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02-20-2011, 07:04 AM
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Join Date: Apr 2006
Posts: 117
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Vapor Lock???
Need some input,I flew last weekend and had this happen and it happen again this weekend. So here goes I live in Florida so temps are a little warmer, First takeoff, climb, leaning doesn,t seem to be any problem on Mogas. I run one tank Mogas the other Avgas. I also land on the Avgas tank to purge fuel system of Mogas. After landing I always open oil door. Then both times I was on the ground 3 to 4 hours. Now after startup on Avgas and run up takeoff no problem but on climb out I switched to mogas and then get Low Fuel PSI warning. Turn boost pump on PSI comes up but engine is still runnng ruff.
Lean a little to see if this helps, doesn't. Start to turn back to airport I had just passed, running that bad. Switched tanks back to Avgas while leaving boost pump on and in a minute engine smooths out turn boost pump off PSI steady,didn't touch a thing all the way home. So I read the VAF and think could this be vapor lock when I switched to the mogas on climb out with the engine hot? I have an RV-9A 0-320 Carb with firewall mounted fuel pump everything per plans, plumbing, gasolator. Maybe I should try to switch to Mogas after leveling off and things cool down in the engine compartment. What do Ya'll think?
__________________
Brent Mayo
Fernandina Beach, FL.
RV-6, RV-9, RV-9A, Onex, Panther
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02-20-2011, 08:16 AM
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Join Date: Feb 2005
Location: Chesterfield, Missouri
Posts: 4,514
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Quote:
Originally Posted by mayo3808
Need some input,I flew last weekend and had this happen and it happen again this weekend. So here goes I live in Florida so temps are a little warmer, First takeoff, climb, leaning doesn,t seem to be any problem on Mogas. I run one tank Mogas the other Avgas. I also land on the Avgas tank to purge fuel system of Mogas. After landing I always open oil door. Then both times I was on the ground 3 to 4 hours. Now after startup on Avgas and run up takeoff no problem but on climb out I switched to mogas and then get Low Fuel PSI warning. Turn boost pump on PSI comes up but engine is still runnng ruff.
Lean a little to see if this helps, doesn't. Start to turn back to airport I had just passed, running that bad. Switched tanks back to Avgas while leaving boost pump on and in a minute engine smooths out turn boost pump off PSI steady,didn't touch a thing all the way home. So I read the VAF and think could this be vapor lock when I switched to the mogas on climb out with the engine hot? I have an RV-9A 0-320 Carb with firewall mounted fuel pump everything per plans, plumbing, gasolator. Maybe I should try to switch to Mogas after leveling off and things cool down in the engine compartment. What do Ya'll think?
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It's that time of the year when winter blend mogas can cause trouble. The blend is different than in the summer season.
If you have a Hodges tester, check the vapor pressure of your mogas. I have found it most unacceptable this time of the year and drained it.
__________________
RV-12 Build Helper
RV-7A...Sold #70374
The RV-8...Sold #83261
I'm in, dues paid 2019 This place is worth it!
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06-09-2011, 12:05 PM
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Join Date: Mar 2005
Location: Olathe, KS
Posts: 374
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Paul,
Not to revive an old thread, but did you ever resolve this issue? Did "burping" the primer valve help?
I have the EXACT same issues as you where I beleive it is the FACET pump that is locked. It has occurred twice on me on quick turns in the heat.
Thanks,
Scott
7A
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06-09-2011, 09:18 PM
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VAF Moderator / Line Boy
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,256
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Quote:
Originally Posted by tx_jayhawk
Paul,
Not to revive an old thread, but did you ever resolve this issue? Did "burping" the primer valve help?
I have the EXACT same issues as you where I beleive it is the FACET pump that is locked. It has occurred twice on me on quick turns in the heat.
Thanks,
Scott
7A
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Actually, the weather got cooler, the problem went away, and I forgot about it. Now it is hot again, but I have removed my primer system, so can't burp the valve - lost that chance to give it a try..... 
__________________
Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
http://Ironflight.com
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06-11-2011, 10:24 AM
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Join Date: Feb 2007
Location: Ft. Atkinson, WI
Posts: 66
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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?
The fuel pump should be mounted with the outlet above the inlet. This will help with eliminate vapor lock issues. Never located the pump so the outlet is below the inlet. Horizontal mounting will not effect fuel delievery performance. http://www.facet-purolator.com/index...d=12&Itemid=83 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?
__________________
Bob Reiff
RV-4 N214RR Lyc 360, CS, P-Mags
EAA Life Member
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06-13-2011, 06:19 AM
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Join Date: Aug 2006
Location: Taylor Texas
Posts: 811
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Let's not re-invent the wheel
Fellas:
Experimental folks have been working with MOGAS for quite a while now - before MOGAS STCs were developed. I recall a tip from a fella I learned about in the 80s - he installed a tee at the carb fuel inlet and ran a line back to the tank. A .040 orfice at the tee kept the FP high enough, abut allowed any bubbles to go back to the tank. I do not recall if the tee has to be clocked so the return line was 'up' or not, but it might be a good idea. I expect this worked more or less as a purge system, but it was 'pilot-proof' as it required no input from the operator.
My guess is that the vapor line could be run into the selector valve with the same results.
Carry on!
Mark
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06-13-2011, 09:10 PM
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Join Date: Oct 2005
Posts: 1,516
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Mark,
I have used this very system in my 8 although fuel injected.
The idea behind the constant return fuel line is a constant flow of cool fuel
to the fuel pump as well as an escape for vapor bubbles.
The T can be installed at the carb inlet or at the fuel pump outlet with the same result.
A # 40 hole seems a little large, on mine I drilled a #68 and tested it at 25 psi
where it would return exactly 9 gallons per hour.
You are correct in saying that it does not need any pilot input, however if you plan on using mogas in one tank and 110LL in the other you probably want to return gas to the same tank where the fuel came from so as not to dilute your 100LL.
Andair makes a valve for just this purpose or you can solve that problem with a separate return valve.
I have never had a sputtering or rough running engine on the ground or in the air and I believe it is because of this return line.
The installation adds a little complexity and requires accurate fuel gauges to keep track of the fuel quantity but it also adds a few options to fuel management.
__________________
Ernst Freitag
RV-8 finished (sold)
RV-10 Flyer 600 plus hours
Running on E10 mogas
Don't believe everything you know.
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