Hi Ramon
Thank you very much for checking in and giving advice to a novice
and your kind words from an expert are appreciated too
I new you where right - I couldn't find the prop I really wanted to try it with, so I took the next best (or not). One reason for using a big prop came from an advice from Ron Chernich - I have a nice old FOK 15 sport diesel and I had no luck running it with the 7/5" (if memory ...).
Every time I tried to start it, I got a heavy hit on my finger when it fired - it's so fast that the normal smart flick isn't fast enough to get your finger out of harms way. Next step was to try starting it with a stick - that just smashed the prop, since it is more solid than my finger
(there really ought to be a scared emoticon too) - with parts of the prop flying fast all over the shop
- This is why Ron advised me to learn to handle the FOK with a much bigger prop and a 9/6" work wonder on that engine. This was actually the prop I was looking for to test the Viking.
Your comment made me go down to the workshop and look for all my props (not that many) and in the box with engines I found a 1HP 7.5 cc glow with the same size prop that I had on the Viking - OK, that is really in the very heavy over prop territory
Soon after I found the FOK and the 9/6" was still on it - took it and drilled it up to 9.5 mm so I could mount it on the Viking and tried to start it again. A little harder to start than with the bigger prop - smaller flywheel effect being 2" smaller in diameter - it ran quicker, but not enough. Found a 8/4" and tried that too - much better, but still no joy in regards to get it up to flying speed.
I'm sure the 8/4" is the right prop (or very close), but it still can't "clear it's throat". It runs fast enough to easily see that there is a big spray back out the carb - bigger than what can be seen leaving the exhaust. This kind of confirms that size not always scales down well and that I really need to get my hand on some cast iron for a new piston, so I can make a new much closer to the original inlet timing. I do also think that I might need to make a new carb or find a way to cure the original of any leaks - though that will only happen if a new piston can't cure the problem.