Thorp Air Command - T18.net

I posted a while back about a problem I was having with my MA-4-5 carb flooding. At first I thought it might have been a water contamination problem and sent the carb back to Aero Sport Power for a look see. They replaced all the parts that were corroded and I even had them replace the float to include the SB for the new "blue foam float. Got the carb back, installed it engine run up ops normal. Shut down and came back out about an hour later and fuel was streaming out the bottom of the heat box ? Called ASP and talked to the head engine guy and he said it might be the needle seat. He looked at the seat when he replaced the float and it looked good so he did not replace it. I had a "quick build kit" on the bench that had a new brass seat and needle valve so I said I would replace the seat. Took out the seat and found FOD down in the opening on the outside of the brass finger screen. This must be the problem (jamming the needle valve?) and I removed the finger screen, cleaned it all out, put in a new brass neat and needle valve and set the float to specs. Put the carb back on, turned on the fuel and fuel was pouring out of the main fuel nozzle ? What the FARKLE ! Called ASP again and they said ship it back. A few days later they called and said they could not find the cause of the flooding ? They were shipping out a new carb. This "new" carb even has the SB (service bulletin) float installed. Put the carb back on, turned on the fuel no leaks. Start up and run were normal. Shut down and 15 min later fuel is AGAIN running out the bottom of the heat box. Exactly as before !

I don't get it. I've had the carb on and off 4 times. I don't see how fuel is getting past the needle seat ? I will call ASP again on Monday for advice, but anyone out there have an idea what the hell is going on. 20 seconds from a controlled ejection.

RB

Yes Sir. The replacement carb I got came right out of the box and onto the engine. Mixture cutoff goes from stop to stop with the cockpit control. Had to readjust the linkage (slightly) on the throttle to go stop to stop with the cockpit control. This is EXACTLY the same problem I had with the carb that came with the engine. Worked without a problem for 40 hours. This problem did not show up until I had flown 40 hours (not sure how it is related to to separate carbs?)

I would not think even if the mixture cutoff or if the throttle did not hit the stops that this would cause the "flooding?" I went out and turned on the fuel valve again and it is still dripping a steady stream from the bottom of the heat box. I applied the Air Force mechanics trouble shooting technique by using a small rubber mallet to the float bowl to see if it would free up the float (if that was the problem)...no workie. The first carb that had the problem I was able to see that fuel was comming out of the main fuel nozzle in the carb throat. I have not taken this carb off to see the source of the fuel, but suspect the same source. This is gettin old...been AOG in the drivway for a month now.

This carb has the new blue float as the data plate is stamped FF (Foam Float).

RB

Rich, call me, I had the same troubles and had to fix it myself.................Dan

Roger that Bro.

This may be far fetched, but does your primer have a leak? If the primer is lower than the level of fuel in the tank, then it could (maybe) syphon fuel through the primer lines and run out the intake manifold looking for all the world like a carb leak.

Most likely it is dirt in the system, however. Make sure the gascolator is installed correctly (input and outflow). If installed backward, you will bypass the screen. Shut the fuel off and inspect the gascolator bowl and screen prior to draining looking for junk in there.

Good luck!

_________________
Bob Highley
N711SH
SN 835
KLAL

Are you running auto fuel or avgas when you have the problem?

_________________
Bernie Fried
N18XS

Vans electric primer plumbed directly to the cylinders.

100LL all the time. So not a seal issue. This "new" carb was sent to replace the original one that came with the engine to correct the leaking fuel/flooding issue. Both carbs do exactly the same thing...leak fuel out the bottom of the carb. The first carb had the float, seat and needle valve replaced (among other items in the accelerator circuit). I would have to have real bad luck if this replacement carb has exactly the same internal issues. The first carb went 40 hours without this leak ? The replacement carb has the blue float as did the first carb.

RB

Flooding/dripping/leak is with the engine off. Makes no difference if the mixture control is full rich or idle cut off. Same with the throttle...leaks the same if full foward or at idle.

Sleepless in Seattle

If your positive you haven't got some alcohol ruining your carbs.
Do you have a fuel pump?? What Pressure?

No buzz juice, unless the Air BP pump with 100LL has it in it. Even if it did, not sure how 10 min. of fuel in the carb (and a new carb at that) would cause this problem. Yes...2 pumps. Standard engine driven pump and a Facet pump. Fuel pressure sender AFTER the engine driven pump. Max fuel pressure at any given time is 3-5 psi.

The leaking occurs with the engine OFF. Fuel valve ON and boost pump OFF. FWIW...gravity feed works just fine.

