Engine running rough

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Pops

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Yes, the mixture metering valve can be put in backwards. Makes the fuel shut off with the mixture knob in instead of out.
Daughter and her husband bought a cessna 150 that was seating in a hanger and the owner couldn't get it to run except on the primer fuel. Gave up and wanted to sell it. They bought it and I took a carb off another 150 and put it on and flew it home.
 
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Dan Thomas

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Ok. I thought the jet and nozzle is one piece that mounts inside the carb body. So the nozzle and the jet can be separated from each other? Didn’t look like that to me, but I guess you might be right. Well is in the mechanic shop now. I will talk to him on Monday.
They might be making them that way now. I thought you figured the jet was just machined into the carb casting.
 

Dan Thomas

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I think you have more than one problem or something else got damaged working on the carb. It’s been too long since I have taken one apart. Can the mixture metering valve be put in backwards? I would think about if the fuel
can draw through accelerator pump somehow. Something not seated. No backfires lately? Mags are timed right?
The mixture control can't be assembled backwards. The female part of it screws into the carb body, and if it comes loose it leans out the mixture and can cut it right off.

And yes, I once had a new engine running rough because the accelerator pump was letting fuel though it during high power ops. One of the tiny check valve springs in the pump assembly was missing. It needs to be there to prevent fuel delivery unless the throttle is opening. But it's a high-power thing, not low power. It only happens when the airflow through the venturi is high.
 

Dan Thomas

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Yes, the mixture metering valve can be put in backwards. Makes the fuel shut off with the mixture knob in instead of out.
Daughter and her husband bought a cessna 150 that was seating in a hanger and the owner couldn't get it to run except on the primer fuel. Gave up and wanted to sell it. They bought it and I took a carb off another 150 and put it on and flew it home.
It must have had the lever installed 180° out? There's one flat on the shaft to prevent that.
 

Magisterol

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They might be making them that way now. I thought you figured the jet was just machined into the carb casting.
Never saw the jet/nozzle thing. i only saw the manual and that was my conclusion albeit wrong apparently.
 

Pops

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It must have had the lever installed 180° out? There's one flat on the shaft to prevent that.
Sent the carb out to be overhauled and they said the metering valve was backwards, maybe they meant the lever ??
Got the overhauled carb back and replaced the loaner carb and all was good.
 

Talon38

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I have the bulletin. There is no rpm rise on shutdown. The idles mixture might be too lean. Other than that, the engine I keep it lean from take off to landing, because otherwise the roughness is getting to bad. Funny thing is that on the ground the vibration from the roughness is not that bad. This is another thing that I don’t understand. Why the roughness is worst in the air than on the ground. Mind you, on the ground I cannot go higher than 2000rpm...
Full rated power is not developed until the aircraft is in motion / flying. The De Havilland Dash 8 requires prop balancing to be accomplished in the air. Most aircraft props I have balanced were satisfactorily accomplished on the ground e.g. Mitsubishi MU2, Beechcraft 90, 100, 200, 300.
 

Magisterol

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Full rated power is not developed until the aircraft is in motion / flying. The De Havilland Dash 8 requires prop balancing to be accomplished in the air. Most aircraft props I have balanced were satisfactorily accomplished on the ground e.g. Mitsubishi MU2, Beechcraft 90, 100, 200, 300.
The vibration is not from an unbalanced prop. It is from the engine.
 

Magisterol

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Well, knock on wood, looks like the roughness is gone, with the replacement of the fuel nozzle. Still don’t understand why is started to happen all of a sudden. My only explanation would be that when the mechanic put the original nozzle back on somehow the hole or holes got messed up (unintentionally) and since then the roughness. Don’t know what to say.... Anyway, thanks everybody for the help. Cheers.
 
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