sledge_78

My Feedback: (24)

I have a Webra .61 Blackhead that appears to fade out on power during flight. I'm using 15% nitro fuel 18% total lubricant (1/2 caster & 1/2 synthetic. On this fuel the engine seemed to run hotter than normal. I switched to a 5% nitro & 20% lubricant. This seemed to run the engine cooler but there was less power and it still faded after a few minutes of flite. The engine basically slowed down and full throttle would not make any difference. I have a brand new tnII carburetor which I cleaned out to see if it would help. I dissasembled the engine and made sure the exhaust pressure nipple was clear just to convince myself that I was maintainiing pressure.

The problem persists, I could use help solving this one . So any of you Webra or engine experts, please advise.

Gerry

w8ye

My Feedback: (16)

Not being there it is hard to say.

But I'll put my bets on the fact that the engine is still getting hot. Is the engine in the open?

Vibration could be present and the fuel is foaming causing the engine to go lean after a short time?

Ernie Misner

By chance is the carb higher than the tank centerline? Think the tank is holding pressure well; did you test it before instalation? I would look for possible air leaks in the engine also that could contribute to a lean condition. Webra's (European) aren't usually set up for much nitro. You might try adding a head shim and then going back to the 15% for power. What are you running for an exhaust system? Too much backpressure (as in too small stinger size on a pipe, long exhaust deflector, etc.) will make them run hot and will make the needle valve feel like it's difficult to get rich enough.

Just some thoughts,

Ernie

Turk1

Did you try to adjust high end needle valve while your plane s nose full up?Try to do this then fly.I hope you can have some improvement.

NM2K

My Feedback: (14)

-------------


Webra Blackhead sixties were set up to run on FAI fuel (0% nitro). The problem you are seeing is too much nitro for the compression ratio. Either reduce the nitro or reduce the compression by adding a headshim. Also, those engines were designed to swing 11" props. Much more than that and you will encounter the same problem, even with reduced nitro and compression.

You have a stellar performing engine for the era. Don't fry it by operating it overcompressed or with too much nitro or prop, please.

sledge_78

My Feedback: (24)

Artisan,

I tried a 5% nitro 20% lubricant as mentioned. It appeared the engine was much lower on power but still had the fade. Though it did appeared to run cooler. At first, I used an 11:7 prop. All seemed great then on the 15% nitro fuel, it just seemed to run hot. I changed to a 12:6 prop and I can't seem to remember if the problem started then or slightly afterwards. The change in props was made to slow the airplane down more for landing. (The airplane is a HOBBISTAR 60) I will try returning to the 11:7 to see if this helps. I appreciate your comments, and all of the help I've been receiving from the responses.

I have also read here, that an vacuum loss at the front bearing may cause this problem. since it is an older engine , maybe this could be a factor. When this Blackhead ran well it was extremely powerful and responsive to the throttle. Now I'm forced to land after a few minutes because the power reduces, and I feel the engine will quit first before I can land.

Gerry

Chrispeace

I have a Webra Speed 40 of 80s vintage (a beast of an engine even by today's standards) that had worked fine until I tried running it inside a cowl with insufficient cooling flow. It suffered exactly the same syptoms as you describe and smelt hot after landing. To solve the problem I baffled the cowl to direct all the inlet air across the cylinder head and closed off a cheek outlet that allowed the cooling air to exit the cowl rather than flow past the engine head (ratio should be 3 units out :1 unit in and it must flow past the head to be effective). This transformed the set up which now works on even the hottest of UK days (yesterday 32 Deg C). I run mine on 0% and castor (called 'Straight' here in the UK) and get more than enough grunt as others have said Webra's don't require Nitro. On the prop issue I have just up'd mine from a 10x6 to an 11x4 to improve 3D pulling power. The Webra just eats up the extra disc and shows no signs of overheating.

Hope this helps to shed light on your problem.

jaka

Hi!
You can use a 12x6 or 13x5 if you want..these props will give you better performance than a 11x7 if you use the engine in a trainer aircraft or sport model .
You should also run 0-5%Nitro and use a Enya 3 or OS 8 glowplug.
Tank size should be 12-14oz.

It seems to me that you run your engine to lean! Have you hold the airplane straight up when you set the high speed needle...you should always do that! Hold it still straight up! Do not shake it!
If the engine can hold its setting in that position it is very likely that it will maintain rpm throughout the whole flight. But remember to always set the engine a little rich! That's Very important.

Regards!
Jan K