.

When breaking in an engine, it's the heat cycles that break it in.

The heating and then cooling of to the surrounding tempature.

So run the engine to the working Temp. and let it cool.

Anyway that is what some experts say.

Just my $.02 worth

I didnt run it for an hour straight. I ran it for about 10 mins, shut down, let it cool, then started it again. I really wish I had a plane ready for it. It would be much better to break it in in the air. I guess thats this winter's project...
Depending on the day, I might run the engine again tomorrow. I took a different intake manifold, and drilled it out to match the same size as the carb. The other one was just a stock manifold. It might make a bit of a difference.

Hello
see it

http://www.rcuniverse.com/forum/m_30...tm.htm#3082557

an englishman have a link to http://www.rcmf.co.uk/
in this site the men "diablo" (avatar in RCU) convert a Poulan, you must read to find the link, I can not find, also you must be logged in rcmf.uk to see the Poulan conversion, nice to see, new tricks, the better how to balance flywheel (magneto) sorry my english. Do a reading in boths links, is worth.
Also see
http://www.rcuniverse.com/forum/m_31...tm.htm#3192059

for newer Poulan 25.
I come from flying field 2 hours ago and my Poulan reached 63 hours flying time. So sweet .
Happy landings
Jose

Thanks for the links. Im awaiting the approval from the website. It seems that I did go a bit overboard with the exhaust. I also need to advance the timing of the transfer ports. I think I might do that tonight. I would like to turn the case down for more compression, but I dont have a lathe. I do have plenty of power for the project I am going to do, but more never hurt anyone....
If I get the mods done, I might get to run the engine tomorrow. there will be a video, if performance is increased.
One thing I dont really get, is why this thing is a dog with the 16-8. It should have improved. The more I think of it, the more it frustrates me. I dont think I can fit a 16" prop on the plane im going to build, but I would be happy if I could get 7500 or better with the 16-8.

Is there a big difference between the poulans with the bolt on mufflers and the ones with the springs?


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The best results usually come from:

Bowman Ring

Exhaust timing 150 degrees.

Matching the transfer ports between the case and the cylinder.

Opening up the stock muffler. In your case I'd braze a 3/4" tube in place of the existing out let.

A Carb. with 2 mixture screws. 3 or 4 MM bigger at the most. A smaller Carb. will cost you a few RPM but will transition better

Transfer ports are usually pretty good. You might try to square them up, I don't suggest raising them.

Remember more is not always better.

This Poulan thing just hit me, I stopped by my favorite Auto Parts and other things store today for some metric cap screws and the operator ask me if I would be interested in a Poulan Chain saw for parts. "SURE" Well, when we got in the backroom, he unloaded three Poulan Pro saws on me just to get rid of them. A 35, 42 and a 45. The 35 and 42 had an exploded or broken spacer washer in the centrifical clutch, and the 45 had an out of round centrifical clutch housing. There are some other minor problems, but all very fixable. I had the 35 and the 45 running in about an hour, but need some additional work on the 42. It appears to me that these may be a very adapatable conversion engine. What can anyone tell me about them. All are near new. I am a Ryobi nut, but???? Flathead 4

If you need parts, I have a link on my poulan 42cc thread. I dont really have any experience with saw engines, but Im hoping to get into that this winter... If I have time... Im planing on building 2 kits and having another one on the boards by spring. It sounds like I will be living in Northern Ontario this winter, so I will have lots of time...

My fat finger, the 45 is really a 46. It runs and seens to have a lot of snap. The 35 has a broken butterfly arm, and the 42 will be back togather soon. Haven't had a chance to go any further, but after talking to the guy I got them from, he said the engines are good, but the rest of the saw is junk in his opinion. Frank Bowman is sending me rings for a homie 50 that I am setting up for a flying friend. This weekend is "FALL FESTIVAL" in goodyville, so that means the Model T will be out for the auto show. Dang, there goes my weekend again....Flathead 4