5 replies to this topic

[Coalhod]

Hello;

 

I'm in the States or else I would book a session with AC Dodd to rectify the above problem.

 

Ignition is a Pertronix II module on a rebuilt 25D distributor with their recommended 0.6 ohm coil.  Carburetion is 2 X HS4 SU's using MME needles and red springs, 20w-50 synthetic oil in the dashpots.

 

AFR gauge installed with oxygen sensor mounted on an LCB manifold just downstream of the exhaust collector with an RC-40 2 box system.

 

At idle I'm reading 12.5-13 AFR and climbs to 14.5-15 AFR on acceleration.  Car pulls like a train.  On deceleration and at low rpm or when coming to a stop the AFR goes to 16-17 almost off scale and the engine wants to stall.

 

I'm thinking ignition problem and may have to go back to contact breaker points and that may be the way to tell if any change happens with the way the car is running.

 

The lean condition on deceleration has me puzzled all I can reckon is that as the car decelerates it causes higher vacuum and the dashpots are being lifted too quickly causing it to go lean.  Maybe go to a heavier yellow spring?

[Chris1275gt]

https://www.google.c...=DppcPFFjEpEQVM


https://www.google.c...=rjl7jHgnA_qvaM

Edited by Chris1275gt, 23 October 2023 - 04:17 PM.

[Coalhod]

FWIW I did a wholesale change and removed all of the Pertronix items and went back to contact breaker points with corresponding Bosch 3.0 ohm "Blue" coil.  All of the above running symptoms have disappeared.  It does not rev to 6500 rpm quite as freely, however I may experiment with a 23D Cooper S baseplate and 32 oz. points over the winter.  Still pulls like a train.  My only concern is the AFR is around 11.0 at idle.

[ACDodd]

11.0 at idle is borewashing. Idle mix needs to
Be adjusted to 13.5 to 13.8:1. If it leans out when driving the needle profile is incorrect. Mixture screws MUST NEVER be adjusted to achieve correctly part throttle running.

The reason the mix was leaning out with the high power
Ignition system is that the spark energy was sufficent tomburn all the fuel during over run, something which the standard pints ignition is unable to do. Lean running on overrun is what you want to achive.

I offer video tuning for people who are international.

Ac

Edited by ACDodd, 24 October 2023 - 07:57 PM.

[Earwax]

Hi  Coalhod     I will just mention for your consideration .....  

 

If your cam is a bit lumpy ( say equiv of 286) then sometimes the idle revs need adjusting up.to avoid stalling situations like clutching in when the traffic light turns red. -  

 

Secondly - do you know what your ignition curve is and your Petrol MON/RON . I think you have access to good petrol/gas .... which may allow advancing the ignition curve early on ..... obviously changes here may need a further adjust of fuel.   I am an advocate of mapping your distributor to suit your specific setting.. and I don't assume the curve is as stated on the new dizzy

[Coalhod]

Many thanks for the suggestions!  I need to get to a rolling road to do further testing/modifying of the engine.