Carb HELP!

LarryT · #1 07-28-2009, 09:36 AM

I have been working on a new-to-me -6A trying to take care of minor squawks since it was delivered in late May. Trying to get ready for a trip to Oakland to visit my sister and brother (who is visiting the US for the first time in 10 years). I am running out of time for this trip and have already missed a previous trip to San Diego and had to go commercial.

ONe of the issues was a leaking carb, MA-4SPA 10-5217, which I disassembled, checked the float (OK) and replaced the needle. Reassembled, turned on booost pump and no leaks. Fired up the engine, went for a test flight, stayed in the pattern, made three landings taxied in. The engine would NOT shut off with the idle mixture cut-off.

I operated the mixture control from the cockpit and the mixture control lever on the carb ran smoothly from stop to stop. I removed the carburetor and float bowl AGAIN. The mixture control is a rotary valve - a tube with a window in it that is covered/uncovered by the semi-circular brass piece connected to the mixture control lever. Is it even possible for the rotating internal part to become misaligned with the window in the tube??

Help I am truly at a loss for what to troubleshoot! Much longer and I will be forced to fly commercial to Oakland (an especially horrible fate when one is 6'4" tall) AGAIN.

LarryT

PCHunt · #2 07-28-2009, 10:14 AM

It is possible to reassemble the carb and fail to get the mixture shaft back into the tube in the bowl. As you put the bowl back on, be very certain that the "springy" mixture control shaft makes it into the tube.

LarryT · #3 07-28-2009, 03:51 PM

Pete-

I think that may be the problem. This AM I removed the carb and took it in to work. Determined that after the accelerator pump piston was in the pump well, I could not align the brass part with the steel tube. I had to use a screwdriver and flashlight to guide it into place.

this evening I will reinstall and report the result. Thanks for your assistance,

Larry

Brantel · #4 07-28-2009, 04:44 PM

It is very very easy to miss the socket that the mixture arm goes into when reassembling the carb.

98% of the time this is the issue when someone has had their carb apart....

LarryT · #5 07-29-2009, 01:10 PM

As you all correctly surmised, I didn't have the brass portion of the rotary valve inserted into the ID of the steel tube.

The 180 degree cut-out in the brass tube is on the right hand side as the carb is installed. Without guiding it into place (my ignorance), the close-wound spring shaft allowed the brass piece to deflect to the left, outside of the steel tube. It was necessary for me to use a flashlight and push the brass piece to the right in order for the brass piece to align with the steel tube ID as I reassembled the carb.

I feel somewhat stupid, but on the other hand, it must be ignorance because ignorance can be fixed, but stupid is forever!

Thanks for your help! Now I am really looking forward to flying to Buchanan Field to visit my sister and brother (who is back in the US for the first time in 10 years) and then on to Tucson to visit my 89 year-old father.

Larry