This is my third attempt at an engine.  I have switched to a 4-cycle design, and have switched from propane to gasoline.  It still does not work, and I need your help.
Try moving your intake to the other side of the cylinder so the process goes : intake - > cylinder/ingition - > exhaust. Try a manually adjustable valve for the exhaust. Your exhaust could be releasing too much pressure, keeping the cylinder from experiencing the force. You could also try pressurizing your fuel+air which could give you better concentrations of fuel+air and would assist in moving it into the intake. Be careful with this though.
Good ideas. I think you are right about moving the intake. I actually built a pressurized bubble carb, The first time I tried it, it caught on fire. If you look closely at the board, there is a dark spot behind the valves, from the smoke. You can see that build at howtolou.com/engine, but I got too scared to use it any more. I tallied all 117 suggestions, so far, from hackaday, video comments, instructable comments, and emails. Here is what they said and my responses. <br> <br>15% Check valves are too slow to close. Evidenced by the gasoline splashing back and fire coming out of the intake manifold. Try cam controlled valves &ndash;Lou: I plan to replace the exhaust valves with one cam-controlled gate valve. <br> <br>15% The flywheel should be more massive. Maybe try a wheel and tire &ndash;Lou: I am probably being stubborn, but I have seen a good fire send the flywheel around through all the cycles. I think it will be fine. I plan to focus on getting fire every time, and then look at the flywheel. <br> <br>15% The compression is too low. The valves should be moved closer to the cylinder to decrease space and increase compression. &ndash;Lou: I wrapped foil around the piston and got a nice increase in compression. I also plan to move the valves closer to the head, as suggested, to increase the compression ratio. <br> <br>13% The spark timing is off. Get rid of the string and micro-switch set up. You need something a lot more stable. Try timing gun. &ndash;Lou: See next comment. I think the grill igniter is the main problem. If not, I will switch to a cam driven spark. <br> <br>12% Grill igniters do not have reliable timing. When you push the button there&rsquo;s a short, unpredictable delay until the first spark. &ndash;Lou: I totally agree. I just went out and bought a coil, points, and condenser, at an AUTO PARTS store, but don&rsquo;t tell anyone. <br> <br>12% You aren&rsquo;t getting the right air/fuel ratio Your fuel isn&rsquo;t atomizing properly with the bubble system, so there is an inconsistent fuel/air mixture with each cycle. &ndash;Lou: I was totally ready to give up on my bubble carb, but then someone posted this: http://www.youtube.com/watch?v=xWBWhRZiZ9E <br> <br>5% This looks dangerous. &ndash;Lou: We are not having fun until someone gets hurt  I will wear goggles, at least. <br> <br>3% The stroke is way too long for the air to properly compress and combust. &ndash;Lou: Maybe. I will work on other stuff first and then look at this. <br> <br>3% The spark may be too weak. &ndash;Lou: See comment above about replacing grill igniter. <br> <br>2% Build a better starter motor. &ndash;Lou: Maybe. I hope I don&rsquo;t have to. <br> <br>1% a choke cuts the amount of air through the carburetor to enrich the mixture &mdash; your &lsquo;choke&rsquo; just lets more air into the cylinder and less fuel, thus leaning it out. &ndash;Lou: my &ldquo;choke&rdquo; allows me to change the fuel/air mixture. I think that is all I need. <br> <br>1% This can&rsquo;t be done without precisely machined parts. &ndash;Lou: You are right, so far. <br> <br>1% Hundred if not thousands of engines are operation with intake valve what is essentially a check valve &amp; the valve timing with that is automatic. &ndash;Lou: I plan to stick with a check valve on the intake side, for now, at least. <br> <br>1% Just buy an engine at the hardware store! &ndash;Lou: I wish had thought of that, a year ago, when I started this project!!
your timing is out <br>
Anyway, you had done a great job.

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