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O320 hiccup

RVGeorge

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I have a RV6 with a O320 Lyc with a fixed pitch prop that occasionally hiccups while reducing power from about 2240 RPM to approx 1800 RPM to about 2100 RPM range. Carburetor is new rebuilt M/S MA-4SPA purchased from M/S. The spark plugs were replaced about 40 hours ago. Mags and spark plug leads changed 150 hours ago. I try to lean the mixture on the ground. Mag drop normal. A/C based at KTOA.
Thanks for the help.
 
I have a RV6 with a O320 Lyc with a fixed pitch prop that occasionally hiccups while reducing power from about 2240 RPM to approx 1800 RPM to about 2100 RPM range. Carburetor is new rebuilt M/S MA-4SPA purchased from M/S. The spark plugs were replaced about 40 hours ago. Mags and spark plug leads changed 150 hours ago. I try to lean the mixture on the ground. Mag drop normal. A/C based at KTOA.
Thanks for the help.

I have had a similar issue here and there when reducing power in the pattern. I found it would get worse with higher heat-range or old plugs. I have since put in new intake gaskets, intake couplers, plugs and have also added Electronic Ignition on one side. It still happens sometimes, but not all the time and to a lesser extent, just a slight stumble.
 
Fuel nozzle

Had the same issue with my 4. It's the fuel nozzle, I think this is the correct name,. In the carb theres two different nozzles that can be installed. One has much finer fuel holes or orifices to help atomizer the fuel. The other one allows the fuel to puddle in the intake tubes, when you change throttle the change in pressure causes the fuel to dump into a cylinder making a over rich condition causing a hiccup. Change that part will fix the problem.
 
Hiccup

I have the same engine/carb in my -9A and have a similar stumble going through 1300-1500 RPM, both ways. This is the transition speed between the idle and main jet circuits in the carb. The carb was newly rebuilt. I sent it back and was offered a different rebuilt carb with the same part number. It is better, but still stumbles slightly. It seems to run rich, so pulling the red knob a little even at low altitude seems to correct the problem. I only use full rich mixture for climb out and landing. No stumble.
 
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