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Engine stumbles when advancing throttle

JimWoo50

Well Known Member
0-320 fp, carb, dual pmags. Happened twice. Engine performs normally in the pattern, but when I’m cruising at 2300rpm’s or so and advance the throttle with mixture leaned I get real rough running to the extent it feels like it’s going to quit. As soon as I pull back the throttle everything goes back to normal. I also enrich the mixture. At first I thought it was a slug of water in the fuel so I checked that after the first incident and there was none. I am of the opinion that there is a issue with the carburetor, the acceleration pump. But I am open to any suggestions.
 
Which model carb do you have? Does it have the “Mooney Mod”? Some carbs don’t have an accelerator pump..
 
how lean? Unlike an FI servo, the mixture adjustment on a carb sets total fuel flow, not a percentage of fuel needed based upon air flow. Therefore, if running lean of peak, you must richen the mixture before adding throttle, else you go too lean and stumble or misfire. If ROP, like the pattern work, the engine will go rich to lean instead of lean to too lean. If the accelerator pump was not working or mis-adjusted, it would be most noticeable as you push the throttle to WOT at takeoff. Small throttle changes equal a small acel pump shot. If your not stumbling as you push the throttle in at TO, it is unlikely that the acell pump is the issue.

Larry
 
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Thanks Larry

Just flew and did as you said and no roughness at all. Will try again next time just to further test when I can go a little higher as was 2500’ broken here at Bult.
 
Carb

All Marvel carbs for the 0 320 and 0360 should have an accelerator pump. Some of the early four cylinder Lyc carbs did not have acc pump. Those were M
a3 series.
 
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