Slobbering Rich to Full Bore

What would cause an engine to be running so rich on the ground it barely makes it into the air but once it gets airborne it almost immediately goes to full bore. The engine in question is an old Enya 29 on a profile. Have tried a Smith uniflow and a GRW Chickenhopper with the same performance from both. Thanks

This is a good question. Basically your plane is unloading in the air. Ther're several reasons this could be happening. The areas to check could be props. Is it loading the engine too much on the ground? Glow plugs, fuel and tank placement can also be problems. Are you using muffler pressure or not? sometimes it helps to do that. Yoou could also be needing to look at your venturii opening size.

I'm sure that others more knowlegable than I will soon give you more help.

John

Check for excessive vibration. You might want to isolate the tank more thoroughly. Also, you may need a "tripler" on the IB side of the nose.

Sounds like you are getting very little fuel draw. Check the position of the spray bar jet in the venturi. Or start the engine and set it slightly rich, then point the nose up and note how lean it gets. If it goes too lean or quits, you have a fuel draw problem.

I was out flying Sunday and I had the same problem. Rich on takeoff..leans out in the air. I switched from a B-Y&O 12-6 to a B-Y&O 12-5 and now when the engine is set on the ground, there is little difference in the air. BTW I'm using Fred Kreuger's chicken hopper profile 4 1/2 oz tank too. Works real well. I'm using a SSW OS 35FP .
Crist

Glad you got your problem sorted out! I haven't got back to messing with mine yet. I do think I'll try out a clunk tank so I can just put enough fuel in it to test things out and not be committed to 8 or 9 minutes of an engine cooking lean run if things go awry. I had one flight where it was so rich on the ground the plane had trouble moving through closely cropped grass. It would move a few inches then stop for a bit, move a foot more then stop again, Finally got enough speed after about 30 seconds to drag the plane into the air. Went lean almost as soon as it got in the air, probably within 1/4 of a lap. At least on that flight it started out rich enough it didn't go horribly lean in the air.

The standard uniflow tank and especially the GRW chickenhopper protrude a long ways out from the fuselage. The engine has to draw fuel a long ways uphill against the rotational force. Prior to launch, this effect is not present, thus the engine must be set on the ground to compensate in the air.

I believe Brodaks sells a version of the old Veco profile tank (originally designed by George Aldrich). This tank does not stick out very far and brings the pickup close to the venturi. As an alternative I can send you drawings of a home-made chickenhopper tank that has the fuel pickup close to the venturi.

You can test the 'uphill' fuel draw theory by using a small tank (1 oz or so) that does not stick out very far. It will only give you a minute or so of flight, but it will prove out the idea before you invest time or money in a different tank.

Do you have the Enya 29 with the square intake? If so, it will need a restrictor to run on draw. What happens if, on the ground, you hold the airplane with the outside wing pointing straight down? Fred is right that any engine has to be set on the ground for how it will run in the air, but I don't think this is any more of a problem with a uniflow or chicken hopper on a profile.

The Enya is one with the round venturi. Currently using a 10-5 APC. Vibration doesn't seem excessive. Less than a Fox 35. Will try extra padding on the tank and try some other tanks plus check some of the other things mentioned to see what happens. Thanks Much

>The Enya is one with the round venturi.
>Currently using a 10-5 APC. Vibration
>doesn't seem excessive. Less than a Fox
>35. Will try extra padding on the tank
>and try some other tanks plus check some
>some of the other things >mentioned to
>see what happens. Thanks Much

OK, that was July 13th. And it was an unusual symptom. The only Enya 29 I ever played with had the square intake and shiny black venturi inserts of two or three sizes, plus two kinds of heads. It acted nothing like yours. Ran pretty much the same as any of the engines of its type do (no stunt break, just variations from a rich two stroke through a leaner one, and nowhere near as much unloading after launch - with 9-6's). It seemed a little chunky and heavy for its displacement and power output, and was traded away.

What was the outcome of any further experiments with tanks and props?

Haven't messed with it any since then. I've got another Enya of the same type and might just put it on the plane when I decide to take it out again and mess with the problem engine again in the Spring.

>Haven't messed with it any since then. I've
>got another Enya of the same type and might
>might just put it on the plane when I decide
>to take it out again and mess with the problem
>engine again in the Spring.
>
Well, Rats! I thought we'd have some revelation of finding something on the plane and thinking you'd told us about it.

Now we hafta wait three or four months? (Sigh!)

K.