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-----Original Message-----
From: Ed Burkhead [mailto:[EMAIL PROTECTED]
Sent: Tuesday, April 05, 2005 11:49 PM
To: [EMAIL PROTECTED]; Coupe-List
Subject: RE: [COUPERS-FLYIN] carb help----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----
Lloyd asked:
> I have a question for you, why does my engine run better on
> the ground when the carb heat is applied ?? I also have the
> Stromberg. Yes, I am an A&P ....But have . no experience
> with these carbs. Help.
Lloyd,
I’m not a mechanic and I shouldn’t play one on the Internet. I got hives answering that previous question and hope I didn’t step on it.
Here are thoughts about your situation:
If it’s running rough on the ground when set to full rich but improves when you pull carb heat – maybe you’re running too lean on the ground. Carb heat thins the air as it heats it so it richens the mixture.
As you climb, the mixture gets richer and richer. If you’re too lean on the ground, you may be just right higher up so it may run just fine in cruise. I think the Stromberg richens the mixture at full throttle, like many other aircraft carbs, so that may be why you’re not getting detonation during full-power climb.
Then it follows that if you’re too lean on the ground, you need some maintenance.
Since you haven’t messed with Stromberg carbs, you probably don’t know that they have air passages inside. As I understand it, the air pressure through these passages governs the air pressure in the float chamber of the carb.
Controlling the air pressure in the float chamber controls the mixture.
My relevant experience:
I once had a fiber-type air filter on my Coupe. During an owner-assisted annual with a mechanic I wasn’t used to (at my college town), he or I cleaned the air filter.
On the next flight, I decided to go for a social call to my old A&P/AI about 130 miles away – just to have somewhere to fly. As is my custom when it’s thermally and bumpy, I went high to 10,500 or 12,500 for the smooth, cool, summer air.
Just before my destination, I did a cruise descent at lowered power. When I got down to near pattern altitude, about seven miles from my destination, the engine was running rough. It was still developing good power, though.
My instant, first reaction to a rough engine is to pull carb heat while the engine is still putting out enough heat to melt any carb ice. The roughness instantly decreased – but not all the way.
Now from my reading, I didn’t think that’s the way ice should react to carb heat. I think (still theoretical to me) that the engine might get even rougher for a moment or two as the ice melts, then get normal. But this got better instantly.
So, I think to myself, richening the mixture helps. (My mixture was wired full rich since before I bought the plane.) The only other thing I can do is test full power to see if that richens things up to normal. At full power, it ran smoother.
By this time, I was only about 2-3 miles from the airport so I continued to a nice landing.
My pretty-experienced A&P/AI popped the carb off the engine and took it to his bench. He found that those air passages, or at least one of them, was clogged with fibers that looked just like the air filter fibers. He cleaned out all the air passages. (Randy Tarlton at Perry, Iowa)
Since he had the mixture assembly apart, he naturally cleaned it, too. I can’t remember for sure, now that I think about it, but I think we hooked up the mixture control knob and I tested leaning on the way home.
Back to speculation mode:
As a NOT an expert, I’d suspect that your carb needs attention from someone who understands them or from yourself with coaching from some of our list experts.
As I understand it, the mixture control has a moving plate with holes in it and a stationary plate with one hole (or visa versa) or something (my memory of this is 23 years old – sorry). The moving plate changes the match-up to varying size holes to change the mixture by changing air flow. I’ve read that sometimes, when reconnecting the mixture on a Stromburg, it’s necessary to lap the two plates together with lapping compound. Then clean and reassemble.
This info may help. At least it’ll spark any dissenting and more detailed how-to answers from the real experts. Please let us know through the list what you find out.
Ed Burkhead
http://edburkhead.com
ed -at- edburkheadQQQ.com (change -at- and remove the QQQ)
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