Hi Geoff,
Is your flame eater to your own design? The port sounds a bit large to me if I'm honest, would it be simple to make it smaller? There are so many parameters that affect when the valve should open! Myself and a member of our club were discussing it a few weeks back at an exhibition. We were surprised to find that mine opened well before TDC on poppin - at least 45 degrees.
However, when the engine is actually running, because of the valve design on poppin, you can get a kind of latching effect, where the 'vacuum' or sub-atmospheric pressure in the cylinder will keep the thin valve against the port face until the pressures equalise and it is ready to open.
If your cam is such that the valve is forcibly opened at a set point, if you open it too late, the pressure in the cylinder will start to rise above atmospheric and you will be trying to compress the gas, sapping power. It's a trade off with the how long the power stroke is, I would try around 45 deg before top dead centre as a starting point.
Another guy on here called madjackghengis did quite a few successful flame eaters and a lot of experimentation. We worked out that one of the good design points of 'poppin' was the whole valve mechanism ... low friction pivots, low spring tension required and a very thin valve that lent itself to sealing well. Also, the cam forcibly shut the valve at a pre-determined point, however, it didn't forcibly open it again, that was essentially left to its own devices providing the spring pressure wasn't too great. This meant it wasn't that critical and relatively easy to get a running engine ... both of my poppin engines ran with the first flick of the flywheel which was a revelation considering the Jan Ridders one I made!
The cam dwell is 110 degrees on poppin but as I said it's very insensitive to cam timing ... I set both by eye and both ran that well I didn't bother messing around with it!
Hope this is of some use and you can get it running ... they are fantastic to watch, don't give up, I nearly did on my first one but glad I persevered. Incidentally, that still doesn't run too well, takes a long time to warm up and is very tempremental. I am planning to one day make a graphite piston and valve for it.
Best regards,
Nick