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TechManSteve, ASE Certified Master Technician
Category: Ford
Satisfied Customers: 147
Experience:  My automotive and engineering experience is based on Fords. I cut my teeth on a 1970 LTD
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LE..leaking..both the dashpot and the needle assembly I..tool

Resolved Question:

On my 80 MGB LE I was attempting to remove the o ring that preventsdashpot oil from leaking but upon removal of both the dashpot and the needle assembly I do not find what the manuals show!. Unless the o ring has disintigrated and a circlip is gone I dont see what is wrong. I did use the proper tool to get to this point. Sy Kahn
Submitted: 9 years ago.
Category: Ford
Expert:  TechManSteve replied 9 years ago.
As many older Leyland cars were converted from Zenith/Stromberg carburettors to SUs, can you either check the markings or describe whether the damper is the dry piston type, or if it uses a rubber diaphragm between the piston and body. They work similarly but the actual bit and pieces differ.

Where is your oil leaking? The centre hole of the stem is hollow for venting the chamber. Oil here usually means overfilling.
Customer: replied 9 years ago.
Reply to TechManSteve's Post: Thanks for your response. This car was not used since last summer and would not startnow. Howeverafter correcting a bad(split) fuel intake hose, a new fuel filter and some tightening of carb screws, etc. I rechecked the damper but there was no resistance when droppinthemain carb piston. The oil level in the dashpot was nil, so I added some. After several hours I tried restarting and it fired but ran on 1 or 2 cyl. and slowly died. More fuel did not help. The book I am using says hard starting can be a symptom of oil leakage and the sealing o ring must be replaced in the area of the needle assy. with the needle assy removed one should be able to puse the o ring and circlip out of the big piston assy thru the threaded center hole but that seems impossible and I dont see any o ring. I must be missing something. The manuals do not explode the needle assy nor the center part(s) of the big piston that holds it. The parts lists also offerno help. Note that the intake carb fuel port is aft of the body but phots show it forwrd so I beleive there were minor carb changes not listed for early '80 production.
Expert:  TechManSteve replied 9 years ago.
Still looking for an answer which carb your car actually has. As I said, many late '70s emission type carbs were removed for other versions. This may very well be why the description does not match what you see. I'll assume that the single carb sutup remains, as you did not mention multiple carbs.

Did you feel some resistance in the damper after adding oil, or was it still lifting freely? With non-use, there is a good likelihood that you have fuel bowl filling problems in addition to some of the other quirks of the sidedraft carb.

Take out the damper rod and put it someplace clean. Remove the four screws holding the upper chamber in place and lift it off. You will see eitehr a piston with a machined large end with grooves in it, or a rubber bellows/diaphragm held by a plastic disc screwed into the aluminum piston. If it is type two, inspect the bellows for tears and holes.

You can lift the piston / metering rod assmbly out of the carb and set it aside. Look straight into the hole that the long metering rod entered and you should see fuel partway down (the tip of the metering rod may be wet with gasoline. If you cannot confirm that there is fuel in the bowl - this will have to be addressed first as it would clearly explain your no start condition.

The piston should move freely in the carb body when you lift or drop it. You may now reinstall the top chamber.

Let me know what you find in each of these steps and we'll go from there.
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Customer: replied 9 years ago.
Reply to TechManSteve's Post: The dashpot rod/piston was dry and it did drop freely. It has been removed as well as carb piston and diafpragm. Also the needle has been removed. I have a rebuiold kit if needed and thought that oil was leakinginto the carb and that an o-ring was shot. Ido not see that o-ring. Bear in mind the engine did fire but would no run for more than a feww sweconds each time.
Expert:  TechManSteve replied 9 years ago.
I understand that the dashpot was dry when you returned to the car after it had been sitting unused. My question was how well the dashpot worked after you put oil in it. From your wording, I suspect that you may misunderstand how the dashpot should work. Its job is to slow down the lift, not the fall of the piston, to slow the airflow on sudden changes in throttle opening. In the more common downdraft carburetor, a mechanical pump is used instead to momentarily add fuel to the airstream when the throttle is opened suddenly.

The only o-ring that I know of (now that you have confirmed which carb your car really has) is on the dashpot centre cap. It's not a functional part of the dashpot, its purpose is create a vacuum tight seal above the diaphragm.

The engine running for only a few seconds could be that there is insufficient fuel in the bowl (the reason for asking you to look for liquid at the discharge jet), inoperative damper (lifting too quickly), inoperative choke caused by ruptured diaphragm
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