| Author | Message | ||
     Christian S. Hansen Grand Master Username: enquiring_mind Post Number: 862 Registered: 4-2015 |
1955 Silver Dawn SUJ 128 Late in the series RR used twin SU carbs on the Silver Dawn which previously had only a single Zenith(?). Can anyone tell from these photos the model of SU carb? Are they the same as supplied with the Bentley R Type, or the same as what was put onto the Silver Cloud the next year in 1956? I want to balance the mixture settings and presume that Kelly Opfar's dial tools are the "go to" choice for this operation. As it is, the mixture seems overly rich and grey smokey at fast idle when engine is cold started in morning and stays that way for longer than I suspect is necessary until the fast idle choke setting finally kicks off. On these carbs the mixture jet is adjusted with a hex end at the bottom which is itself covered by a hex cap. The manual directs that the two carbs be adjusted and balanced "by ear" which I suppose is fine if you have been trained and experienced in the procedure but I can only pretend to have that level of experience and instead have basically no idea what I am doing! Am I correct to assume that Kelly's dial tools will assist? I presume that they assist by matching the height that the piston is within the carb pot or does that have nothing to do with balancing the idle mixture settings? All advice is solicited and gratefully accepted.    . | ||
| Mark Taxis Prolific User Username: mark_taxis Post Number: 158 Registered: 4-2007 |
The carbs are H6. Kelly's measuring instrument will tell you if the carbs are balanced, it will not determine if the mixture is correct. However you need to ensure that the carbs are balanced before you fiddle with the mixture. I intend to buy one of his masterpieces at some time in the future, in the meantime I use a plastic drinking straw. With the engine running at idle remove the oil damper rod and insert the straw, mark the straw with a felt tip pen where it is level with the top of the carb. Now move the straw to the other carb and it should be at the same level, if not adjust the throttle until the same. as a double check I also do this with the engine running at fast idle. | ||
| christopher carnley Unregistered guest Posted From: 86.138.60.58 |
They are a special type of H6 with an automatic choke. Balancing them is tricky which ever method used. There is information in BB 157 through BB 208 (Message approved by david_gore) | ||
| Christian S. Hansen Grand Master Username: enquiring_mind Post Number: 863 Registered: 4-2015 |
Christopher... Thanks for the reference to the Bulletins. It certainly was serendipity that I acquired the set compiled and published by RR in 1972. It is however a mystery how they are organized. They do not seem to be sequential by either number or issue date. I did find BB157 (1952) 188 and 188A (1954) and 208 and 211 (1955) which seem to apply to this later auto choke system. I will study them before doing anything further. My feeling is that the choke mechanism stays on too long and that for the duration that is why the exhaust is so smokey. I will hope that there is procedure for it dropping off sooner and at a lower temperature. Mark... Thanks for the information. Upon reflection I can see that the piston height affects the air flow but not the mixture of that air flow. I therefore have several adjustments to study. On one hand, balancing the air flow and mixture when at operating temperature and on the other, the starting choke and fast idle settings. . |
