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  #11  
Old 06-23-2019, 07:59 PM
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rocketbob rocketbob is offline
 
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Quote:
Originally Posted by 71459 View Post
The carb is a 10-5009. Thing is this is exactly the same carb model that I had before, which worked perfectly for 15 years! It's also the "factory" carburetor for my engine, an O-320-E2G.
10-5217 or 10-3678-32. Works way better than the 10-5009.
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  #12  
Old 06-23-2019, 08:04 PM
71459 71459 is offline
 
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Originally Posted by William View Post
Any chance the plug wires were run to the wrong cylinders, have you checked your mag timing? At the time the issue appeared was any work done just prior?

Bill
I installed a brand-new harness. I carefully re-timed the mags when I did that installation. I checked the harness labels as I went - I believe it is all installed and set up correctly. The engine starts and idles OK - it's just when the throttle is advanced that it "loads up". The mags are still suspect, but I don't know if faulty mags would cause this.
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  #13  
Old 06-23-2019, 08:32 PM
71459 71459 is offline
 
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Originally Posted by rocketbob View Post
10-5217 or 10-3678-32. Works way better than the 10-5009.
Maybe my old one had a different jet - I can't say for sure.

But what's strange is, even with the "wrong" jet, why would the engine keep running at idle cut-off?

It's almost as though the mixture control inside the carb is not right. I'm just guessing at this point.
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  #14  
Old 06-23-2019, 08:42 PM
William William is offline
 
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Was the plug wires installed prior to the issue? When you retimed the mags did you make sure to rotate the prop past the timing degree to get the impulse cupling to snap before setting timing? On the magnetos if the internal points setup changes do to cam ware or the screw loosening weird things can happen as well but not likely for both to go out at the same time. It sounds to me like your timing is way off. You’ve confirmed you got the fuel and the air so the last thing is the spark.
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  #15  
Old 06-23-2019, 08:49 PM
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1001001 1001001 is offline
 
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Quote:
Originally Posted by 71459 View Post
Maybe my old one had a different jet - I can't say for sure.

But what's strange is, even with the "wrong" jet, why would the engine keep running at idle cut-off?

It's almost as though the mixture control inside the carb is not right. I'm just guessing at this point.
I had a similar problem with my Warrior, in which the engine would keep running at idle cut off (quite roughly). The problem there was that the two halves of the carburetor had become loose from each other, and allowed excess air to be drafted in through the gap. How this caused the engine to keep running is unclear, but the increased mass flow of air may have induced more fuel flow than expected at the idle cutoff setting.

If you have replaced the carb with a known good unit, perhaps that is not the problem, but an induction air leak downstream of the carb could possibly be causing a similar problem to what I had. I am not familiar with your engine type but could there be a damaged intake tube or gasket?

Are you seeing any anomalies in manifold pressure when this occurs?
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  #16  
Old 06-23-2019, 09:29 PM
71459 71459 is offline
 
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Quote:
Originally Posted by William View Post
Was the plug wires installed prior to the issue? When you retimed the mags did you make sure to rotate the prop past the timing degree to get the impulse cupling to snap before setting timing? On the magnetos if the internal points setup changes do to cam ware or the screw loosening weird things can happen as well but not likely for both to go out at the same time. It sounds to me like your timing is way off. You’ve confirmed you got the fuel and the air so the last thing is the spark.
Well the mags were both completely off, so I did a "fresh" re-install using the "L" pin hole on the back of the mag, ie, without the harness on and timed them that way. The engine starts right up, but now you have me wondering if the impulse coupling is not disengaging properly. Hmmmm

The problem was the same using the old harness and without touching the timing. I think the timing is good, but I wonder if the mags are damaged internally. On the other hand, what's making the engine continue to run with the mixture at idle cut off? Confusing..
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  #17  
Old 06-23-2019, 09:36 PM
71459 71459 is offline
 
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Location: Seattle, WA
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Quote:
Originally Posted by 1001001 View Post
I had a similar problem with my Warrior, in which the engine would keep running at idle cut off (quite roughly). The problem there was that the two halves of the carburetor had become loose from each other, and allowed excess air to be drafted in through the gap. How this caused the engine to keep running is unclear, but the increased mass flow of air may have induced more fuel flow than expected at the idle cutoff setting.

If you have replaced the carb with a known good unit, perhaps that is not the problem, but an induction air leak downstream of the carb could possibly be causing a similar problem to what I had. I am not familiar with your engine type but could there be a damaged intake tube or gasket?

Are you seeing any anomalies in manifold pressure when this occurs?
That's interesting - so idle cut off is not necessarily 100% complete fuel cut off.

I don't have a manifold pressure gauge in my airplane so I can't say about that.

I have not disassembled and examined the intake manifold. From the outside, it looks perfect - like new.
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  #18  
Old 06-23-2019, 10:36 PM
PCHunt PCHunt is offline
 
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Default Improper assembly?

When a carburetor is assembled, and the bottom half is bolted to the top half, it is easy to make the mistake of not ensuring that the mixture control from the top half gets properly inserted into the mixture receptacle in the bottom half, or the bowl.

Your symptoms sound very similar to problems caused by that improper assembly. The only way to check it is to take the bowl off the carb, and see where the mixture control is located.

The mixture control rod that sticks down is flexible, and it's easy to miss getting the rod into the receptacle.
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  #19  
Old 06-24-2019, 07:18 AM
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snopercod snopercod is offline
 
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Here's a photo of the mixture metering valve (that half-cylindrical thing on the springy shaft, just to the right of the blue float)

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  #20  
Old 06-24-2019, 09:25 AM
71459 71459 is offline
 
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Quote:
Originally Posted by PCHunt View Post
it's easy to miss getting the rod into the receptacle.
I did have the carb apart (several times). Could I have botched assembling it and not gotten the mixture value in its seat? I recall it's pretty much a blind operation, guiding the valve down into place. I'll take it apart and double check it.
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