Cool. However I found that my Poulan doesn't like to have magneto closer to the flywheel than 0.5mm The magneto support flexes and with the flywheel closer than 0.5mm the magntic force is so strong, that flywheel touches the magneto core. With 0.5mm gap I can't crank the engine by hand fast enough to get a spark. So for me the best option is electronic ignition or glow plug (I hate starters). Because glow plug works great I will play with that for now.

I read in the other thread guy did the whole bunch of calculation for Poulan 25cc. The first thing was increasing compression to 10:1. This was done by shaving 0.5mm from the bottom of the cylinder. I did that and I can fill the compression is stronger.

Then I run the comparision test: before and after increasing compressiion. Motor gaind 140 rpm (APC 17x6). Quite qool. I used the mixture of 40 cc gasoline with Motul (1:33) + 40 cc Methanol + 2cc Castrol oil. This result the fuel: 47.6% Methanol, 46.2% 91 oct gasoline, 6.2% oil (Motul/Castrol mix). It is like 1:16 oil. I wanted it very wet as I don't know how the motor would react to higher compression.

So here is the test: 7160 rpm (7020 witl oryginal compression), easy to start by flipping the prop a few times (this time starts like normal gasoline engine with electronic ignition), 1700-2000 idle. After running idle for about a minute I opened the throttle WOT and engine jumped to high rpm without hesitation.

As a note, I didn't hear any pinging (no nitro used).

After the run I examined internal parts of the engine. I found a lot of oil everywhere. It looks like 1:16 is a little to much. Next time I will try something like 1:25.

Now before I start to modify it more (cut ports) I need to test bigger carburetor. Any suggestions for Walbro 11mm venturi (my Zama C1U is only 8mm venturi) that will be compatibile (mounting holes ) with ZAMA C1U?

BTW I tested also another prop: APC 17x4 - I got 7550 rpm.


RysiuM