Flew my plane with an OS .65 LA today and had no problems the first 3 flights. I did the normal engine priming prior to starting for the first flight. After flight #3, I went for a 4th flight and couldn't get the engine started. I didn't prime it as I never have to after the 1st flight of the day. After several failed attempts to start the engine, I primed it and still no start. While I was spinning the prop with an electric starter, the RPM seemed good like it might start, then after a few seconds the RPM's would decrease. I then removed the glow plug, turned the plane upside down, and turned the prop to try to clear the head of fuel. Only a few drops came out. Next, I re-primed, and it still wouldn't start. I removed and replaced the glow plug, tried to start again, the engine started, revved real high, then died. This happened twice. I finally got it started, did a run-up on the ground, it sounded good, got the plane in the air, but the engine was sluggish. It was running rough and with the throttle fully open, it was acting like it was at 1/2 throttle. I landed the plane to try an adjustment, the engine died and wouldn't start. Anyone have any idea of the problem? I might add that the flying took place in AZ, it was a very hot day. Don't know if it was purely a overheat condition.

Hi TPL
Is the engine mounted as a PUSHER, with a pusher prop?

Dirt in the carb? Remove the hs needle and force some fuel through it.
Fuel line cut? Check lines in and outside the tank, check pressure line and port too,

OK, I finally got to tearing the plane apart to find the problem. One more thing to add, the last few times I flew the plane there was a vibration you could hear on the ground and in flight at 1/2 throttle. This sounded like an airframe rattle or maybe some flutter. As I began to remove the engine, I found the following problems:
1). The fire wall which the engine mount is attached to is loose and definitely requires re-gluing. Probably the cause of the vibration noise I'm hearing.
2), On the OS 65 LA, the HS needle is a remote needle, attached by a bracket from the back of the engine and sitting to the right rear side of the engine as you're looking at it from the front. All 3 screws holding this bracket to the back of the engine were loose, the bracket was loose surely causing severe vibration to the needle valve.

So, not being an engine master by any means, is there a good chance my starting/running problems were caused by the vibration of the engine being loosely mounted because of the loose firewall, and, due to the vibration that the HS Needle was getting from the loose engine mount and the HS Needle Bracket being loose? I can imagine that the prop was also changing angles constantly probably not helping matters. I'm also going to check all fuel lines and run fuel through the needle valve in case there's any dirt in there. Thanks for the replies.

If the needle-valve bracket screws were loose.. it stands to reason the back-plate might not be tight.. and letting just a seep of air into the crankcase. That would create just the problems you're describing. The firewall being loose doesn't lend to a smooth running system either...

It just stands to reason in my mind.. and the needle vibes don't help either.. but keep a check on those back-plate/bracket screws.. the problem might lie therein.

Once you get it all tuned up, you'll probably find it to a whole different plane. Good luck.

I have used a lot of the .40 and .46 LA series engines, not the .65 very often but the one thing they all had in common was the screws would come loose. Whenever I had a new one the first thing I did was pulled the screws one at a time and put a dab of locktite on the ends and then tightened them back down, let the engine sit over night so the thread locker was dried. Loose screws allow air leaks then create operating problems, I think Mr. Grant has the right of it with a loose back plate. With a new engine the glow plug can also get fowled and create a problem.