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Stromberg CD 150 help please!
prawnabie - 28/9/16 at 12:27 PM

Hi all,

I have a 13/60 Herald with a single CD150 on that I have just replaced the diaphragm on but I think that the piston is sticking as I can only get the metallic "click" of it hitting the casting when I flick it up against the diaphragm quickly so it comes back down with some force. If I lift it up with my finger and let it go, it stops about a mm or 2 away from the bottom of the carb body. Also, if the piston is lifted up too far, the diaphragm will turn inside out and the piston need to be pushed back down through the dashpot damper hole.

The above all happens whether the entire jet assy is in place or not, the piston also isn't binding on the body anywhere. The diaphragm is also installed correctly with the tabs lining up with the holes in the carb body.

Does anyone have any experience of this???

Thanks,
Shaun

r1_pete - 28/9/16 at 12:34 PM

Obvious thing first, have you got the return spring installed?

prawnabie - 28/9/16 at 01:14 PM

Yeah that is in, but it is more of a slinky spring that a return spring!

britishtrident - 28/9/16 at 01:35 PM

Is it the early type (fixed needle) or the later type (floating needle) if the early type you may need to re-centre the jet following the procedure in the manual if later type just slackening slightly the four screws on the dashpot giving it a very gentle tap on the side and very carefully re-tighten using a diagonal tightening pattern 1/2 turn on each screw at at time.

If that doesn't work after a couple of attempts you have either a bent needle or the centre guide is gunged up or you are fitting the dashpot the wrong way round.

britishtrident - 28/9/16 at 01:37 PM

Is it the early type (fixed needle) or the later type (floating needle) if the early type you may need to re-centre the jet following the procedure in the manual if later type just slackening slightly the four screws on the dashpot giving it a very gentle tap on the side and very carefully re-tighten using a diagonal tightening pattern 1/4 turn on each screw at at time.

If that doesn't work after a couple of attempts you have either a bent needle or the centre guide is gunged up or you are fitting the dashpot the wrong way round.

Smoking Frog - 28/9/16 at 03:23 PM

quote:

the diaphragm will turn inside out

quote:

it stops about a mm or 2 away from the bottom of the carb body


Do you have the correct diaphragm?

rusty nuts - 28/9/16 at 05:48 PM

If the piston is sticking with the jet assembly removed have you checked the piston slides freely in the cover with both parts removed from the car? If it's free itmight be worth rotating the cover 90 degrees at a time to see if that helps. If that fails then try a different diaphragm .

prawnabie - 28/9/16 at 07:50 PM

Hi all,

I have had a better look today, the needle is bent, but as above I dont have the jet housing installed so that's not the problem, I also have the dashpot cover on the correct way round, with the lump on the neck facing the air filter.

I have replaced the new diaphragm with the old one - they are exactly the same size, the only difference begin the old one is a bit more "supple" due to age and the piston slides up and down perfectly!! I am going to go with the old diaphragm whilst I research into it a bit more!

Thanks for all the replies!