Ok, this is my first post on VAF. I’ve read through countless pages of prior forums and decided I need to seek more information from people much more informed then my self. Here’s the problem, recently installed an o320 A1A (overhauled) and have had two big issues. Issue #1 first flight the throttle worked fine until I pulled power at altitude and I could never get it back resulting in an “uneventful” on airport landing. Post flight with cowling off showed all linkages in tact and I did not feel a difference in flight trying to move it….felt fine. #2 the engine seems to run extremely rich. Like black smoke at static RPM rich (I am at sea level) DA here in the south can get high but this seems excessive. I have to lean very agressiey to get a smooth engine. Mag drop is 300 on the slick 200 on the P-Mag when it’s rough. Then completely normal when it’s leaned. The carb is a Marvel Shraeder 10-3678-12 (matches with what lycoming calls for). It was overhauled in 2024 and has sat unused since now. Idle mixture has been adjusted and is fine. What in the heck is going on!!!!!! No leaks found and everything is sturdy on the outside. Thank you all for your time
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Lycoming o320 excessively rich (please help :) )
- Thread starter MoonDog1
- Start date
I'd check the carb heat function. Then I'd talk to the company or person who overhauled the carb.
The first thing I'd check is the Float level adjustment. Pretty easy to do, look up or ask the specs for what your float should be set at and measure to see if it is...It sounds like it's set wrong at first blush...
Black smoke is definitely too rich. If you are full rich at idle and getting that kinda mag drop, the engine is not able to burn the excess fuel. Next thing I'd check is the jetting for the carb...honestly with what you've described, I would just yank the carb and send it to a reputable shop for inspection/re-overhaul. Somethings not right.
I'd also be inclined to check all sparks plugs. I prefer the fine wire type, but that's me. If by pulling power at altitude means you pulled it to idle and loaded it up in the air, I'm surprised it didn't just quit. And I'd check the air box/ filter while I'm at it...
These engines are pretty straight forward...Fuel, Air, Spark and Mag Timing are always the first places to sort out.
I hope that helps.
S.
Appreciate It! Going to have it sent away on Monday. I agree something is not right!!
Carb heat seems to function properly. But good idea
I’d imagine if the carb was overhauled in 2024 by AirPower it would be complied with! I may be wrong… but this all makes sense.
You didn't say. Is it off high or low. If it's off to the high side, then yes.
Please say high or low................It makes a difference.
It is high I believe since it sits at 8/32 and the book calls for 7/32. This is with the bowl turned upside down I will attach a picture momentarily
Yeah. The floats look about right. I would check the needle and seat next for any debris. If the needle leaks at all, it will run rich in the mid range and you will have to lean aggressively.
Hmm ok I will try that next. I read page 1-5 of MS manual…Bet yes it was set correctly with the rise. That is a good idea tho will try and measure that way right now.
Possible you have the wrong main jet installed.
That really could be the case. It was overhauled in 24’ by AirPower.
I am leaning in the direction of there being debris in the carb causing the needle not to seat...that being said, if it's that bad in flight...it should be running on the floor, while parked. As previously mentioned, if the float hangs up, same kinda bad...and if it only happens in flight and gets knocked off whatever perch its found, landing and taxiing can knock it back off...those are pesky problems to isolate.
Having it off and playing with it, will probably reveal the discrepancy.
S
Update: spent a good portion of the day trying to see if I could find a “smoking gun” I am not an A/P so bear with me! The consensus seems to be the float is within spec. I took some air pressure and put it through the fuel inlet and tested to see if any was leaking from the pin when the float is closed. Couldn’t feel air getting through. Then flowed when it was open. This was a very crude method IK. Carb is going back to AirPower without a doubt… but I like to know what’s going on with my airplane. Sucks seeing my -3 sitting in the hanger on such a nice day.
Most common reason for excessive richness on a carb is a leaking needle/seat or excessive FP, Second is the float height adjustment and third is a leaking accelerator pump check valve. This is not likely given the new condition. Float height is suspect as it is a human endeavor at overhaul and humans make mistakes. Needle seat issues can be wear or debris.
You can also look for debris in the main circuit air bleed at the top of the throat. This will cause significant richness.
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That measurement is done from the top, so that means the float is a bit lower than spec, so not likely the cause of the richness.
I would purchase a new or rebuilt carb with certified papers with the correct main jet as per LYC and install. Place your original carb on the shelf and you might save for another day to do autopsy. Something is defective in that rebuild ie main jet, leak around main jet, accelerator pump, check ball and spring in accelerator pump. Float and or float jet. It need a total disassembly.
