Colin Fairhurst Posted June 7, 2016 Report Share Posted June 7, 2016 (edited) Apart from issues with linkages and air filters will SU HIF 1.75" carbs. fit the TR3 engine or are there dimension problems. I have carried out various modifications to this engine. At the moment it is running on SU H6 1.75" carbs. I do have a spare later TR4a inlet manifold with the longer runners and I was planning to use this with HS6 carbs then I thought about the possibility of using HIF carbs. Since posting this thread I have thought of another question with the HIF carbs is will they operate satisfactorily when set at an angle as they would be on the TR3 engine? Regards, Colin Edited June 7, 2016 by Colin Fairhurst Quote Link to post Share on other sites
BlueTR3A-5EKT Posted June 7, 2016 Report Share Posted June 7, 2016 I have a pair of HIF's and have toyed with using them on my TR with the 4A inlet manifold. Looks like room enough to fit and you will not have to move the heater adaptor on the RH side/ do some tricky plumbing. A complication I see is that the needle in HIF will be a bias or spring loaded type - Standard SM needles in your carbs use fixed needle so will have to adapt or mess about finding the right needles. Re routing the choke cable will be another requirement and as I recall the H type choke cable is about 2 inches too short for HS carbs. The dash pot spring is a bigger diameter - The right weight of spring will be required - equal to the RED/4ozs as fitted standard. The jets are temperature compensated, It can go go wonky cause rough running. - probably no worse that Strongburps. Give it a try and let us know. Peter W PS PM me and I will scan the relevant pages my 'Tuning S.U. Carburetters' book that covers the HIF in detail. Quote Link to post Share on other sites
peejay4A Posted June 7, 2016 Report Share Posted June 7, 2016 Later HS6s have the biased needles also. Quote Link to post Share on other sites
Colin Fairhurst Posted June 7, 2016 Author Report Share Posted June 7, 2016 I have a pair of HIF's and have toyed with using them on my TR with the 4A inlet manifold. Looks like room enough to fit and you will not have to move the heater adaptor on the RH side/ do some tricky plumbing. A complication I see is that the needle in HIF will be a bias or spring loaded type - Standard SM needles in your carbs use fixed needle so will have to adapt or mess about finding the right needles. Re routing the choke cable will be another requirement and as I recall the H type choke cable is about 2 inches too short for HS carbs. The dash pot spring is a bigger diameter - The right weight of spring will be required - equal to the RED/4ozs as fitted standard. The jets are temperature compensated, It can go go wonky cause rough running. - probably no worse that Strongburps. Give it a try and let us know. Peter W PS PM me and I will scan the relevant pages my 'Tuning S.U. Carburetters' book that covers the HIF in detail. Thanks for that. My old TriumphTune catalogue suggests BAB standard, BAE slightly rich and BAM for PlusKit B for the TRs using the later HS6 carbs with biased needles with springs.I was thinking that the same would apply to the HIF carbs. I am running on RH fixed needles in the H6 carbs at the moment which are quite rich. The red coloured 2.5 inch diam. dash pot springs listed are 4.5 ozs and are the lightest weight in that range. Regarding the temperature compensation in the jets, I have in the past replaced the wax capsule with a one P coin on the 1.5 inch SUs and then readjusted the jets. Maybe it is possible to do something similar with the HIFs. Regards, Colin Quote Link to post Share on other sites
peter clarke Posted June 8, 2016 Report Share Posted June 8, 2016 You can buy a conversion piece to change from bias to fixed needles. Quote Link to post Share on other sites
peejay4A Posted June 8, 2016 Report Share Posted June 8, 2016 How do you go about centring the needles if you've converted? Isn't the jet block different? Quote Link to post Share on other sites
Lebro Posted June 9, 2016 Report Share Posted June 9, 2016 No. It, s the same. Bob Quote Link to post Share on other sites
peejay4A Posted June 9, 2016 Report Share Posted June 9, 2016 Thanks Bob. Something else I didn't know. Quote Link to post Share on other sites
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