John,

 

That sounds like what I had happen once on my Coupe.  Symptoms:  After flying high with the engine running smoothly, the engine ran rough after descending.  It was almost smooth at full power.  I only had 6-8 miles to go to the airport so I continued and landed on the airport.

 

 

After you check the easy things like the linkages and whatever else others here recommend, you might want to do the following.

 

Caveat:  This only applies if you have a Stromburg carburetor.

 

The Stromburg carb does mixture control by using a plate with multiple holes that slides against another plate with, I think, a single hole.  The multiple holes were drilled so that, as you pull the mixture, the successively larger holes match up with the fixed hole allowing more airflow through the hole.

 

Under the fixed hole is a tube that goes, I think, to the venturi of the carb and this mechanism varies the air pressure in the float chamber and this controls the mixture.

 

In my plane, the tube through the carb was clogged with fibers from the recently cleaned fiber type of air filter (which I never used after that day).

 

We cleaned the tube through the carb, cleaned the moving and fixed plate, cleaned the chamber in which the plates sit and reconnected the mixture.  The mixture worked fine the remaining time I owned the plane.  I seem to recall a recommendation that the two plates with holes be lapped together so they fit together very well – I’m not just sure about this – perhaps rub them together with lapping compound between them.

 

Altogether, removing the carb, disassembling it, cleaning, reassembling and remounting it took about an hour and a half if I recall correctly.

 

It was really worth it.  I used the mixture control to good effect in many cross-country trips.  You can see further discussion on mixture in the paragraphs I wrote for the FAQ at http://www.ercoupe.org

 

Ed Burkhead

http://edburkhead.com/

[EMAIL PROTECTED] 

 

-----Original Message-----
From: John Bennett [mailto:[EMAIL PROTECTED]
Sent: Saturday, July 19, 2003 4:53 PM
To: [email protected]
Subject: [SPAM] [COUPERS-TECH] Running rough

 

Hello Coupers,

I've had 2454H for about four months.  I went flying this morning.  The purpose was to calculate fuel burn. After topping off the tanks, I took off and climbed to 5500' and returned to the airport.  I was at full throttle until descent to land. Total time from engine start to stop was 00:43.

    After topping off again with 3.15 gal of fuel, I took off and climbed to 4000'.  When I reached altitude, I was at full power, indicating 122 MPH on the GPS.  My plan was to fly out for 00:30 and return.  I tried to lean the mixture but with the mixture pulled all the way out I only saw about one or two hundred rpm drop so I returned it to full rich.  I wanted to descend to 3000' going back so I pulled the throttle back to 2100 rpm. It started running rough.  I went back to full throttle and it smoothed out after a few min.  By this time I'm heading back home.  After flying about ten min. I pulled the throttle back again and again it started running rough and losing rpm.  I went back to full throttle again and it smoothed out for the most part.  I will say that even at full power, it still seems to run a little less smooth than it did.  At one point the rpm’s went down to about 1500.  It was starting to get scary but it smoothed out again and I kept my speed and altitude until I was within gliding distance of the airport.    By the time I reached the airport it seemed to be running normally. 

I am flying a D model with, I believe, all the E up grades. C-85 engine, rudder peddles and split elevator.

Can anyone offer an idea of what to look for? 

Thanks,

John Bennett

N2454H

 

 

 

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