Cold start problem

Suddenly my TD21 has become difficult to start from cold. It cracks up instantly when warm so I presume this indicates that the thermo choke is at fault. I stripped it down and cleaned out a significant amount of crud from the link between the choke and the carb float chamber and the float chamber itself. This made no difference. I also renewed the solenoid for no other reason other than there doesn't appear to be anything else which moves but again this made no difference. I have noticed that when I do manage to start the car and switch the choke off whilst still cold, if I switch the choke back on again it does not start to hiss unless I blip the throttle. This indicates to me that the choke is not working when the starter is turning the motor over and only works once the motor has fired. Anybody any ideas? Posted by Td21 06/11/2015 09:44:26

hi, try looking for a vacuum leak. This may cause the symptoms described.  Good luck Posted by DaveT 06/11/2015 11:36:51

The minute hole in the link piece between no2 carb and the starting carb may have blocked causing no no fuel to get to the latter. Posted by Peter Martin 06/11/2015 12:02:33

Hello Peter & Dave  Many thanks for your suggestions. I have checked the link piece again for blockage but it's squeaky clean and there is no vacuum leak that I can detect. It must be something else but a bit of a mystery at the moment.  Kindest regards  Geoff Widdup Posted by Td21 07/11/2015 16:17:34

Geoff Easy to check if solenoid is working . Car cold everything off , 1 switch on, 2 switch on choke ,you should hear a click as the the solenoid lifts the disc,no click=no choke,could be faulty thermo switch cut out, check by hot wiring the solenoid.  Assuming the solenoid is working ,is the spring loaded choke jet needle free to move downwards?, this happens when you crank the engine over, mine has about 1/4" free travel, no travel =no choke , the handbook tells you how to adjust it ,see also SU Butec data sheets. The probable reason the the choke will not reset with the engine idling is because the induction suction is stronger than the solenoid,blipping the the throttle reduces the suction allowing the solenoid to lift , the hissing suggests the choke system is working but not getting enough petrol into the engine.Finally how fresh is the fuel in the tank?  Good luck Peter Posted by Peter Martin 09/11/2015 15:03:05

Hello Peter  Thank you for this. The solenoid is definitely working and the fuel is fresh. However the needle does not move downward when the engine is cranked over by the starter, only when it fires. I assume that this would point to a suction leak as both yourself and Dave T have mentioned. If I can get the engine to fire it runs fine on the choke. I have fruitlessly checked for leaks and even smeared silicone sealant on every joint but to no avail. I have noticed that the engine is more readily coaxed into life if I pump the throttle whilst spinning the starter which is contrary to published starting instructions. I'll keep fiddling with it. Posted by Td21 11/11/2015 17:25:49

Geoff Certainly sounds like lack of suction,on my car the needle is pulled down as soon as the engine starts to turn on the starter. Grasping at straws, 1,assuming you have the standard air cleaner box  ,how clean are the actual filter elements ,try to start up with the cover plates removed .2 ,Is the ? 3/4" brass connecting pipe from starting carb to inlet manifold  connection piece clear ?.3 ,try pushing the needle down gently as the car is being turned over with the choke on.I assume the actual jet is clear.4 Are there any leaks in the supply pipe to the brake servo, disconnect it and block the hole at the inlet connection with a bolt Peter Posted by Peter Martin 12/11/2015 11:50:23

Geoff Certainly sounds like lack of suction,on my car the needle is pulled down as soon as the engine starts to turn on the starter. Grasping at straws, 1,assuming you have the standard air cleaner box  ,how clean are the actual filter elements ,try to start up with the cover plates removed .2 ,Is the ? 3/4" brass connecting pipe from starting carb to inlet manifold  connection piece clear ?.3 ,try pushing the needle down gently as the car is being turned over with the choke on.I assume the actual jet is clear.4 Are there any leaks in the supply pipe to the brake servo, disconnect it and block the hole at the inlet connection with a bolt Peter Posted by Peter Martin 12/11/2015 11:54:43

Hello Peter  Thanks again for your further useful suggestions but regret still no joy. All jets and passages clear, blocking off the brake servo & taking the air filters out made no difference nor did manually holding the needle down. Very strange. I may have to take it to an SU specialist, I must be missing something. Posted by Td21 15/11/2015 15:00:36

You've gone through the ignition system, proved it all works as it should, tested it? Checked out the coil, the condensor etc when the car is cold? Are the floats in the carbs still floating? It runs perfectly OK when warm, no issues at all that might be indicitive of the problem? Is adequate fuel getting through? When did you last overhaul the fuel pump?   Just some thoughts! Posted by Angus D'Arcy-Drake 16/11/2015 09:49:05