Engine is an ASP 46. Got it used from a guy who claimed it didn't have much mileage on it.

Idle on the engine was set very rich, so I leaned that out considerably. After tuning, the pinch test on idle as well as full throttle results in RPM's speeding up, so all good. Temps measured with infrared thermometer comes in at about 70-80 (160 - 175 deg F) degrees Celcius on idle and up to a max of about 105 degrees (221 deg F) on full throttle. Exhaust is dumping a lot of oil, so must be rich enough. I am using "80/20 castor straight". Glow plug is medium heat and brand new.

After about 5 mins of mostly idling, the RPM's drop a little and I can hear the engine struggling. If I then throttle up too fast the engine just dies. This happens consistently after 5 minutes, every time. Compression is good when the engine is cool, but when the engine dies, it is way reduced. Motor does not start again until 5-10 minutes later when it has cooled down. I tried dumping some fuel on the carb and inlet to cool it down, but this doesn't seem to work.

Any idea what is wrong? Thanks in advance!<br type="_moz" />

Has it been run on straight castor its whole life? It might be varnished.

Unfortunately, I don't know. What is varnished?

Five minutes of idle is a pretty long time. The engine will "load up" with fuel if it is allowed to idle very long. Then, when you open the carb very fast, it floods the engine and causes the glow plug to die. It sounds like you have a very good running and well tuned engine. After an extended idle, you will just have to slowly increase RPM's to keep from flooding the plug. Regarding the compression, the drop in compression is normal when the engine is hot because the cylinder has expanded more than the piston. In a lot of the newer ABC or ABN engines (no compression ring), they sometimes have no compression when hot. That's also why they won't start until cool. No compreesion to draw fuel into the engine head. I don't think you've got anything to worry about. I would suggest using less caster in your fuel. Either a blend of castor/synthetic or all synthetic. All castor in this type of engine will lead to varnish issues (i.e. a very gummed up engine).

Thanks for the replies guys! I will try to run her at half throttle for 5 minutes and see if she keeps going. Good to hear that lack of compression when hot is normal, no need to toss the engine just yet

I was going to say the same. Five minutes of 2-stroke idle is pretty long. I usually bump the throttle a little after 20 or 30 seconds or so just to keep the carb clear. You may not have a problem. Fly it and see.
Edwin

be careful running the engine on the ground. I would take the cowling off if it is and keep a close eye on engine temps. I think your engine is loading up from idling too long. I think the best test for mixture setting is pointing the nose up. Good luck

Man, put that joker in the air and fly it!

No kidding, if it will pass the pinch test and idle for 5 minutes before heating and loading up just fly it.

Hi, I have a pair of OS FX .25 I am breaking in to fly in my TwinStar. One engine is ready, but the other has developed a problem I have not come across before. While adjusting for optimum rpm, it allowed me to completely close the needle valve without stopping. The engine ran perfectly, and did not get hot. It behaved as though the engine was set for optimum running. The suggested needle setting is 1 1/2 turn out. I would appreciate any help or suggestions. I have found nothing wrong anter checking and re-checking. Many Thanks for your opinions. Rich