Just to go over the specifics about the flooding

1. Only fuel used has been 100LL from at the airport out of commercial sources. Calif. fuel.
2. First carb that came with the zero time engine worked perfect for 40 hours, then developed the leak...fuel dripping out the bottom of the air box after landing at KSEE and engine shut down crossing the numbers.
3. Sent the carb back to Aero sport Power and they replaced some corroded parts (water in the fuel), including a new blue float (per the Volare SB). Carb had white plastic float. IC# on the carb was #6.
4. Put the carb back on the engine and it ran fine. Shut the engine down and came back out 30 min. later to find fuel again dripping out the bottom of the air box ?
5. New brass seat and needle valve were not replaced when the float was replaced as they "looked OK." I put in a new seat and needle valve and set the float to manual specs 13/64."
6. Attached the carb to the A/C fuel line (did not bolt it to the engine this time), turned on the fuel valve and began leaking imediately just as before ?
7. Sent carb back to ASP and they could not determine the cause. Sent me a "new carb" (still in the Precision plastic bag), bolted the carb on and turned on the fuel. No leak. Turned on the boost pump. No leak. Started engine and it ran just fine. Shut down. Came back out in 15 min. and fuel was leaking AGAIN out the bottom of the air box ?
8. Fuel samples are clean. No dirt or water. Fuel is fresh. After having the water in the tank, it was drained and dried out and fresh fuel was pumped in.
9. NO alcohol in the fuel. At least none that I know of as it came from a commercial 100LL pump at the airport.
10. Fuel pressure as measured after the engine driven pump and before the carb. is 3-5 psi max.
11. Mixture and throttle controls go stop to stop.
12. Vans electric primer

1. I suspect it is a float level problem, but not sure how that can occur when a new float was installed on the first carb (I assume the float level was adjusted).
2. A new seat and needle valve were installed on the first carb (by me) and the float level was AGAIN adjusted to proper specs.
3. New carb arrived and has FF (Foam Float) stamped on the data plate indicating a new Blue float has been installed (at Precision) and it was properly adjusted. I "ASSUME" that part !

The only thing I can probably do before going to General Quarters is attaching a clear fuel line to the float bowl drain plug. Got this idea off the Vans site. They suggest getting another plug, drilling a hole to accept the clear fuel line the model A/C guys use and expoxy it into the hole and using it as a level see where the actual fuel level is in the bowl. Pretty much like the procedure in the overhaul manual, but not using the expensive "required" overhaul tools.

RB

I would check the fuel for alcohol just to eliminate it.
I got a cigar tube for the test tube. Add about an inch of water and mark the level. Add gas, cork an shake, shake, shake. If the water level rises above the mark, somebody messed up. Forty hours = one good tank of fuel.

Hi Rich
Any chance of teflon thread tape floating in fuel lines? Just a thought.
Brian

_________________
Brian

Brian: I only use telfon tape on shower heads. The only thread lube I use (if I need it) is the stuff called EZ-Turn. Comes in a tube. The only place in the entire fuel system where I used "a little dab will do ya" of the EZ-turn was on the threads of the 90 degree steel fitting going to the carb fuel inlet and I only put it on the last few threads. If there is teflon tape in this second carb, it came from the factory that way. I would hope the brass finger screen in the carb fuel inlet would catch any goo, gunk, birds nests, loose change before it got to the needle valve. Come to find out from the carb manual this screen is on the 100 hour annual for checkin. I know some folks have used the teflon devil on their gizmos and paid the price. I appreciate any and all input. I have been searching the web and the only thing that turns up regarding the flooding is the float (the old float) and possibly the needle valve. Being that I have the new float not sure where to go. Monday a few phone calls (thanks for the input Dan...I may have to resort to jerking around the float level adjustment) and try to see what the poop is with this carbeertator.

RB

Rich

My father had a similar problem with his tripacer
Leaking fuel from carb after an extended park time on ramp

Found fuel in carb bowl too high
Found it by hooking up the plastic tube to a 90 degree angle off back of carb and watching how high it came in tube

The thing was it ran the best and did not leak when fuel was kept at the same level as the "prop" on the side of carb. MA 4 I think??

A tech instructor said he heard the "prop" level was the correct sweet spot for fuel level

Just an extra tidbit of info

Hope you get her going

Paul Gagnon

Rich,
The there are two steps in setting the float level ...

1.) set the height visually (as you have done)
2.) the clear tube setup you mentioned above. If you do not do this step after rebuilding/replacing seat, float, needle your just making more work for yourself as you need to verify the float is seating before you bolt it on the a/c. One way or another your float needle is not seating or the float is not adjusted correctly.

The procedure is outlined in the ms overhaul manual but in short install a fuel source to the carb (I've used a suspended cup above the carb and a short fuel line) and then a clear tube at the bowl plug. Make sure you have head pressure i.e. After the bowl is full refill the fuel source (cup). Using this verify the correct level (just shy of the carb bowl split line). To readjust carefully bend the float tab arms (use two sets of pliers to avoid putting stress on the float itself)

That being said the past two carbs I've rebuilt took several iterations of the above as precision(now tempest) kept sending me defective needles/seats.

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD