I have an OS .75. I flew it around 20 flights and couple of crashes. The first two flights are ok, no problem doing loops, rolls or hammerheads. In the third flight after a hammerhead the engine kills. This is the second time this happens!!!. I've been lucky to land it without mayor problems, but I am puzzled about it. Any clues?

Thanks

pbuenafama,

If the crashes were in the dirt you may want to clean the engine up, especially the carb. Pull the high speed needle valve out and clean it as well. Run the engine a little richer and see what happens.

Yea... after three flights, you're out of fuel

Sorry, I couldn't resist.

The first thing I would check is to make sure that you're not running too lean.

In a-lot of situations like yours some very sage and experienced RCU members would have you inspect tour tank and clunk.

Bill

Maybe its overheating from running too lean,too big of prop or running flat out for too long.Also a new glowplug ouldnt hurt.

The most common mistake I see with beginers and OS engines, is trying to run to big a prop and make engine have high pitch whine. All your doing is leaning out engine to a point it's not going to fly. Most all of my engines are OS and I have learned the literature they give you about prop size that you can run is not true. I have OS 75 on 10# Spade Plane my son built, 12x8 prop 11,000 RPM. This combination flies well.

I agree with checking the clunk. A hammerhead runs you vertical long enough to run you dry if the clunk is stuck in the front of the tank. It may still run OK in all other attitudes. I would start with checking your tank.

Duh !! Forget the third flight. Just go directly to the fourth flight. Problem solved !!! OK, just had to say that, sorry. Does the motor have time to cool down between flights? I'm not that familiar w/ OS engines, but I'd check the head gasket or if it don't have one, check for any small cracks or warpage.

I have cleaned the carb after my crashes and that was long time ago. I let the engine rest for 20 - 30 min after a 13 min flight. I have a big tank to fly up to 15 min, and I think the clunck is working ok since in the first two flights I do all kind of acrobatics, specially hammerhead. I don't think I have leaking since the firewall is always dry after each flight. I have a 13x6 prop, and I set the high speed neddle at the top of high pitch whine. If running too lean is the problem, why the first two flights are ok? My engine is mounted at around 270 degrees, would that be a problem? Attached is a engine size vs prop size. I think I am within the range....

Thanks

pbuenafama, you are going to have to physically check clunk and tank for leaks, once satisfied everything is ok, tune engine like you normally do, then richen engine 2 clicks. You should be able to tell pretty fast if engine is going to stay running. If not land and richen 2 more clicks or untill engine stays running. If you don't have a tach, get one and this will help you determine how your engine is running. Top of high pitch whine is not always best tuning point.

Either the clunk is out of the fuel or it is too lean, my vote is too lean. You are not gaining anything by tuning to the highest pitch and max rpm, rich up the needle a click or two or three! Remember the fuel is also the lubrication, I will bet that engine is very hot when it dies.

Yes, if you physically find no problem with the clunk, then look for some other cause for it to go lean. When you tune your engine, have a helper hold it vertical. Tune it for a solid high RPM in that position. This will insure you don't have it too lean. Also check your pressure line for leaks or holes.

pbuenafama, have you had any luck getting your engine running?

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