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MG TD TF 1500 - SU carb fuel loss

My SU's float pins fall with overnight sitting. I don't see any drips anywhere, and wonder if I could be leaking internally, and ultimately diluting my oil.
Any suggestions? This is probably and old topic, but I can't find it in the archives.
Bill Cole, Arlington Heights, IL, '53 TD
Bill Cole

Do you mean the tickler pins that go through the chamber lid? George
George Butz

Hi Bill, Next time you come back from a run and after shutting the ignition down, remove one of the dashpots and piston. Then look down into the jet, everything should be stable with the fuel level about 1/16" below the bridge. If you notice however, that fuel is spurting and bubbling out of the jet, then your float bowls have overheated causing the fuel to boil while the car sits idle until everything cools down. This will drain the float bowls causing the needles to fall until the next time you turn on your fuel pump. A heat shield might help to prevent this, as well as insulating the gas line from the muffler where it sits very close. Hope this helps. Cheers Phil
Phil Atrill

George: Yes, I am referring to the tickler pins in the cover of the float bowl.
Phil: I suppose it could be heat, as I just came in from a hundred mile run in 80 degree heat yesterday, however, last night,well after the engine cooled down, only the front carb pin was down. This AM, both were down. I'll recheck tonight.
Bill
Bill Cole

Phil has overstated the fuel height in the bridge (at least compared to what I set my customer's at) 1/16 could cause minor flooding out in tight turns as the fuel spills into the throat. I recommend 1/6 of an inch, or anywhere between .120 to .200 below the bridge. I usually try for .160

Also, boiling and spurting in the bridge is not usually caused by the float bowls heating up too much, but by the transverse arm between the float bowl and the carburetor body heating up. The volume of fuel in the transverse arm is MUCH less compared to the surface area of the aluminum than the same for the float bowl.


warmly,
dave
Dave Braun

Bill, read the "Sticky Tickler Pin" thread carefully. Sounds like your pins are sitting on the floats without the spring to hold them up. The pins shouldn't touch the floats unless you press them down. The gas level will gradually drop in the float chambers due to evaporation- the are not sealed, and are vented to the atmosphere through the overflow tubes, and through the jet area out the air cleaner. That is why the fuel pump clicks quite a bit when the car has been parked for a few days- the gas in the float chambers has evaporated. Unless the float level was set way, way too high, no way it could leak into the engine, as the gas level is set a touch below the jet bridge (as mentioned in the above posts)- it can't run up hill. George
George Butz

Thanks to all who answered. Seems I've got a bit of checking to do. Last nights experiment: Ran the fuel pump until the tickler pins were full out. Checked tonight and the front carb pin is still up, but the rear is down. No engine running to generate any heat
I'll try to find the stickey tickler pin thread.
Bill
Bill Cole

This thread was discussed between 24/05/2010 and 26/05/2010

MG TD TF 1500 index

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