Iain T Posted June 23, 2022 Report Share Posted June 23, 2022 My front carb before and after rebuild leaks dashpot oil. As a CDS it doesn't have the needle top adjuster and seal. The oil tube in the air piston is a blind hole so in theory can't drain down. Where is it escaping from? The rear carb seems OK it's only the front that leaks. FYI when I push the dampers in the front requires slightly less force. The same as when I manually raise the air pistons with the damper in place, the front is slightly easier. Could it be a micro crack in the air piston? I think the only way to test it is to remove the piston clean it and fill with oil and see if any seaps out? As to the differing forces is this just different clearances between the tubes and dampers. I tried changing the dampers over and get the same result so it does point to the front air piston being the problem. No I don't overfill!! Advice please. Iain PS jets are centred and air piston drops to the bridge with a clunck or it could be a clonk.... Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 23, 2022 Report Share Posted June 23, 2022 how about the dash tube diameter is different ?? there are other dashpot dampers about . does it leak when left or is it pulling oil over the top when the piston drops rapidly ?? does ot drop to empty or find its own operating level ?? Pete Link to comment Share on other sites More sharing options...
Iain T Posted June 23, 2022 Author Report Share Posted June 23, 2022 The heatshield is always oily but I haven't cleaned the shield filled the air piston and left it without running the engine. I think when Carburettor Exchange refurbed the carbs they fitted new dampers. They look new. I spoke to them and they can supply another air piston to try. The front carb oil drops so that there is very little damping effect compared to the rear. I'll measure the diameter of both dampers and report back. Iain Link to comment Share on other sites More sharing options...
Iain T Posted June 23, 2022 Author Report Share Posted June 23, 2022 Just checked the damper diameters, both 366 to 367 thou taken at various places. I can't see much wrong there. I 'filled' to below the register line yesterday and apart from starting up to move it back a few yards this morning the engine has not been run. The heat shield was clean yesterday but oil on it now. It must be coming from a porous or micro crack in the air piston? The rear carb shield is dry. Iain Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 23, 2022 Report Share Posted June 23, 2022 ok how is oil getting from inside the carb throat thats leaked out of the dashpot and end up outside on the heat shield to me thats more fuel related to seapage from the jet adjuster and if the dashpot is seaping it can exit via the jet 0 rings but its unusual and more likely you are seeing fuel residue do a finger wipe does it smell ??? Pete Link to comment Share on other sites More sharing options...
Iain T Posted June 23, 2022 Author Report Share Posted June 23, 2022 I've done the finger wipe and it's oil. Coffee time now then I'm going to take the dash pots off. The guy from Carburettor Exchange couldn't understand it either. If it was a 175 or later 150 with the top needle adjuster I could understand it but not a CDS with a blind hole... Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 23, 2022 Report Share Posted June 23, 2022 so its fill em up and hang it up overnight see what coming from where ?? we await a result any leak or overspill will leave the piston via the two holes in its base but to exit oil from the jet holder has to be a duff 0 ring on the jet tube it should be contained within the carb Pete Link to comment Share on other sites More sharing options...
Iain T Posted June 23, 2022 Author Report Share Posted June 23, 2022 Took front dash pot off, can't see any sign of oil stains on the air piston but it is oily. I noticed you only have to put a very small amount of oil in to dampen and I may have been putting too much in!? I only normally fill to the lower line but that's at the top of the air piston damper tube so with the damper in place and the air piston moving up oil would have been coming out and dribbling down to the bridge? Any how screwing the dash pot back on I couldn't get the air piston to drop properly so I wound the jet up and recentred the jet. Then as I had time I recentred the rear carb jet and set both jet depths the same as before I tinkered. I then put a small amount of oil in both dash pots and cleaned everything. Both air pistons felt about the same when lifted. I agree for anything to come out the jet assembly O ring is letting it pass. I do remember the jet assembly bore in one of the carb bodies was as rough as a bears a*s*. I think this may be why oil or petrol is coming out the bottom. Engine started up very nicely with stable tickover. I'll take a look tomorrow and probably take it for a spin. Link to comment Share on other sites More sharing options...
Iain T Posted June 27, 2022 Author Report Share Posted June 27, 2022 I waited until I took the car for a good fast drive until reporting back. No oil dribble before Sunday's drive to the car show at Rochford and none now! Conclusion I must have been overfilling the dash pot and due to an iffy jet body seal oil was coming out the bottom onto the heat shield? It all works so another lesson learnt, only fill until you can just see oil and feel resistance in the damper. Iain Link to comment Share on other sites More sharing options...
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