tangerine-jack

I've been looking at the past posts and I haven't found a direct answer to my current problem.

I have a Cox medallion .09 R/C, it's been running great, so I decided (probably against better judgement) to tap the crankcase pressure to the fuel tank. I understand that at idle it will have a tendency to flood, I'm OK with that as I normaly run WOT until it's time to hit the tree, uh I mean land. However, it runs great at WOT for about 2 or 3 minutes, then it dies out.

Any ideas? Do I need a bypass valve of some type, one way valve on the pressure line, or a pressure regulator on the fuel line? I'm using a Sullivan 2 oz tank with two lines. Should I re-plug the crank tap and forget about it all together and use atmospheric venting like I've been using? I do like the idea of some pressure in the tank for steady fuel feed, but if it's more trouble than it's worth, then I can live with that also.

Could it be fuel foaming because I changed from a 1oz to a 2oz tank?

Thanks!

brED

Hi Tangerine,
to tell you the truth I've never tried to tap a crankcase, but I read in another forum some time ago that said you need a check valve. Problem is, I don't know of any check valves that are small enough to use in 1/2A. In fact (I had to double check this) it's in the post below here titled "lean half way thru the flight". try talking to someone in that discussion, they should be able to help you a little better than I can .
Bread

ClemenTang

if you tap under the carb in the red plastic you shouldn't need a check valve. Does it have a molded spout? The tap is already timed since the cranked shaft opens it when pressurizing and closes during vacuum. You only need a check valve if the tap is always open, e.g. installed at or about the backplate. And for a two line tank it's not only pressurized, it's pumped. It can boost performance if you enlarge the venturi altogether. Problem is it may flood the engine and a regulator is needed.

Clement

tangerine-jack

OK, I am using the tap that is built in to the body. I noticed the 2 oz tank was a tight squeeze, too tight it seems, and I put the 1 oz back in and presto! Seems the problem was fuel foaming because the 2oz tank really didn't fit and the foam was crushed solid. I can now get about 8-10 minutes of WOT with steady, smooth power for the duration of the flight.

I know I should have only made one change at a time, but it's not my style! BTW, the pressure tap makes a noticeable difference in performance, wish I had known about it before!

ClemenTang

If you still want to use the 2oz tank you may try thinner foam or dabs of silicone sealant. Your foam was too thick it's just vibration not large amplitude rattling to deal with.

Clement