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o-320 Lycoming needs primer to start in the summer

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Paul Eckenroth

Well Known Member
I'm looking for some input from the Lycoming gurus out there. I have an RV9A with about16 years and 1300 hours. Up until last year it would start instantly in the summer with no primer used and instantly in the winter with 4 seconds of primer. Last year it started requiring 2 seconds primer in the summer. Winter operation remained the same as previous. I figure that the change in primer required for summer operation indicates that a component is deteriorating. Once it starts in the summer it behaves normally with proper power and speeds. Plus fuel flow remains consistent.
I would appreciate advise on what I should check and what the likely culprit might be.
Thanks in advance.

Paul
 
Try engaging the starter and then pump the throttle a couple of times, from closed to 1/4 open. DO NOT pump the throttle except with the starter engaged.
 
Paul Eckenroth said:
I'm looking for some input from the Lycoming gurus out there. I have an RV9A with about16 years and 1300 hours. Up until last year it would start instantly in the summer with no primer used and instantly in the winter with 4 seconds of primer. Last year it started requiring 2 seconds primer in the summer. Winter operation remained the same as previous. I figure that the change in primer required for summer operation indicates that a component is deteriorating. Once it starts in the summer it behaves normally with proper power and speeds. Plus fuel flow remains consistent.
I would appreciate advise on what I should check and what the likely culprit might be.
Thanks in advance.

Paul
Click to expand...
A carb or fuel injected? Accelerator pump on the carb?
 
Walt said:
Time for a carb overhaul
Click to expand...
Thanks Walt. I am mainly interested in what equipment may have changed or deteriorated rather than technique to start the engine. If the carburetor is failing, what would cause the initial hard start followed by normal operation. I have never used the accelerator pump to start. When the plane was new the engine temps were high and the carb was sent back to Aerosport Power to modify the jet. The carb is MA-4SPA.

Thanks
Paul
 
Walt said:
Then you have a nonstandard setup of some kind. The Marvel carbs have a accel pump.
Click to expand...
are there any other ideas or is the consensus the carb. If it is the carb are there any thoughts on rebuilding at home vs on outside supplier. If an outside supplier, are there any recommendations. Thanks.
 
Walt said:
Then you have a nonstandard setup of some kind. The Marvel carbs have a accel pump.
Click to expand...
You were right.. for some reason I was under the impression that my carb didn’t have an accelerator pump. I confirmed today that you are right, it does have it!!
10-4164-1.
 
Paul Eckenroth said:
are there any other ideas or is the consensus the carb. If it is the carb are there any thoughts on rebuilding at home vs on outside supplier. If an outside supplier, are there any recommendations. Thanks.
Click to expand...
It could be something else, e.g. induction leak, impulse coupling/magneto, plugs, compression. The first post mentions 4 seconds of prime, so I assume priming is by the fuel boost pump and a solenoid valve into the primer ports (and not primed by the accelerator pump). So I don't think it is necessarily the carburetor but there is not enough other relevant data to suggest exactly what is the problem.
However, if carb hasn't been touched in 16 years then it may be due for servicing anyway. I got mine done locally and would have otherwise puchased an exchange unit from Aircraft Spruce. There are special tools required to overhaul a carb and it should be flow tested and not everyone is equipped to do that at home.
 
I agree with the last Paul's comment about a carb rebuild/overhaul probably being due just to age. Back in the last century, I rebuilt a lot of carburetors for cars that had just gotten dirty and gummy. A rebuild (which was cheap and easy then) brought the carb and the engine back to life. Even if that's not the problem, a little TLC shouldn't hurt. Induction leaks would be next on my list to check. The hose connectors and gaskets on the inlet pipes are often problematic.
 
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