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Stuck lifting Pin on 1978 Midget Su Carb

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Len-Tikular George P
Denholm, ROXBURGH, UK   GBR
My Midget has all of a sudden become temperamental in stating. Repeated runs for a second or two then stops. Lots of fiddling with the choke and throttle eventually gets it going. I have noticed that the Idle RPM has fallen to 500 previously 800.

I discovered that the Piston lifting pin on one of the carbs is stuck, could this be the problem ? How do I free it up ?

Thanks


George

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bev sleet Avatar
bev sleet Bev S
Raunds, Northamptonshire, UK   GBR
It's not the lifting pin causing problems, you need to explain in more detail what you mean by fiddling with the choke and throttle before anyone can advise you .

hoggie Avatar
hoggie Mike Hogan
Oklahoma City, OK, USA   USA
By saying the lifting pin is stuck, are you saying the piston itself is stuck ?

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Midgies Dad Avatar
Midgies Dad Ben M
York, ME, USA   USA
If your lifting pin is stuck, it's time to remove and service or rebuild the carbs and see what else is going on that's causing the starting problem. Then they can be reinstalled and tuned per the Bentley (factory) manual and should then run well.

Len-Tikular George P
Denholm, ROXBURGH, UK   GBR
Lifting pin on one of the HS4 is fine, the other is stuck, I'm assuming the piston is free because when started the engine runs well. Looks like I'm goint to have to bite the bullet and take the carbs of for inspection. I'm just a bit wary about doing this as I have not done it before!

bev sleet Avatar
bev sleet Bev S
Raunds, Northamptonshire, UK   GBR
Ok before you do a total removal check the damper pot for oil, you should feel a small resistance pushing the damper plunger in, if there is no resistance put 5ml of ATF in the dashpot, if that is not the problem the next move is to take the 3 screws out holding the dashpot on and gently lift the bell and piston straight up (Do not bend sideways as the jet needle is fixed to the bottom of the piston) clean the piston and bell and re-assemble, check the needle is not bent. If nothing works then you got trouble, however there is a good tutorial on this site in the library in the black bar at the top of this page, also see John Twist video's on you tube as he duos a total strip down on carbs.
Good luck

Len-Tikular George P
Denholm, ROXBURGH, UK   GBR
Many thanks, dashpot oil is ok, so i,ll do as you say and lift the dashpot off,

Thanks
George

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Len-Tikular George P
Denholm, ROXBURGH, UK   GBR
Ok Bev S I found this,

"One other item now fined to all S.U. carburetters is the piston lifting pin. This is used when the engine is not running, to lift the piston assembly for the purpose of checking that the needle is correctly centred and that the piston falls freely. It is also used to lift the piston a small amount when the engine is idling in order to check the mixture strength."


So it seem as though it is not all that important after all! in that it's not detrimental of the correct running of the engine.

Regards

George

Len-Tikular George P
Denholm, ROXBURGH, UK   GBR
No! the piston itself is free to move.

Thanks

George

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bev sleet Avatar
bev sleet Bev S
Raunds, Northamptonshire, UK   GBR
George when you are trying to set idle speed you must loosen the two nuts on the linkage bar and do one carb at a time


















































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