2009poolesparky Posted December 24, 2015 Share Posted December 24, 2015 I've noticed the springs inside my hs2 carbs have been stretched and this makes it harder for the piston to rise slightly. Will this have a big effect on running and accelerating? What would have originally been fitted if I need to replace them? Thanks Quote Link to comment Share on other sites More sharing options...
piman Posted December 24, 2015 Share Posted December 24, 2015 Hello Poole sparky, yes the springs have an effect on the running, increasing the tension will tend to weaken the mixture. If you reply with what car and it's year that you have then I can tell you what spring you should have?Alec Quote Link to comment Share on other sites More sharing options...
2009poolesparky Posted December 24, 2015 Author Share Posted December 24, 2015 Ok thanks, that might be the cause of my sluggish and gutless road tests. It's a mk2 spitfire 1147cc 1966 Quote Link to comment Share on other sites More sharing options...
piman Posted December 24, 2015 Share Posted December 24, 2015 Hello Poolesparky, my Burlen book doesn't list an 1147 Spitfire, however the Spitfire MK 1 to Spitfire MK 1V all use the same spring, AUC 4387 red marking on the top spring coil. (Although the colour has probably long gone)Alec Quote Link to comment Share on other sites More sharing options...
Clive Posted December 25, 2015 Share Posted December 25, 2015 Are you sure they are stretched? I ask as they are quite long compared to in the carb, and I have never seen a damaged one. I have checked springs to see which ones I have fitted on "unknown" carbs. I used digital kitchen scales and a ruler....compress the springs bu an inch and see how the "weight" changes. Also I am trying to get my head around the effect of stretching. I think it may richen the mixture.SU's are very clever, and not always what you expect. There are 2 things that affect mixture. One is the needles/jet, thinner the section of needle more fuel can pass. So higher the piston.needle the richer the mixture.However, the lower the piston the faster air travels over the jet. This sucks more fuel. This is the reason putting thicker oil in the piston damper means you get more and longer enrichment during acceleration (lots of people think thin oil gives more enrichment as the piston rises faster-wrong!)Which one of the above has the bigger effect? well, it has to be a mixture of the 2. Lacklustre acceleration may be down to thin oil in the damper...or just poor setup. I can get a car to run OK, but I know a couple of people who are magicians with SU's. That is what you may need. Quote Link to comment Share on other sites More sharing options...
piman Posted December 26, 2015 Share Posted December 26, 2015 Helo Poolesparky/Clive, I think it's worth looking at the engine as a whole, not just focussing on the carburettors, a lot of people are set on going by the book when timing the engine but that doesn't necessarily give the best result so the carburettors get blamed as the 'timing is spot on'.Alec Quote Link to comment Share on other sites More sharing options...
2009poolesparky Posted December 26, 2015 Author Share Posted December 26, 2015 Yes I was just asking as I'm running out of ideas what it could be now. I have been working on the car, replacing and fixing lots of parts, including overhauling the carbs, they have new jets and AN needles now, new spindles too. The vacuum advance was broken so that was fixed and the weights in the dizzy were free too. I have set the mixture correctly also and the timing is set to 13° btdc. The car seems to idle nicely and rev up well too, but when driving it just feels gutless Quote Link to comment Share on other sites More sharing options...
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