This engine has a modified Jaguar (Lucas I believe) point ignition system which because of modifications, I am finding impossible to maintain. It has been running but because of deteriorated spark wires necessitated my replacing the plug wires. It has a modified rotor (with additional spark contact inside 180 degrees with the original contact. I has a modified cap with a carbon contact in place of a vent location on the top as it has a boss for this and another on the side where a second coil HT wire sits with another coil wire sitting on the center. There are two points sitting on a mounting plate; each goes to a separate coil. The modified rotor and cap show contact deterioration (arcing), points and need to be replaced but I am faced with modifying stock parts.
I am also considering going back to original ignition to simplify future maintainance, so I am putting up this query as how to proceed with this. Used ignitions are available in SoCal. Lucas or Marelli? What parts off donors should I obtain. Should I upgrade to Pertronix or Lumenition or other aftermarket electronic ignition? Any comments are appreciated. Thanks
It has been converted to Webers sources from Fiat 124; these have equal barrels and are all mechanically linked. The current distributor does not use the vacuum (is present but no vacuum connected).
What a lovely car Eduardo and a very cool setup with the Webers…!!
Must be a blast to drive.
I had a Fiat 124 Coupe (that I loved) with a double barrel Weber, a very decent carburettor and easy to maintain.
That Distributor cap sure is bizarre, don’t understand what they where trying to achieve, and that second carbon contact must wear pretty fast.
I would go with the Lucas CEI, simpler than the Marelli and easier to find.
You will need the distributor, the ignition amplifier (has a GM module inside) and the upgraded single coil (or two normal coils in parallel)
The Marelli, albeit being a more advanced system, has a bad habit of loosing one bank, you don’t notice it right away, the oil get’s washed from cylinders with gas and the fuel combusts at the Cats melting them. Not a Marelli expert though and I don’t know what you will be needing.
Also, download the JXS Help book from this site, lots of pertinent info.
And I think you should connect that vacuum advance.
That’s an interesting beast! I second the suggestion of Lucas CEI as per Wiggles. You do seem to have options, either source secondhand for 40 year old electronics or get a new ReOpus; don’t know the cost of a junkyard kit, or offhand when the original Opus changed over to CEI. I’m sure that is on the forum here someplace.
After further investigation, while vacuum bellows still on and connected, the mounting plate for the points do not rotate and are fixed so that only centrifugal advance is functional ( the rotor shaft moves). The carbs appear to have a couple of plugged ports just above the throttle plates probably suitable for a ported vacuum source. Couldn’t find any ports on the short runners under the carbs.
So based on the modified rotor, distributor cap, unknown points, locked mounting plate for the points, it is going to take some effort and time to get this figured out and replaced. After figuring out the costs for new parts, a replacement is indicated.
I am looking into Terry’s Jag set up as Wiggles mentioned to verify fit etc. Will keep progress posted here.
The first time I saw a Jag V12 in a hot rod (a 30s or 40s something) was at a car show in Milwaukee in the 60s/70s.
The engine bay was open which really showed off the engine and the guy had fashioned 12 individual exhaust pipes that swooped out of either side of the engine bay to form the running boards. Chromed of course. They ended just forward of the rear tires - which were ginormous.
Not a muffler to be seen - I would have loved to hear it run but the show was indoors.
I have ended up purchasing the replacement kit from Barratt for carbureted engines. Just about ready to install it. Pulled the spark plugs and all were heavily sooty and a couple of the piston tops seemed oily. I am reserving judgement but believe that the ignition system was not functioning well. I cleaned them off and the spark plug wells prior toe their removal. No electrode wear on the NFK TR5 plugs (are these hot enough?). Harbor Freight plug cleaner and wire brush used to clean the carbon deposits. Could the lack of vacuum advance or retard have caused the carbon deposition?
I am also considering that the Weber 28/30 DHTA 5/279 carbs (from Fiat Stradas) are too rich and not jetted correctly but I will wait to solve this once a proper ignition is operational.
I am also trying to locate a suitable vacuum port on one carb to connect to the new distributor. Was able to locate carb jetting and diagrams online at Classic Carbs (UK) .
Getting more familiar with the difficulties fining my way around the engine but have found techniques and tools to help me service the ignition system.
Good adherence to the rule of fundamentals: however, unless someone had a rolling road, or was very familiar with how to set those carburetors up on the car, it’s highly likely that they are not jetted properly.
The Weber carbs were stripped of all accessories and unneeded ports are plugged. The original carbs on the Fiat engine fed 375 cc per barrel and the current 5300 cc Jaguar works out to 442 cc’s per barrel. I am assuming the the jetting was modified to account for this larger displacement. I will finish correcting the poor ignition and lack of vacuum-modified timing and see where that leads.
I will have to say that the exhaust on the Jag does not reek of gasoline unlike other hot rods I have had contact with that were obviously excessively rich.
I installed the Barratt kit (including the complete distributor, amplifier unit, resistor pack and coil. Mounted the pack and coil at the right front head and the amplifier unit on an aluminum plate in the front of the engine valley. Cleaned the plugs and reinstalled them. Put labels on the dist cap ports and am getting ready to plug the cables in. Made a small wire harness from the resistor pack with tach, ignition wire and start ignition wire) which has been fished to the underdash area for connections.
I was able to locate a port on one of the Webers for the vacuum port connection but wonder if the vacuum from just one carb venturi will result in erratic vacuum levels. I am wondering if getting vacuum taps from two other carbs will help even out vacuum pulses.
Also am considering using a vacuum reservoir to even out the vacuum pulses to the distributor vacuum advance. Did the carbureted V12s use a vacuum reservoir and did they use a vacuum tap from one carb only or from a manifold with more than one venturi.
Would appreciate comments from other v12 users. Thanks.
AFAIK, none of the carbureted V-12’s used vacuum advance distributors, instead they had a vacuum retard distributor that made the engine run inefficiently and heat up fast so it spent less time warming up. When the water reached a certain temperature the thermoswitch would disconnect the vacuum from the retard module. Later FI cars had a vacuum advance module, which required ported vacuum, which is zero at idle, maximum at cruise throttle opening and zero at full throttle. Vacuum advance is only active when cruising at a constant speed, and then the only effect is to reduce fuel consumption when at partial throttle. You could live very well without it, especially on a hot rod.
