Thorp Air Command - T18.net

Paul and Lee: Incorrect float level is what I have suspected, but being that I received a "new" carb (even was in the Precision Airmotive plastic bag) this almost seemed impossible. Dan also led me to the float conclusion after I talked to him on the land line. The one thing that has kept me away from "readjusting" the float to other than the called for 13/64" spec is the Caution in the overhaul manual..."Under no circumstances change the float level from the established setting to correct flooding or to change fuel level."
"If fuel is observed running out of the nozzle, the bowl and throttle body must be separated and the float valve and seat cleaned and replaced." Well that was certainly done on the first carb (float and seat/needle valve replaced) and it made no difference in the flooding.
After 20 years as a Navy pilot, when I see the word CAUTION in a manual it can lead to undesirable consequences if not adhered to, but in this case after 3 gents have verified my suspicions about the flooding, I am off the the hardware store and then the model airplane store for some fuel line. Thanks for the help and advice guys !

"Prop" on the side of the carb ? I'll have to take a look at that.

RB

Rich,
I would pull the carb and test it on the bench, I'd be willing to bet this is not a float level thing but a needle seat issue ... like I said, last time they sent me 3 different needle/seat sets before getting it right.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

As You say you got a plastic float. Years ago we got rid of all of them and put back in the brass float, as modern fuels attack the foam floats. In other words they absorb fuel and get heavy. Not good.

Cotner

*** admin posted for Gary Cotner ***

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Forum Administrator

In idle cut-off there should be no fuel getting past the mixture control. On a C150 I found the mixture valve was not quite pinned in the right position and would not shut down cleanly.

*** admin posted for Hurant Karibian ***

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Not really plastic or foam. That's what they say it is, but it is really an epoxy float. Solid construction, not hallow like the metal/white plastic floats. Will not absorb fuel. There is a You Tube video (put out by precision I think) that explains the "new float. Very interesting.

RB

That's what I am going to do. Got all the fixin's to set up the external float level checker...clear tubing. Will advise what I find out. This sittin in the driveway is gettin old !

RB

Update on my carb problem. I drained the bowl (with the carb on the engine) and found nothing in the fuel, so I put the plug back in, turned on the fuel and the boost pump...no leak. Started the engine and shut down, no leak. Ran the engine 4 times with no leak on shut down...hum? Why was this new carb (out of the box) leaking before ? My time as a Maintenance Officer sez pull the carb (even though it "checks good on deck") and take a look inside. Before I pulled the carb I attached the external float level checker (clear tube) to the drain and marked the fuel level location. I then pulled the carb and split the bowl. The fuel level looked good. In fact as Paul had suggested, the fuel level should be at the level of the "prop" on the outside of the carb and it was ! I then check the blue epoxy float for any signs of rubbing on the bowl...none observed. The float level was checked and was spot on at 13/64." Pulled the needle valve and checked the brass bore for debris. Both the needle and bore looked OK. Pulled the brass finger screen and it look clean also. Looking in the bottom of the bowl I did find some sort of FOD by the drain. It looked like dried Permantex or maybe gasket material? There were also a few other "brown" particles in the bottom of the bowl. Could not ID what they were, but it is possible they were blocking the needle seat causing the flooding and when I initially drained the bowl they came loose ? Cleaned out the bowl, finger screen and made sure the seat was clean then put it all together and back on the engine. The last two days I've made 8 engine runs (with the boost pump on...6 psi) and shut downs and have had no leaks ! Not even a drip. [:D] Next stop the airport and a test flight.

RB
NX115RX

Hi Rich im a newbie, met some of you at oshkosh and the thorp wet bratwurst cookoff
anyway i have been lurking reading of your carb from this last post i would go further back
and look for residue in gascolator to find if there is more stuff that may come down the line
if you have one. my 2 cents worth


Larry webber/dennis lambert n335bw

*** admin posted for Larry Webber ***

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Forum Administrator

Thanks Larry: Yep...did that. The ye old gascolator is clean as was the finger screen in the carb. I've done 12 engine run ups with no leaks, so it either had to be the FOD I found in the float bowl OR during transit in the UPS truck (only kid glove handling here) from Vancouver to San Diego causing the float/needle seat to possibly stick. If the carb body were clear it sure would make trouble shooting easier !

RB

Rich, I rebuild updraft Model A Ford carburators and devised a test kit for float level check using a large glass jar. Cutout the lid to bolt to the top flange, (remove the bowl), screw the lid to the top half, screw on the jar(any size) connect the gas line and watch the action of the float, needle and seat, etc.

Bill: I could use that set up for the MS carb on my 8N tractor ! For the MA-4-5 carb I used a clear fuel line and a barb fitting to screw into the bowl drain, turned on the fuel and watched the level of the fuel in the tube. Similar set up to the overhaul manual, but they use a glass tube ( I left all my glass tubing back in HS Chemistry !) This method verified the fuel level in the bowl (wet fuel level line showed up inside) when I cracked the bowl.

RB

Rich - Found a great article describing the workings of the MA4. It never addressed your specific problem, but it is great background information.

http://www.kellyaerospace.com/articles/ ... ry_AMT.pdf

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In theory, theory and practice are the same. In practice, they are not.

Dick: Found this article doing my research. Very informative. FWIW it is uncanning how similar the MS carb is on my 1950 tractor to the MA-4-5 carb on the A/C. The only BIG difference is the accelerator circuit on the MA-4. Both carbs can use a gravity feed fuel system. Both have a similar exterior profile.

RB

I hate to beat a horse, especially a dead one, but here's another great Schebler resource.

http://home.comcast.net/~r123rs/Documen ... Manual.pdf

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In theory, theory and practice are the same. In practice, they are not.

Yep...got that one too. Between the carb manuals, engine manuals, my avionics manuals I've got enough bathroom readin material to last months ! [:p] Amazing what you can find online.

RB