RV-9 Lycoming O320-E3D Vapor Lock

[StefanV]

Hi guys, my home field is 5500' AGL, and had temperatures around 89 degrees this past saturday. I gave 8 rides in the space of 3 hours, and with the last two got vapor lock in the system (engine is a standard carb O320-E3D). I run avgas exclusively, so was a bit surprised to see it happen. After having read the forums, it seems a return line to the one tank will do the trick. Any other suggestions, i.e. return line, and fuel pump shroud, sam james cowl etc etc. Also see guys refer to an article Van published a while back on this issue, does anyone have the link to the article? Any advice will be greatly appreciated! Thanks, Stefan.

[bkthomps]

vapor lock or you dumped the contents of your carb bowl or had fuel starvation at your pickups?

[StefanV]

Was strange start up was normal, run ups were normal, but as soon as I went past 2000RPM it started spluttering. The mixture was correctly leaned out for the higher altitude.

[Vlad]

Originally Posted by StefanV

I did 8 flips in a row, and with the last two got vapor lock in the system (engine is a standard carb O320-E3D).

Stefan what do you mean by 8 flips?

[StefanV]

Flips is the word we use for rides! So 8 cycles essentially start up/shut down

[Vlad]

Copy. I thought it was a simple aerobatic maneuver.

[N427EF]

I am not at all sure that your problem was vapor lock in fact I am quite certain it is something else.
Fuel starvation is my guess. This may not necessarily mean that your tank was empty but perhaps your mixture control cable might have moved or the rod ends on the cable started turning thereby leaning out the mixture to cut off fuel flow.
You said " the last 2 flights"? You continued flying by reducing power below 2000 RPMs? The same exact thing happened on both flights?
Mixture was properly set for the altitude? By what means, EGTs or an inch out on the mixture control knob or something like that?
Did you shove the mixture back in when the engine sputtered or manipulated the mixture at all?
Check the simple stuff first before you start modifying the fuel system.
More info please and someone will be able to help.

[StefanV]

Got A&P to check all the linkages etc, no snags there. Went and flew the plane afterwards, no problems whatsoever, so I still suspect vapor lock was the probable cause on saturday. Going to install a vapor return line to the left tank, not a big mod and should solve the problem in the long run.

[Walt]

Here's a pic of the system I installed when I had the carb installed. Used a standard primer valve as the "purge" valve and plumbed the return to back to the tank. I could always tell when I was vapor locking by the sound the little facet pump would make. Worked like a charm. I now have AFP FI and use their mechanical purge valve.

[N941WR]

Are all of your fuel lines insulated?

When I first flew mine, I did not insulate the aluminum line that went from the Gascolater to the fuel flow meter and that gave me some "issues". After insulating that line, no more issues.

Ive done 10+ "flips" w/ YE's on a 90+ degree day with no issues.