sticky carb piston

[wukkie1]

hi, ive overhauled my twin cd150 strombergs one is slightly sticky on first lift up, would the vacuum initially lift it regards bill   (still a way off trying to start it

[thescrapman]

There should not be any stickiness at all.

If you lift it with your finger in the intake side, the piston should move up freely, then when you remove it drop slowly to teh bridge stopping with a distinctive "thunk"

try it with the damper out, then with the 4 screws loose on teh cover.

Cheers

Colin

[Clive]

Aha, I may know about this one. Although the top will screw down in any one of the 4 possible orientations, the piston will only move freely when it is the correct one.
I found this out by the side of the road. Spare diaphragm, tick. Incompetent, tick. Forth attempt lucky.

[Jonny-Jimbo]

Just had this trouble with a set of CD125's on a Ginetta. One carb was fine, the other would rise fine, one would stick not far above the bridge. Pulled them apart and found the needle was slightly off centre, so when the piston dropped the needle gradually increased pressure on the jet. If I took the damper out I could push it down easily.

Recentering the needle in the bottom of the piston, then recentering in the jet solved the problem.

[Pete Lewis]

you need to identify what is sticking,  the centreing advice is right , but have you taken the air piston out and checked it slides freely in its top cover  ??    carefull use with some oily flour paper will remove any old residue or corrosion.

are the diaphragm location lugs correctly located in the small relief in the air piston and the outer rim ?  is the diaphragm nice and supple not like an old inner tube , some after market ones are poor.

if the diaph. is distorted wash it in clean petrol it will revert to its correct size.

http://p38arover.com/misc_files/Tuning_Stromberg_CD_Carbs.pdf
some usefull reading  
Pete

[geharvey]

Hello,

I've had this problem before when I have taken the carbs apart. The needle sticks on the jet and jet needs to be centralised. If you wind the jet upwards until it touches the bottom of the air valve, loosen the nut that holds the jet guide in the carb body, then lift and drop the air valve onto the jet a couple of times. It should give a positive clunk. then tighten the jet guide securing nut. The air valve should now move freely. Good luck.

Graham.

[Ron]

I've also found that the pistons will stick if the top of the carb is screwed down too tightly onto the body. Loosen the screws and tighten them a little at a time to see if it makes a difference. My old carbs will probably have to have a rebuild, will probably buy the kits from Rimmers. Has anyone had any experience of doing this? Are they good value?