Sticky Piston on Stombergs

[Darren Groves]

Twin CD150's on a MK1 Vitesse that's been standing for some years. Carbs seem to have been professionally refurbed but a long time ago.

 

With the air filters off, if you try to lift the pistons it takes some force to get them to rise, they jerk free and you can lift them freely, but then the don't return down again.

 

I've cleaned both, and the piston moves freely with the top off and if you just rest the top on the carb body it again moves freely, as soon as you tighten the 4 screws to secure the top it all stiffens up. It's the same on both carbs.

 

Any ideas?

[Simon]

Have you tried turning the cover round in one of the other 3 possible positions, this fixed it on mine.

[Roger]

Turning the cover round helped for me, and the amount of torque applied to each of the four screws also seems to have an impact. Have you tried to loosen one screw a little bit at a time to see if that helps?

[Pete Lewis]

have you centred the needle ??

 

the small  pointer arrow on the casting is to get the writing the same way round. & generally faces engine 

   these  caps where mass produced and not selective for any assembly tolerances 

 

         over years of tightening without some equal sequence and often very overtightened they can get distorted

 

              use a flour paper to sand any rough marks on the shaft  or bore , the fit is not that critical  so long as its free( like you want) but able to

      seal /hold the vacuum .

[juppy]

I've had this with a newly rebuilt CD150 carb on my 1300CC engine, I found just tightening up slowly and evenly seemed to make the difference, it took several tries to get it not to stick!

[Darren Groves]

Thanks for all the input. Turned out to be a bit of a tease, but got there in the end. It was the top cover causing the problems and I'll explain the method I used, just in case it helps someone else out at some point.

 

With the piston and spring in position put the top cover on and put the 4 screws in loosely and make sure the piston moves up & down freely. Start to tighten one of the screws whilst moving the piston up and down, once it becomes slightly sticky go to the diagonally opposite screw and tighten that one, you should feel the piston free up again, keep going until it becomes sticky again and then tighten the first screw a bit more. Keep going back and forth on the 2 screws until they are sufficiently tight and the piston is moving freely. Repeat this process with the other 2 screws and hey presto it works as it should....

[daverclasper]

Been doing that a lot lately.

 

As you say, bit at a time and seems to get there

 

Dave