Last weekend I had my first bout of vapor lock in the RV-4, so I read this discussion looking for info.
90 hrs SN Lyc O-360 with carb, mags, standard fuel system with selector valve just fwd of the stick, Facet just downstream from there in the center tunnel about a foot forward of the spar, and the gascolator on the lower firewall.
It was in the 90?s, and I had about 90% 87 oct auto gas in both tanks, 10% 100LL. First time I ever had more than 50% auto gas. I recognized that this may be the perfect storm so was alert to the possibility of vapor lock (it was gassed up on a cool day, if I had filled it this day I would have used 100LL). It started and ran fine, flew for 20 min, then shut down for about 20 min. Normally it starts great with no prime even when hot, but it started hard the 2nd time. Fired up right away but spit and sputtered about 10 sec before it ran good. Taxied fine (mixture leaned as usual), did a runup to 1800 rpm, ran fine. Then had to wait a few minutes for the runway. On takeoff, mixture forward and as soon as I got to about half throttle it started sputtering so I aborted. Repeated the process and it did it again so I put it away.
After reading all these posts I have a few thoughts.
A number of you suspect the Facet pump is getting vapor locked and purging the line will help. First, be aware of this?
Mine is mounted horizontal with respect to the airframe, but it?s a tail dragger so the outlet is higher than the inlet at least on the ground.
Second, rather than running another line and a purge valve (I prefer KISS), how about turning on the pump and draining some gas out of the gascolator to fill the line, pump, and gascolator with ?cool? fuel. Not sure how much volume you need to drain, but it can be dumped back into the tank or a lawnmower if clean.
Third, if heat is the culprit I?d like to add some cool. I got a fuel pump shroud but never installed it because it looks like a major job with all the junk in the way. Thought about putting blast tubes on the pump but had another idea? add a NACA inlet or slotted louver on the top of the cowling between the rear baffle and firewall. This would/might bring ambient air down across the rear of the engine and exit out the bottom. It should cool the entire rear engine compartment better? all the accessories, fuel lines, firewall. In addition, when you shut down the heat back there has a place to get out and you should have a flow of cool air entering the bottom opening and exiting the top. Negatives: Drag? Water? (electrical stuff on the firewall and soon to be installed dual P-Mags probably should not get wet). Thoughts anyone?