I have a new Poulan 25cc out of a leaf blower I am considering putting on a 90 size ultimate. Are these engines supposed to have low compression when you turn the prop over by hand? It runs great and seems to have plenty of power. I can start it with a standard tower hobbies electric starter.

Acam,
Trimmer engines have mild compression. This provides easiler starting and runs cooler in a trimmer shell with flywheel fan type cooling. The rings on a new engine will take a while to seat for max compression.

Dave

Thanks for the info, Since they have mild compression,are they not a good candidate for a performance plane? My cowl has limited space and this engine barely fits.If I go bigger then I will need to do major cowl mods. Do you reccomend another engine in the 25cc range with better power to weight performance? I have been hitting the saw shops and there are a ton of trimmers and blowers to choose from (most are free). I would rather convert my own instead of buying a new engine because the gas engines designed specificly for planes are rediculously high.

.

The trimmer engines can be OK. I have done a few Poulan engines, 42cc down to 25 I think. The 42 was from a Craftsman saw. Decent power but the trimmer engine was not too good. It would do OK in your plane but may be a little low on power due to the wing area I am thinking. I have done many saw engines and the Echos so far are my favorite. Echo blowers have almost the same power for the ones I have done. I have a 23.6 in an Eindecker 90 and it does very well. The Toro 25 is a screamer but the plug sticks straight down and may be an issue for you. Search for Echo and see from there. Also search for Homelite Powerstroke. I know someone who did one of those saw engines and it is very strong.

I got an Echo pb400 backpack blower yesterday. It looked real promising until I ran it when I got home. The rear bearing crapped out and a piece got on top of the piston and broke the top ring. It is a 40 something cc. I can't find any info on it. This one has points on the backside and a small flywheel up front.

Hi Acam,
What Ulimate are you going to use? The CG Ultimate has 54" span and 980 square inches area. One of the guys put a homelite 25 in one. It is a four pound motor. A trimmer engine has a poor power to weight ratio, so it can't be considered high performance. Most of the best performers use electronic ignition to save weight. I plan to put a Mac 21cc on EI in my CG Ultimate. It should come out at 1.5 pounds per square foot for a ten pound airplane. You can do a search for the Homey powered Ultimate in the conversion forum. Here is a picture of it.

Dave

Davewallace, I plan on putting a gasser on a Direct Connection Ultimate. It has a 56" wing. I just got an almost new MCculloch 32cc blower engine today. Free of course. This engine looks very promising. I put a prop on it and test run it on the bench and with the right carb and muffler I believe this engine will do just fine. Do you think this engine would be worth spending the money for the mods? I would even consider going EI. I keep trying to upload a pic but something must be wrong with the RCU site. I will try later.

here is a pic of the MAC 32. The only thing I did to it was put a prop on it.

HI,
The Mac 32 will put good power, but you need to get rid of some of the weight and put an 11mm carb on it. Here is a 32 conversion by Scott at Brillelli engines.

Dave

I have a Poulan 25cc from a leaf blower and I can tell you the engine has very good potential. The exhaust is extremely restrictive because the exhaust port has a lip on the I.D. that
reduces the effective area by 50%. With the stock porting, carb and muffer, the engine tacked only 6600RPM with a MAS 16-8 Classic prop. I added a Tatone muffler, a larger carb and
removed the internal lip in the exhaust port (I filed it open to match the rest of the exhaust port) and the RPM jumped to over 8000. There is room to open the exhaust port a bit more, plus you can open the intake port (it narrows down from the outside of the cylinder where it mates to the carb heat isolator, to a smaller opening as it enters the cylinder. File it open to be uniform in diameter the whole length. An even larger carb than I used could be added and. I'll bet the engine could get close to 9000 RPM with the 16-8 prop after it is broken in.

By the way, this engine is currently listed FOR SALE in the "Gas Engine" section at $ 75.00 with free shipping within the USA.

Good luck,
Mike

I just got finished doing a 25cc Poulan, do you have any pictures to show what you did to the exhaust port?

Remove the muffler and look into the exhaust. The internal lip will be very obvious. It completely circles the inside of the port. Just carefully file the lip away. File until you open it up the the surrounding port sides. Do not raise or lower the main port passage way...only opening it up by removing the lip.

Mike

My exhaust port is tapered but does not seem to have any type of lip. The bottom of the port is level with the top of the piston with the piston all the way down. No lip.
It's hard to see in these pictures but here are two with piston up and piston down.

acam,
It looks like you got the high performance model. With the lip the exhust opens at about 60 degrees before bottom dead center. without the lip it opens at about 70 degrees BBDC. You also get the large transfer passages and intake. My 25cc has a 10mm Zama carb, which is fine.

Dave

I just measured as best as I could with a protractor and a flash light. It is pretty much exactly 70 deg before bottom dead center. I need to get a prop on it in the next few days and see how it runs.