RobinTR6 Posted June 1, 2007 Report Share Posted June 1, 2007 I have just bought a CP Series car that has been converted to SUs, 1.75 inch with BDM needles.Its drinking fuel at 20mpg and despite fiddleing and reading and fiddleing still not right. The jet on one carb when fully closed (the jet that is) is about a 1/10 of an inch below the bridge whilst the other is level. So have levelled the higher one to the same below level as the other and tried to sync the mixture from there. Still not right. I' am about 3 complete turns down ie rich and car 'burbles' and is a bit lazy and then picks up slowly on max throttle. Synched the air with a meter on boytth at idle so that should be OK. Interestingly exhaust is 'black' on inside of pipes ie rich (car doesnt smoke at all) but plugs are a pinky colour which to me is lean. Tips appreciated. Quote Link to post Share on other sites
marvmul Posted June 1, 2007 Report Share Posted June 1, 2007 Can be a lot of things, ignition and/or carburation. You could take the air filters of and look at the pistons while blipping the engine : they should rise about the same height. When lifting the pistons (engine not running), they should come down again with a click. After removing the covers and pistons with needles, the fuel level is a little lower than the jet orifices (manually work the fuel pump, if no lever on the fuel pump : crank the engine a couple of seconds). Air leaks will greatly disturb the mixture : manifolds, carb spindles, leaks in vacuum line to brake servo or distributor... Quote Link to post Share on other sites
Eyetee Posted June 1, 2007 Report Share Posted June 1, 2007 Rebuilt an SU carb for a 2.5 Daimliar straight 6 and would not get the run right, black exhaust emmissions, replaced the needle, all sweet. Quote Link to post Share on other sites
boxer Posted June 2, 2007 Report Share Posted June 2, 2007 hows the pump pressure to much and it will unseat the needle valves in the float chambers.check out www.mintylamb.co.uk you can compare needles what oil is in the dashpots makes a lot of difference Quote Link to post Share on other sites
Guest ron Posted June 2, 2007 Report Share Posted June 2, 2007 Robin, I've the same set up and the car runs very well and economically on it, it sounds as if some previous owner has been tinkering with the carbs and didn't really know how to set them up, you either need to learn to set up SUs from scratch yourself [not difficult] or take the car to someone who can do it for you. I also think you want to investigate what condition the carbs are in and whether it would be worth while sending them to someone like Burlen for an overhaul, if these carbs have never been overhauled, they are now very old and possibly well worn. It's also pointless having well set up carbs if the ignition system is needing overhauled. Ron Quote Link to post Share on other sites
Bald Rick Posted June 2, 2007 Report Share Posted June 2, 2007 Robin If my memory serves me correct BDM needles should be about right. Assuming float chamber levels are about right then as a rough starting point wind the jets up until they are flush with the bridge. Gently lift the pistons and make sure they drop back down cleanly onto the bridge. Take the jets down EIGHT flats. Then try and start the car. That should be a starting point for adjustment. If you are running with the jets down twelve flats it will likely be far too rich. If you PM me your email address I will scan and send you a leaflet about tuning SU carbs. For SU Carb overhaul I would recommend Andrew Turner. He is easy to find on the net. If you can't find him I'll send his web address to you as well. Hope this helps Tony Quote Link to post Share on other sites
Andrew Smith Posted June 2, 2007 Report Share Posted June 2, 2007 (edited) Robin You might find these sites useful: http://www.teglerizer.com/sucarbs/index.html http://www.teglerizer.com/sucarbs/techtip6.htm http://www.teglerizer.com/suneedledb/index.html Cheers Andrew Edited June 2, 2007 by Andrew Smith Quote Link to post Share on other sites
Andy K Posted June 3, 2007 Report Share Posted June 3, 2007 Robin If my memory serves me correct BDM needles should be about right. Assuming float chamber levels are about right then as a rough starting point wind the jets up until they are flush with the bridge. Gently lift the pistons and make sure they drop back down cleanly onto the bridge. Take the jets down EIGHT flats. Then try and start the car. That should be a starting point for adjustment. If you are running with the jets down twelve flats it will likely be far too rich. If you PM me your email address I will scan and send you a leaflet about tuning SU carbs. For SU Carb overhaul I would recommend Andrew Turner. He is easy to find on the net. If you can't find him I'll send his web address to you as well. Hope this helps Tony Agree, Andrew Turner is your man. Nice bloke, very helpful. Website is http://www.su-carbs.co.uk/ Quote Link to post Share on other sites
RobinTR6 Posted June 4, 2007 Author Report Share Posted June 4, 2007 Agree, Andrew Turner is your man. Nice bloke, very helpful. Website is http://www.su-carbs.co.uk/ Andy, thanks. THE key was getting the jets equal on the bridge as a start as they were quite different when the adjusting hex nuts were fully closed(lean). Having done that then opened the 2 full turns the car was already running better. It was too rich but ran well and have now adjusted back (leaner) and hey presto, problem gone. Given this is a PI car running carbs (ie CP cam etc) any tips on timing and advance etc.... Quote Link to post Share on other sites
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