BillMain Posted November 14, 2004 Report Share Posted November 14, 2004 Hi, I've got a 1968 build TR6 ex Californian which was returned to the UK in 1991 and had a ground up restoration in 1997. The engine number is CC/25884-HE which is the original one when shipped to the US. It is now fitted with HS6 carbs but the distributor has both vaccum retard and advance which I've been told is incorrect and it should only have the vaccum retard. From the wealth of information out there can anyone help shed some light on this for me and advise of the correct one? Quote Link to post Share on other sites
saffrontr Posted November 14, 2004 Report Share Posted November 14, 2004 Hi Bill, When originally built the 1968/69 US spec TR6 were fitted with both the vaccum retard and vacuum advance capsules on the distributor. It was only from engine no CC58298 that they became retard only distributors. The advance capsule fed directly to the front carb and the retard capsule to the vacuum control assembly and thence to the rear carb. There was also a rigid vacuum balance pipe between the two carbs. The Roadster Factory parts book has a very good diagram that I could scan and email to you and I also have a factory photo of the engine bay of CC27025LO which also shows the arrangement. Send me an email if you want copies. Regards Derek saffrontr@tiscali.co.uk Quote Link to post Share on other sites
BillMain Posted November 15, 2004 Author Report Share Posted November 15, 2004 Hi Derek, If you could send the information that would be great. My e mail address is Bill.Main@ecosse.net Cheers Quote Link to post Share on other sites
foster461 Posted November 19, 2004 Report Share Posted November 19, 2004 I've put my boy into storage for the winter so I'm turning to some of the many small restoration projects to get ready for the spring. One of them is to build a new distributor. My plan is to start with the early dizzy with both advance and retard, remove the retard because that is just an idle emissions mechanism as far as I know and just retain the vacuum advance to provide better performance. I bought an old MGB unit on ebay that I will canibalize for parts like the spring and vernier style nut to replace the retard unit. I think this will look better and perform better on this 1974 and a half car. Stan Quote Link to post Share on other sites
Tom Fremont Posted November 19, 2004 Report Share Posted November 19, 2004 The vacuum retard function requires a working valve in the carburetor linkage to operate per original. It was designed to retard the timing only when at idle, to 8 degrees ATDC, which results in a drop of ~ 400 rpm and a very smooth purr of an idle with lower emissions - the purpose to begin with. Once off idle, the retard function is totally disabled and the vacuum advance takes over. The vacuum for the retard function was supplied from a branch in the same rigid tubing which supplied the throttle bypass valves on the Stromberg emissions carburetors, all from a double banjo fitting on the brake booster nipple. For the advance, it was per Saffron TRs post. Very few examples seem to have this feature operational, as knowledge of its workings is rare, the vacuum switch/valve is no longer available and it isn't an essential function anyway - the port on the manifold fitting which feeds vacuum to the switch can be blanked off and the idle speed adjusted to suit. When I ran the stock engine in my TR250 I loved this feature and went to some pains and expense to keep it going. With the S.U. conversion you probably don't have the vacuum circuit now anyway..... Quote Link to post Share on other sites
jean Posted November 19, 2004 Report Share Posted November 19, 2004 Very interesting Tom. I have seen quite some folks struggeling with this layout on their imported U.S. cars, but never understood how the buggers functioned. Half of the gadgets on these cars were probably missing. See... you never stop learning jean Quote Link to post Share on other sites
foster461 Posted November 22, 2004 Report Share Posted November 22, 2004 It was designed to retard the timing only when at idle, to 8 degrees ATDC, which results in a drop of ~ 400 rpm and a very smooth purr of an idle with lower emissions - the purpose to begin with. So here's a question - is an engine whose idle rate is slowed due to retarded ignition going to idle better than the same engine whose idle is set via the throttle ?. I had planned to remove the retard because I thought it was adding no value (emission control at idle) and because I wanted to eliminate another potential source of vacuum leaks. If it turns out that the retard is a benefit I would reconsider.. Stan Quote Link to post Share on other sites
Tom Fremont Posted November 22, 2004 Report Share Posted November 22, 2004 an engine whose idle rate is slowed due to retarded ignition going to idle better than the same engine whose idle is set via the throttle ...that was always my experience over 18 years with it. Relatively speaking, however, the cam in the carb cars will always produce a smoother idle than a 150 BHP cam with or without the vacuum retard. So it's really a question of whether you want smooth or smoooooth. If you want the experience of 100% authenticity from 35 years ago you'll have to do it! Guaranteed to bring a smile once done.... :: Quote Link to post Share on other sites
Tom Fremont Posted November 23, 2004 Report Share Posted November 23, 2004 8 degrees ATDC ...I believe that should be 4 degrees ATDC. To experiment, you could screw in the idle screws until about 1200-1400 rpm, then pull the right-hand vacuum pod rightwards as if to adjust the timing ( by 2 degree increments, by turning the pod 1/2 a turn at a time ). The amount of movement required just to disengage the dual tongues of the pod, without turning it, will approximate the effect of the retard function. See how you like the idle at that point :: Quote Link to post Share on other sites
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