lycoming yahoo group
This just came up on the lycoming yahoo group. Some good post. Of course there is "
mandatory" Service Bulletin on replacing the old plastic floats with metal, dated 10/15/90, rev 11/11/91. The compliance is immediate.
http://www.precisionairmotive.com/Publications/MSA-1 Rev1.pdf
If you don't have MF stamped on your carbs data plate its probably the old plastic one.
I always thought the floats would sink slowly and thought you'd notice tell-tale symptoms, like rough rich idle and fuel dripping our of the carb, before complete power loss. Apparently not true as an experienced A&P informed me. Some floats, plastic and even metal included can just sink overnight or faster than that.
The history of Carb floats in airplanes is convoluted:
first metal (30-40's),
than plastic,
then metal again,
now plastic again.
There is a new plastic/composite/foam float. If you want the latest info call Precision Airmotive Corp., Everett Washington state, current owner of the Marvel Schebler and Bendix line of Carbs and FI.
Metal can wear and crack or leak. Plastic can absorb fuel and sink, even contaminate the fuel with bits and pieces. Apparently old poly floats would sink, but after you dried them out they would work fine? Interesting, but I would not recommend it, just interesting info I got from an old hand.
Kelly Aerospace fuel systems also makes PMA parts, including metal parts for Carbs as well.
Possible symptom of sinking float (from Sacramento skyranch):
Mixture to rich or lean. If mixture is too lean the engine stumbles on power application. Lean engine if mixture is too rich. Engine will smooth out and pick up rpm as it is leaned. After mixture is set, re-adjust idle speed. A rich mixture may backfire (more technically, inlet charge combustion). Rich idle, black smoke, and fuel dripping out carburetor is a sign that the fuel level in the float bowl is too high or fuel pressure to the carburetor is too high. Possibly the carburetor float is sinking.
New Precision Airmotive floats with install kit are about $160-$185, comes with new clips, gaskets, seats and misc parts. You can get the old metal float kits for less than $100 (Probably Kelly/Consolidated PMA parts)? Choice is yours. From what I am told the new floats should not suffer sudden sinking, since they have foam cores that don't absorb in or decay from fuel, so they say. May be we will have round 6. I feel bad from precision since they get sued constantly from all the years of old parts out there and people that don't accept the risk involved in flying and some responsibility.
Here is some good free info for Carb engine drivers. The new new NEW ones came out in 2005/2006 are now a plastic/composite w/ foam core. The "poly" floats that came out about 2002 are already outdated and obsolete. The metal floats are still in play (I think). If getting new floats, I think I'd go for the new non-metal design? Apparently its sink proof and tolerant or resistant to fuel degradation. However I don't know if its officially auto/mogas fuel approved? Don't do auto fuel myself. I do think they tested it for all kinds of fuels. Its only a matter of time till we know if this is the last type of float. Metal is pretty good but not prefect either.
New float large carbs (O360) & installation
http://www.precisionairmotive.com/Publications/SIL MS-15 Rev1.pdf
http://www.precisionairmotive.com/Publications/E-1002 Rev1.pdf
New float small carbs (O320) & installation
http://www.precisionairmotive.com/Publications/SIL MS-11 Rev1.pdf
http://www.precisionairmotive.com/Publications/E-1000.pdf
General INFO (GOOD STUFF)
Troubleshooting
http://www.precisionairmotive.com/Publications/MSATC-2 Rev1.pdf
Installation troubleshooting
http://www.precisionairmotive.com/Publications/MSATC-1 Rev3.pdf
Float Carburetor Handbook & Troubleshooting Techniques
http://www.precisionairmotive.com/Publications/MSAHBK-1 Rev1.pdf
