Brief O-320 roughness on ground leaves me unsettled

Bo1000 · #1 07-19-2015, 08:55 AM

Landed for refueling after a half-hour flight in 90deg weather. Fueling took about 20 minutes and the plane was pointed away from the wind. Sumped tanks, no contamination. Shortly after restart, the engine ran slightly rough and the only instrument indication was flickering of the RPM gauge (GRT EFIS). The engine smoothed out after about 15 seconds, and run-up was normal, so I flew home (30 mins) uneventfully.

What would cause this, and is it something to worry about?

Thanks,
Bo
20 hours into the RV world

RV Jerry · #2 07-19-2015, 10:25 AM

Probably vapor loc very common after hot start

Mike S · #3 07-19-2015, 10:28 AM

Quote:

Originally Posted by RV Jerry

Probably vapor loc very common after hot start

Without knowing more about your particular aircraft--------I have to go along with Jerry.

Tell us about the plane, engine induction and ignition systems.

Bo1000 · #4 07-19-2015, 04:41 PM

This is an RV-9A, 280hrs total on engine, carbureted, 2 Slick mags. I hope we're talking vapor lock, but the brief flickering RPM indication on the GRT made me wonder if it might be ignition-related. Thanks again.

petehowell · #5 07-19-2015, 06:03 PM

HI Bo,

Not to be flippant, but if the carbed O-320 in my -9A does NOT stumble on a hot start, I might think something is amiss. In my case, it is a touch of pneumatic lock, that I now easily managed with the mixture control. Once the fuel gets moving, all is fine.

The temps in the cowl get really hot on a turn like that and sometimes the gas just wants to boil a bit. It should be watched, but as the guys said, I'll bet that is what you are seeing.

Send me a PM if you want to talk about it in more detail.

f14av8r · #6 07-19-2015, 06:51 PM

Pete,
Would you expand your discussion of "pneumatic lock" please? I've been having a little trouble with my carbureted 0360 on a hot start and am interested in how, exactly, you are managing your hot starts with the mixture.
Thanks!
Randy

petehowell · #7 07-19-2015, 07:01 PM

Hi Randy,

Some good reading here:

If I see more than 3PSI on the fuel pressure before I crank a hot start, I know I will need to manually lean to keep the engine running. Once cooler fuel hits the bowl, she runs normally.

I did not come up with this, I learned from smarter people here on VAF......

rbibb · #8 07-20-2015, 05:50 AM

If it bothered you on the ground imagine it happening in the air.

Bo1000 · #9 07-20-2015, 02:20 PM

Thanks for the hand-holding, guys. I will assume my engine roughness was a not-unusual result of a "hot turn" and will attempt to minimize it in the future with early morning refuelings or, if later, have lunch while the engine cools back down; park nose into the wind; etc.

And PM to Pete Howell.

Bo