pfenlon Posted April 24, 2009 Report Share Posted April 24, 2009 I have only just noticed that my 250 engine that I have begun to hopefully unseize has to me, a new type of distributor. Having 2 vacuum units, why is this please, emission stuff? Is it junk ?, for the UK do I need a standard one? as usual all info gratefully recieved, Peter Quote Link to post Share on other sites
Chris Mountford Posted April 24, 2009 Report Share Posted April 24, 2009 Hi Peter, My understanding is that they have a vacuum advance AND a vacuum retard. All this I reckon to improve the emissions. As for whether you need it in the UK depends upon whether you are going for performance or originality. If performance is the thing the old way would be to source the TR5 or early TR6 distributor part number 41219B which has no vacuum advance at all, but relies on the mechanical advance generated by the 'bob' weights. Cooper 'S' distributors worked on the same principle. I suppose nowadays that an electronic device will improve on performance and economy Choice seems to be with you regarding what you want it to be when its done. Chris Quote Link to post Share on other sites
johnny250 Posted April 25, 2009 Report Share Posted April 25, 2009 I have only just noticed that my 250 engine that I have begun to hopefully unseize has to me, a new type of distributor. Having 2 vacuum units, why is this please, emission stuff? Is it junk ?, for the UK do I need a standard one? as usual all info gratefully recieved, Peter Yes Pete, the 250 has vacuum advance and retard capsules for emission regs ......I cut off the retard one and left the stub as a manual 'knob' to twiddle.... worked OK, but as i'd tweaked engine and all, and the distributor cam/springs/etc wouldn't match, decided on fitting the Megajolt ignition system instead....no dizzy required. john Quote Link to post Share on other sites
heliguy Posted April 27, 2009 Report Share Posted April 27, 2009 Yes, the TR250 had the "push me pull you" advance on it. If you are going to take it off, im sure some TR250 guys in the States would be happy to purchase it from you. As has been mentioned, it was an emissons thing to have a retard on it, so it really is redundant if you are going for performance.... cheers, Mitch Quote Link to post Share on other sites
Tom Fremont Posted April 28, 2009 Report Share Posted April 28, 2009 The '250 distributor's retard capsule was actuated only at idle, switching off and over to advance once the throttles commenced to open. The significant points about these are the 13 degree bob weights ( which give 26 degrees of crank advance ) and the springs used therewith. Some were supplied with 10 degree weights according to the Bentley bible. Both can be changed to give whatever behaviour you wish. Obviously the vacuum capsules can be disconnected. Apparently fast road engines prefer less advance than clean burners . I got 7 degree dizzies for mine and set them to ~ 12 degrees static, thus maxing out at 26 degrees. Note that the vacuum advance assist on the '250 dizzy will result in over 40 degrees of advance in conjunction with the mechanical advance. Even when I ran a stock '250 engine I found it preferred to go without the vacuum advance, and the static setting was about 10 degrees BTDC. This was reduced to 6 degrees when used on a CP spec engine on Webers later. Though probably of academic interest only, the vacuum retard feature on the stock engine ( 10/50/50/10 cam ) gave an inimitably smooth idle besides getting it under the emissions wire. I much enjoyed that purr and worked assiduously to maintain its operation, once spending a fortune for the little plastic vacuum valve which opens the retard circuit at idle. I can't recall ever seeing another example with this operational in the 33 years I've owned a '250. I have retained the full apparatus in the event someone someday may want to convert back to original. Quote Link to post Share on other sites
foster461 Posted April 28, 2009 Report Share Posted April 28, 2009 The '250 distributor's retard capsule was actuated only at idle, switching off and over to advance once the throttles commenced to open. The significant points about these are the 13 degree bob weights ( which give 26 degrees of crank advance ) and the springs used therewith. Some were supplied with 10 degree weights according to the Bentley bible. Both can be changed to give whatever behaviour you wish. Obviously the vacuum capsules can be disconnected. Apparently fast road engines prefer less advance than clean burners . I got 7 degree dizzies for mine and set them to ~ 12 degrees static, thus maxing out at 26 degrees. Note that the vacuum advance assist on the '250 dizzy will result in over 40 degrees of advance in conjunction with the mechanical advance. Even when I ran a stock '250 engine I found it preferred to go without the vacuum advance, and the static setting was about 10 degrees BTDC. This was reduced to 6 degrees when used on a CP spec engine on Webers later. Though probably of academic interest only, the vacuum retard feature on the stock engine ( 10/50/50/10 cam ) gave an inimitably smooth idle besides getting it under the emissions wire. I much enjoyed that purr and worked assiduously to maintain its operation, once spending a fortune for the little plastic vacuum valve which opens the retard circuit at idle. I can't recall ever seeing another example with this operational in the 33 years I've owned a '250. I have retained the full apparatus in the event someone someday may want to convert back to original. Tom, just to be clear, your current config with the webers/cam/head is 6 degrees btdc static timing ? Quote Link to post Share on other sites
Tom Fremont Posted April 28, 2009 Report Share Posted April 28, 2009 Tom, just to be clear, your current config with the webers/cam/head is 6 degrees btdc static timing ? No, that was before the 1st 7 degree dizzy, set to ~ 12 deg BTDC. These are getting rare in original form, and I'm lucky to have gotten (2) such with vernier adjustment I attribute this to careful handling of my suppliers Quote Link to post Share on other sites
pfenlon Posted April 29, 2009 Author Report Share Posted April 29, 2009 Brilliant thanks chaps a mine of info, but after the electronic ignition I fitted to my TR3A lasting 10 miles or so, I dont have a lot of confidence in it, but I must be wrong everyone and his dog use it apparently. thanks again for your help Pete Quote Link to post Share on other sites
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