[scaleguy]

OK I have an older OS 1.08, (needle valve in standard position, not at backplate), that is giving me major headaches.

I had this engine for a season in a CG Extra 300 and it ran virtually flawlessly the whole time. Last year it was involved in a crash, not due to engine, but didn't really impact to hard as the aircraft cart wheeld on grass.

Cleaned her up but didn't run her again for almost a year. Installed it in my Yak and it has been giving me problems ever since.

First problem is I can't remember what size prop I was running on it in the Extra. I think it was a 15 x6 but not sure.

I had installed a 16 x 6 on it for my Yak to give more prop area outside that big round cowl. The OS manual says up to a 17 x 6 is fine so I thought this was OK.

Had problems starting it and getting it to idle properly so I tried to adjust the low end. First of all what a setup on the low end. They actually call it a mixture control and it is supposed to be for adjusting idle and mid range transitions but is a complicated nut and concentric screw arrangement. I thought I had the idle and transition setup pretty good but every time I opened the throttle past about 3/4 way the engine would just stop. No sputtering just stop dead.

In talking to some people they thought I had over-proped the engine saying that a 16 x 6 was way to big. I tried a 15 x 6 and seemed to get the engine running semi-reliably but the airplane has no vertical with this prop.

They all suggested a 14" prop would do better so I borrowed a 14 x 8 and put it on. Managed to get the engine runing but still vertical is marginal and she really comes in hot on landing even with idle pulled all the way back.

This setup was running good when Flextoposition took her up for a trim flight, (thanx again! ) so I packed everything up and headed to our home field where about thirty minutes later I fired her up and went for a flight. About a third of the way through the engine just stopped dead again, no pre-warning just stopped.

I next tried the 15 x 6 prop. Same problem about 1/2 way through running about 80% full throttle the thing just quit.

On a suggestion I pulled the cowl off to check for bubbles in the fuel line. There were a few at idle speed due to foaming in the tank but as I watched them enter the carb the engine just kept on purring. Even at full throttle a few small bubbles were observed but no sagging in power.

So I richened the engine a bit, (3 clicks), took a flight with the cowl off and proceeded to fly nearly 15 minutes with no problem, brought the plane in for a landing and still purred all the way back to just outside the pitt area where I shut it down.

A couple of things to note here:

With the 16 x6 I was getting about 8100 - 8300 rpms.

With the 15 x 6 I was getting about the same.

With the 14 x 8 I was getting around 7900 to 8150.

I am running 10% nitro with synthetic oil.

The plug has been changed twice through all this and is currently an OS A5 as recommended by the manual.

HELP!

I need this engine to be reliable once again. All these problems allowed me to only fly one round out of 4 at the Stoney Creek IMAC this past weekend and I gota get this sorted out now so I can practice for the next one.

Any help would be appreciated.

Thanx in advance for your input.

[volksman]

you may have answered your own question took cowl off

[scaleguy]

Originally Posted by volksman

you may have answered your own question took cowl off

So then you are thinking a cooling issue?

[ronm]

Jim:
You shouldn't be getting any bubbles in the fuel-line.
Remove your fuel tank and lines, and pressure-check to make sure everything is sealed.
It ran good on the previous plane, so the only thing you could have changed, other than the needle setting and prop, is the fuel system.

What muffler are you using?
Is it the same as on the previous plane?

I doubt it is a cooling issue with that huge open-front cowl.

[volksman]

cooling could be lots of opening on cowl front but can the air get out


fuel tubing on the needle valve fixes a lot of things
or not enough back pressure in the muffler

[scaleguy]

Originally Posted by volksman

cooling could be lots of opening on cowl front but can the air get out

My thoughts after the flight with the cowl off

Originally Posted by volksman

fuel tubing on the needle valve fixes a lot of things
or not enough back pressure in the muffler

Please explain both.

[airframe]

The formula for cooling is you need 3 times the entrance area for air exit.

Mike

[volksman]

cut a small peice of fuel tubing bout an eighth of an inch slip it over your needle right to the tstart of the threaded part an put the needle back in it willact sort like an o ring. try restricting the exhaust outlet if you have changed to another style of muffler . also was it 30 degrees out. the fuel tank should be tight as well

[voyager_663rd]

for what its worth, running the #8 plug in my 1.08 with no problems.

Second, were you having this problem last week when we had the 90o humid weather?

I had the same problems (diff engine although). Overheated just sitting on the ground.

Two deadsticks when it pooped out in the air after less than a minute flying time.

Had to richen it up a lot (at least 1 full turn). Took the cowel off. Ran not so bad.

Does seem likely it might be too hot for it. Any way to add some "exit" holes in the underside of the cowl? Maybe build a baffle inside the cowl to direct air? That wasn't an issue for you b4 but it sure was hot/humid last week if that was when you had the problems.

[AJCoholic]

Just becuase a cowl has a lot of volume, and a large opening in the front, you NEED, absolutley NEED to get the cooling air to pass over the engine's cylinder and case. Otherwise the air will just take the easy way around the engine and not cool it down aedequately. You (as was previously stated) also need 2 to 3 times the exist area as entry to properly allow the air to enter in the cowl and exit out the proper exits. I would make some baffles from 1/8 light ply and glue them into the cowl, blocking airfrow from anywhere but going through the engines' cooling fins where its needed.

Remeber its a glow engine, which is much less tolerant of overheating than a gasser. Baffle the cowl and increase the exhaust area and see what happens.