Replaced coil - now engine idles at 2500 rpm !?
Posted: Sun Jun 19, 2022 12:14 pm
I posted a while back about difficulty with hot start on my 356A , engine is a 1600 Super with Zenith carbs . I thought that the issue was not getting enough throttle opening , as during my brief period of ownership the car seemed to need an open throttle for hot starts . When I checked the throttle linkage I found a lot of slack ( 10mm or almost half inch) in the wire loop at the pivot under front end of gearbox , thought that was the issue.
After a bit of messing around the car would not start at all whether hot or cold and turned out there was no spark at the plugs . I tested the coil and it was open circuit on the secondary , so got a replacement new coil ( Bosch 6 volt from Bosch in Germany ..but made in Brasil ). Fitted it , still no spark . Eventually traced the problem to another open circuit, this time on the 'king' ignition cable connecting coil to distributor . Replace that...bingo ....car starts no problem.
However.....once the engine is warmed up by a 6 mile drive , the tickover revs rise to 2500 , you can drive along without touching the accelerator pedal.
I checked the linkage and made sure the transverse harness rod at the fan shroud was not under tension and there was free play / slack in the wire loop at the pivot under front end of gearbox . The linkage is not under tension , there is some slack in the linkage , and the tickover when hot is still 2500 rpm
I have made no changes or adjustments to the carburettors , not touched the idle adjustment stop screws , not touched any idle mixture settings , not played around with timing or distributor , all that has changed is a new coil and a good connecting lead from coil to distributor .
Before I embark on changing anything I thought I would post here for any useful insight to this mystery .
The simple action would appear to be to screw out the idle adjustment stop screws on each side to drop from 2500 to 1000 and use my trusty SK airflow meter to balance the airflow on each side at idle.....however the SK is designed for air passage diameters between 45 and 55 mm , the Zeniths are at 60mm so waiting a few days for an adapter to arrive by post before I can start !!
After a bit of messing around the car would not start at all whether hot or cold and turned out there was no spark at the plugs . I tested the coil and it was open circuit on the secondary , so got a replacement new coil ( Bosch 6 volt from Bosch in Germany ..but made in Brasil ). Fitted it , still no spark . Eventually traced the problem to another open circuit, this time on the 'king' ignition cable connecting coil to distributor . Replace that...bingo ....car starts no problem.
However.....once the engine is warmed up by a 6 mile drive , the tickover revs rise to 2500 , you can drive along without touching the accelerator pedal.
I checked the linkage and made sure the transverse harness rod at the fan shroud was not under tension and there was free play / slack in the wire loop at the pivot under front end of gearbox . The linkage is not under tension , there is some slack in the linkage , and the tickover when hot is still 2500 rpm
I have made no changes or adjustments to the carburettors , not touched the idle adjustment stop screws , not touched any idle mixture settings , not played around with timing or distributor , all that has changed is a new coil and a good connecting lead from coil to distributor .
Before I embark on changing anything I thought I would post here for any useful insight to this mystery .
The simple action would appear to be to screw out the idle adjustment stop screws on each side to drop from 2500 to 1000 and use my trusty SK airflow meter to balance the airflow on each side at idle.....however the SK is designed for air passage diameters between 45 and 55 mm , the Zeniths are at 60mm so waiting a few days for an adapter to arrive by post before I can start !!