Dutch,

It's just an engine, so unless the design is known to have mechanical failure, I would work though the issues.

First of all you having a fuel/air problem. Either to much air (leaking) or to little fuel (obstruction).

Here is how I test for leaks. I hook up the exhaust nipple and needle valve to the fuel tank just like how you are going to run it. Then I open the carb, blow in the exhaust, then rotate the prop until the air is escaping though the carb. This means that piston is all the way down exposing both the intake and exhaust ports. With the piston down and air coming though the carb I now put my finger over the carb. What this is doing is putting pressure in the crankcase, tank, and all of your hoses. You might feel a little air leaking out though the front bearing but that is ok as long as it is very little. If your setup doesn't hold pressure figure out where the air is leaking from and fix it. A tiny little leak at the carb or needle o-ring will cause all sorts of strange problems.

To test for obstruction I typically hook up a tube to the needle valve, open the carb, and try to blow though the whole thing. If there is an obstruction you can detect it, but it's hard to describe. Perhaps the easiest way to get a feel for how little is too little is to try it on a known good engine. If the ST feels like it builds more pressure then there is something in the way. A couple of things it can be is the hole in the carb intake barb isn't lined up with the brass insert ([link=http://www.rcuniverse.com/forum/m_2290854/mpage_4/key_/tm.htm]read post 95 for more info[/link]) or it could be some junk in the carb/needle/tubing.

While I agree that the quality control of some cheaper engines isn't that great causing problems like this, they are almost always resolvable with a little work and understanding.

I run a magnum 70 4 stroke on my twist and while it did take some tuning and playing with different fuels/plugs to get it working right, it now turns a 14x4w at 9800 rpm which hauls the twist around quite well. Best of all, I only paid $125 for the engine.

Always remember the 7 P's: Piss Poor Preparation Promotes Piss Poor Performance.

schu