Blesney2000 Posted October 10, 2015 Share Posted October 10, 2015 Hi guys, am new to this forum though not to Club Triumph. Can anyone advise is it possible to put 1500 carbs on my Feb 1968 Spitfire 1300? Are the any issues if so? Quote Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 10, 2015 Share Posted October 10, 2015 you may find the 1500 has HS4 and they wont fit the HS2 manifold or air box if they are the same type/model carb then yes but change the needles Pete Quote Link to comment Share on other sites More sharing options...
Clive Posted October 10, 2015 Share Posted October 10, 2015 Indeed, you can swap the entire inlet manifold and carbs, but probably not a great idea. Unless the HS2's are well past their best and the bigger carbs are really good. Not sure what needles you would need though, but the 1500 ones are unlikely to be ideal (but will work, may be too rich or too lean. Too lean is quite likely.....) Quote Link to comment Share on other sites More sharing options...
Blesney2000 Posted October 10, 2015 Author Share Posted October 10, 2015 Okay then... thanks for the pointers. The carbs in situ are a bit ropey. So what are these other changes I would need to make to efficiently run the 1500 carbs? Quote Link to comment Share on other sites More sharing options...
Nick Jones Posted October 10, 2015 Share Posted October 10, 2015 If your 1300 engine is otherwise standard then in my opinion you'll do better to overhaul the 1.25" SUs you already have. The 1.5" ones are really too big.To put it in perspective, I used to have a tuned 1300 in my Herald with gas-flowed, big-valve head, TH3 cam and 4-2-1 tubular exhaust. This could and did rev to 7000 rpm (or more if I was feeling lucky). I tried a single 1.5" SU on it (on Dolomite log manifold), 2 x 1.25" HS2 SUs (as you have now) and 2 x 1.5" HS4 SUs.Surprisingly enough, the single gave best results to about 4000 rpm, especially lower down. The twins did better at higher rpms, but the 2 x 1.5" only made a detectable difference over 6000 rpm (beyond the red line for a standard engine) and definitely hurt the low down torque and driveability. The 1.25" HS2s were the best compromise and will also be for your engine, which will flow less air than mine did.The SU is a simple beast and straightforward to overhaul with all parts available new. The only non-DIY prospect is if the body is worn where the throttle spindles pass through it leading to air leaks. At that point, getting them professionally overhauled by someone like Andrew Turner is probably your best bet.Nick Quote Link to comment Share on other sites More sharing options...
Blesney2000 Posted October 10, 2015 Author Share Posted October 10, 2015 Done a bit of research and it seems the jets do need to be changed for a leaner size. Just have to work out how to do that now!Thanks again,,, David. Quote Link to comment Share on other sites More sharing options...
Blesney2000 Posted October 10, 2015 Author Share Posted October 10, 2015 Just read your reply Nick. I was hoping to do the switch to the 1.5" carbs cos I can get hold of a pair in better condition than my 1.25" units. Th jet assembly sticks on both of them, one worse than the other. Maybe an overhaul is the answer, I guess the original spec is best.From... David. Quote Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 12, 2015 Share Posted October 12, 2015 Sticking jets after the choke has been operated is down to some simple look and seethe levers and pivots get misaligned with use and some simple lubrication can work wonderssome have found the jet tube is a littleToo long and trim 4mm off its lengthto fit the hs4 you need a replacement manifold and a replacement air filter box Or a new pair of nasty pancakespete Quote Link to comment Share on other sites More sharing options...
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