Jazzman Posted March 20, 2009 Share Posted March 20, 2009 I have noticed the car “jumps” in first and second gear over 2500rpm when accelerating :o. I do not know how to describe the phenomenon precisely: it is like the mix gets messed up and the car jumps until you press the clutch and release slowly while accelerating very gently.I tuned the carbs not long ago and the mix should be right (I colour tuned it) The idling is steady at 750-800rpm and sounds right . The set up is standard for mk3s (SU 1 ¼, with BO needles and original airbox)The only thing I can think of is a problem with the needles of the carbs? :-/ Any ideas?Thanks in advance! Link to comment Share on other sites More sharing options...
Nick Moore Posted March 20, 2009 Share Posted March 20, 2009 If it's doing a kangaroo impression in low gears, it could be the result of a too-light throttle spring. Car goes over a bump, your foot moves on the accelerator, car jumps, foot bounces again and so on. Very amusing to watch but devastating for street cred. Link to comment Share on other sites More sharing options...
GT6 John Posted March 21, 2009 Share Posted March 21, 2009 I think the 'official' term for what your car is doing is 'hunting'. That is if the carbs are the source of the problem.My GT6 was doing it too. I traced the fault to an air leak. Worn throttle spindles. Spray easy start around the carbs and listen for whether the engine note changes slightly. If it does chances are you have an air leak. Link to comment Share on other sites More sharing options...
Clive Posted March 21, 2009 Share Posted March 21, 2009 hunting is normally a sogn of a weak mixture at idle, where the car "hunts" for a steady idle. I don't think this is the case here if it is over 2500rpm. The spring or throttle linkage is a good starting point. And I guess it is the rod linkage, which is a bit more temprimental. Also check the oil in the dashpots, and also, did you have to change the mixture much when you colortuned it? if so it may be partly worn jets and/or needles. Tuning at idle then makes the mixture wrong elsewhere, if that makes sense? Link to comment Share on other sites More sharing options...
Velocita Rosso Posted March 21, 2009 Share Posted March 21, 2009 Cooee, which car are we talking about? Link to comment Share on other sites More sharing options...
Jazzman Posted March 21, 2009 Author Share Posted March 21, 2009 Thanks for your replies,Velocita Rosso, the car is a spit mk3 (1970) with SU HS2 1 1/4 (AUD257) standard carburettors. I rebuilt the carbs last september so it should not be worn parts, apart from the linkage... :-/. I must admit I kept the orignal parts, even though they look worn. What Nick Moore says (Car goes over a bump, your foot moves on the accelerator, car jumps, foot bounces again and so on. ) is exactly one of the symptons! My set up is standard, so I presume the springs should be RED but the paint is gone so IU dont know...I am thinking about buying the following:Needles - new set of standard BO needlesSprings - new set of standard RED springsNew linkage set - I have checked su.co.uk and it seems they do not sell the spitmk3 linkage rod (the kit they offer is for mini and the rod is shorter). Any ideas? Link to comment Share on other sites More sharing options...
Velocita Rosso Posted March 21, 2009 Share Posted March 21, 2009 Steady on .......MK 3 ? is it still wilth rod operated accelerator??If it is, it will cost you ten pence! Link to comment Share on other sites More sharing options...
GT6Craig Posted March 22, 2009 Share Posted March 22, 2009 Hey, this is one of my very symptoms........i seem to have developed everything on this forum!My linkage has a single spring and it has lost its springyness so when i go over even the littest of bumps the car judders forward as the spring goes mental. Basically the spring rate is too low and ill eventually get around to replacing it with a stiffer one.anybody know where to get them? Link to comment Share on other sites More sharing options...
Jazzman Posted March 22, 2009 Author Share Posted March 22, 2009 check www.burlen.co.uk get into their SU branch. Wonderful service and fair prices in general. I will get my things from themPS - Of course I have no relation with them, I am just a happy customer :) Link to comment Share on other sites More sharing options...
GT6Craig Posted March 22, 2009 Share Posted March 22, 2009 Bummer! i have Strombergs, think ill just visit the local engineering suppliers and see what they have - cheers though! Link to comment Share on other sites More sharing options...
Velocita Rosso Posted March 22, 2009 Share Posted March 22, 2009 Thats all it is , the return springs on the carbs have to be able shut off with tension.....weak or worn and the butterflies `flap`Also on the solid linkage (not cable)the linkage to chassis must be strong as wellHence if all above worn then kangaroo jumping occurs Link to comment Share on other sites More sharing options...
GT6 John Posted March 22, 2009 Share Posted March 22, 2009 So this problem should be called 'flappy 'flies' then?! :P ;D Link to comment Share on other sites More sharing options...
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