Jan Ridders Puppy Build- Help!

[Stu_NY]

I have completed my version of Jan Ridders 2 stroke design and could use some help getting it running! This is my first engine build so still trying to ramp up.
I adjusted his plans to use materials I already had and converted to inches but maintained all the critical dimensions- piston/bore/ports etc.

So after my first attempts to start got not even a pop (using drill to spin), I discovered that in fact 25 year old coleman fuel does go bad oh:

With a new bottle of fuel in hand I now can get the engine to pop along nicely with the drill attached, but won't run once I remove.

I took apart the engine and checked compression and port openings/timing and all seem to be working as i think they should.

I am using both an RCEXL CDI ignition, and a homebuilt version with a coil and both give exact same result so I am ruling out ignition problems. Timing I think I have right- i adjusted until I get the most consistent popping and it is pretty much at the recommended 28d before TDC for the CDI unit.

So where do you guys start when facing this? Any usual or likely culprits?

My best guesses now are:
Starved for fuel? Maybe suction stroke under piston not sufficient to pull enough fuel into engine?
One way valve neoprene ball bouncing around too much? Or not enough so blocking fuel intake?
Not enough space at head of cylinder- seems pretty tight up there- maybe too much compression if that is even possible?

The piston and cylinder are both CI and were lapped together so seem to be very good fit, and create lots of suction when I move them.

Appreciate any help!!!

Here is his page describing the engine:
http://ridders.nu/Webpaginas/pagina_tweetakt_puppy/tweetakt_puppy_frameset.htm

 

[Mechanicboy]

Since the engine is ringless, is the fit between piston and cylinder tight enough to keep compression?

 

[Stu_NY]

Yes, if I just pull the piston either way in the cylinder with palm on other end and the ports covered it sucks my skin and holds it. Not scientific but seems to be adequate? I lapped them to each other so should be pretty tight in any event!

 

[Mechanicboy]

Ok, use clean gasoline or coleman fuel. The important you check, is it enough vacuum to suck fuel gas into engine from fuel tank. And the ignition timing is set to about 2-8 degree before TDC.

The ball valve must be tight then you can listen the exhaust say "poof" each time transfer port is opened by piston.

 

[Stu_NY]

Thanks Jens, I can hear the "poof", but how do I know if I am getting fuel all the way to the cylinder vs. just air making the "poof"? I will work on this area more... hopefully get it going on it's own soon- thanks for the help!
Stuart

 

[Cogsy]

If it's popping along consistently I would hazard a guess that it is a fuel issue. I'm not overly familiar with the vapour type carb setups but don't they have a mixture adjustment? I'd twiddle that and keep trying it at various settings. Sounds like it's very close to running already. Good luck.

 

[Stu_NY]

Thanks Al, yes it has a slide over a slot in the tube that feeds fuel to the cylinder. Now that you mention it, I find that it only pops with the hole completely covered which may indicate that air is getting in somewhere else in the line or I am not getting enough suction to pull a large amount of fuel in.... plenty to investigate- thanks!

 

[Mechanicboy]

When the engine sucks air into the fuel tank, it will form waves in gasoline so it is formed vapors and supplied into the engine. In a cold room can be difficult to start the engine because gasoline is less volatile in lower temperature.

 

[Stu_NY]

Oh, that is good to know Jens- thanks! I have been trying to start it in my unheated basement at about 45 degrees F!