Thorp Air Command - T18.net

Since we are on the subject of fuel, I'll fill everyone in on what happened with my MA4-5 carb. After my almost off field engine out landing, I removed the carb. and sent it to Aero sport Power for a check up. They notified me today the acceleration check valves were corroded allowing fuel to siphon from the accelerator circuit all the time causing the engine to run rich. This is how it happened. During our wettest Winter in San Diego in almost 10 years, water had made it past the fuel cap O-ring. Prior to this I had back off the adjusting nut on the fuel cap to make it easier to remove ( O-ring too tight). This was a mistake as it allowed considerable water to enter the tank. The A/C was still in the driveway being prepared for it's first flight and after all the rain I decided to do a run up. The engine attempted to start, but that was all ? Then I decided to drain the sump. Why didn't I drain the sump prior to the start ? Well...nothing had changed from the last start, same location, no fuel added, did not suspect a misadjusted fuel cap. The fuel in the tester was "clear" and "clean" and I did not suspect any water. Tried another start, but no go. I again drained the sump and the fuel tester was again "clean" and "clear?" Something did not seem quite right. I again drained a sample and smelled the sample...no smell of fuel? I then held it up to the light and what should have been a light blue color was "clear!" It was 100% water ! At this point I knew water had made it to the carb, but did not suspect any real damage. I pulled the plug on the carb bowl and it was full of water. I then disconnected the fuel line to the carb and turned on the fuel pump and proceeded to pump a large amount of water into a bucket. This was not good. After I drained the carb, I drained the fuel tank of all the fuel and found maybe a cup of water in the fuel. After the tank was drained I cleaned and dried it out and put fresh fuel in the tank. The engine fired right up. The engine ran perfect for the entire 40 test hours, but I guess the damage was done and my luck almost ran out during hour 41.

Bottom line...I should have been suspicious of the "clear" fuel sample and now I always take a quick wiff of the fuel in the tester and verify the "color.". I will always drain the sump of all possible water prior to engine start. I know it is not possible to eliminate ALL water from the fuel, but I will come darn close.

I bring this up as a safety of flight for those with ill fitting fuel caps. I also plan to cover my fuel cap area during RON's to keep out the H2O. I have re-adjusted my O-ring to fit real snug.

RB
NX115RX

Rich,

Thanks for the thorough write-up. This was/is a real eye openner. I'm sure yours is a non-vented cap, however, others out there need to assure themselves that they don't use a vented cap without some sort of rain protection.

_________________
Bob Highley
N711SH
SN 835
KLAL

It is a non-vented cap. The mistake I made was relieving the tension on the nut on the bottom of the cap to make it "easier" to take the cap off and put it back on. I thought I had enough "load" on the cap mechanism to seat the O-ring...boy was I wrong! Aero Sport Power is going to rebuild the carb for the cost of parts. Bart at ASP is doing the labor for free ! BTW the carb has the plastic float, but not the one called for in the latest SBMSA13. I had them replace the float also to comply with the SB. If your carb has an IC# on the data plate below a #15, you should check the float to see if it is up to par.

I don't mind putting myself on report if it keeps someone else out of the weeds ! In 40 years this was as close to landing short as I care to be !

RB
NX115RX

The other reason to always wiff test the fuel sample. It just smells good - I like the smell of Avgas. All that smelling lead explains a lot.

_________________
Pat
N89SB
T-18W

I just have to retrained. I am akin to the smell of J-4/5 and letting the Crew Chief/Maintenance Control fur doing the fuel sampling stuff ! I can tell ya with certain that this fuel snafu won't happen again !

RB

Rich, I was surprised to hear about your near off-field. Very glad I wasn't in the right seat. I'm afraid that I would have been an additional distraction by making a heck of a fuss.

Thom
N551CM

_________________
Thom Steury
N551CM GOYAbird
KCNO

Not nearly as surprised as I was ! I should have the carb back next week and all will be well with the world.

RB

Thanks Rich, this one bothered me. The explaination makes perfectly good sence. I now have 160 hrs on the bird,and have yet to collect any moisture from the sump.This puzzled me as I always got a tad of H20 out of the Cessna tanks, but never the Thorp. Do you think this could be the culprit of some of the cases of engine stoppage on various aircraft?? An aircraft sitting for a prolonged pirod,H20 in the carb, then it gets sumped before takeoff, starts up and then floods shortly thereafter??? Sounds like a good possibility maybe even very probable in some caes where the Plane sits on the tarmac during bad weather. I just lost a friend in Santa Paula Sunday evening. Cessna, prop stopped shortly after takeoff, Killed him and his girlfriend both.........Dan

Dan: Sorry to hear about your friend. Always hard news to hear. Yes, I believe there may be many cases where water was a big factor in the fuel systems. Especially for those A/C that sit out on the ramp. Mine did not have water in it for an extended period of time, but just goes to show ya that any amount of time with the clear stuff in the fuel may cause the fan to stop. Thinking back prior to the incident, there were NO tell tale signs of failure. Run up was normal, takeoff power was normal...them Shazam ! A ruff runner !

RB