Bobtaylor Posted April 13, 2019 Report Share Posted April 13, 2019 Hi I have twin CD150 Stombergs on my Vitesse 6. The air valve/needle on the rear carb is sticking, I took the air valve out to examine it and the first thing I found was that the part inside the air valve that retains the needle is lose and moves up and down in the air valve. I checked the front carb and the needle retaining part inside the air valve has no movement at all. On the rear carb it is only the screw that holds the needle that is stopping the whole thing from falling out. Is there anything I can do to fix it? Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 13, 2019 Report Share Posted April 13, 2019 is this the steel insert in the alloy piston base thats moving, regardless of lock screw tightness ???? Pete Link to comment Share on other sites More sharing options...
Bobtaylor Posted April 13, 2019 Author Report Share Posted April 13, 2019 Yes it is the part of the piston that the needle is in. The only screw I can see is the one that fixes the needle, should this also in some way secure the part in the piston? Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 13, 2019 Report Share Posted April 13, 2019 I should know these inside out but cant say ive ever found the needle bush loose in the air valve , If the screw clamps both then it will be fine but if it it a rattling fit relying on the fit of the screw in the piston hole then tho bush needs to be physically fixed Pete Link to comment Share on other sites More sharing options...
Bobtaylor Posted April 15, 2019 Author Report Share Posted April 15, 2019 I have further investigated today, I am talking about the piston which is called an air valve in workshop manual. i took the piston out and removed the grub screw that retains the needle and the whole central tube holding the needle just fell out of the piston. how can I fix it? Link to comment Share on other sites More sharing options...
daverclasper Posted April 16, 2019 Report Share Posted April 16, 2019 (edited) hmm. not sure. Unfortunately JB Weld (liquid metal) 2 part epoxy I have found not resistant to petrol. Don't know if there are others that are?. Also I imagine it would have to be fitted back in centrally, not sure how easy this would be if it's pretty loose. I understand the the pistons are interchangeable between different carbs, so maybe a used replacement?. not sure where from though. I may have a contact no for used carb parts. Let me know if if you want it and I'll try and find it. Dave Edited April 16, 2019 by daverclasper Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 16, 2019 Report Share Posted April 16, 2019 Araldite ??? The steel insert should be fixed make sure whatever you use that the needle screw is clear you dont want the insert fixed and cant fit the screw This seem quite odd I cant say if originally the insert is a light press fit or moulded in the piston Youre about to tell us Pete Link to comment Share on other sites More sharing options...
Bobtaylor Posted April 16, 2019 Author Report Share Posted April 16, 2019 This came to light as I was having problems tuning/balancing the carbs. The first problem I discovered was the jet/needle on the rear carb was sticking as it was not centralised properly. I fixed that and then realised that you could lift the piston (to check the mixture) but the needle stayed put !! There was about 1/8" free movement before the needle moved, I guess that was not helping in making the adjustments. I have ordered a replacement piston as advertised as NOS on eBay, but I believe that not all pistons in 150 carbs are the same weight is that correct? If the is the case would I be better off replacing both pistons with two new ones of the same weight, even if they are not quite the same as the original? I will try to fix the original, but it is quite a loose fit and I am not sure what to use to 'glue' the two bits together, any suggestions? Thanks in anticipation for any advice. Bob Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 16, 2019 Report Share Posted April 16, 2019 the pistons are the same my as far as my experience takes me, only fixed or biased needles are the options you can fit biased needle pistons and needles ( CDSE) into a bottom adjust CD/CDS the weight changes are managed by the thickness of the diaphragm clamp ring Pete Link to comment Share on other sites More sharing options...
daverclasper Posted April 16, 2019 Report Share Posted April 16, 2019 Can you access some digital kitchen scales to compare? 1 Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 16, 2019 Report Share Posted April 16, 2019 if different just swap rings with your originals if the diaphragm is all wrinkled and grown a wash in petrol returns it to as new size the diaphragms have a location lug on the piston and the body make sure these are all located as shown on twiddle day some diaphragms are made of less than supple thick rubber and these make the piston stick ,they should be very thin and flexible like a marigold glove flimsy., some are made from recycled elephant condoms !!!! Pete Link to comment Share on other sites More sharing options...
Bobtaylor Posted April 20, 2019 Author Report Share Posted April 20, 2019 I received my new/replacement piston, all went well until I discovered that the diameter of the tube that retains the needle is at least twice the diameter of the original. So, back to the drawing board, I made a temporary repair by wrapping a small amount of wire around the grub screw to 'fill up' the gap in the side of the piston, this stopped the needle and tube moving up and down and a test drive showed an improvement. I now need to find a way to fix the needle retainer in a permanent way in the piston, or find a correct replacement. Does anyone have an old CD 150 carb and or piston they are willing to sell? Bob Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 20, 2019 Report Share Posted April 20, 2019 Some old fashoined araldite should secure the bush Pete Link to comment Share on other sites More sharing options...
Peter Truman Posted April 20, 2019 Report Share Posted April 20, 2019 Haven't looked at my old spare Stroms, I'm too far away anyway, but if the bush is brass or even steel could you apply/flow some solder onto its outside then rub back a little then drift bush in for a friction fit. I've used this method on other FIX's. Another option do the same as to hold a bearing on a shaft indent the outer surface of the bush so as it increases the outer dia locally where indented. Regards Peter T Link to comment Share on other sites More sharing options...
Bobtaylor Posted April 24, 2019 Author Report Share Posted April 24, 2019 I have made progress, I 'fixed' the needle retainer in the piston with loctite. I don't know if it will last but I have been able to adjust and tune the carbs and it is going like a dream!!!! (at the moment!) Link to comment Share on other sites More sharing options...
daverclasper Posted April 24, 2019 Report Share Posted April 24, 2019 Well done. I think at least, some loctite is petrol resistant. Be interested to know how it goes. Dave Link to comment Share on other sites More sharing options...
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