V12 Hot coil problem & leaky carburettor

[Lemans88]

'73 FHC owned for 30+ years - starts & runs well BUT after 3 or 4 miles under load misfires commence leading to total engine cut out, with v hot coil.

After cooled down, situation returns to normal, then repeat of problem.

I have changed the coil. No difference.
Not being electrically wise, & assuming that both coils cannot be at fault, is this a ballast resistor fault with too many volts going through the coil after start up?

AND one carburettor has developed a leaky O ring at the base of the jet tube. The works & parts manual indicate that this is a threaded "screw-in from below" part of the float chamber, but all of the carbs on my vehicle seems to have the item pressed in. Does this mean a complete carb. rebuild simply to replace the O ring?

Any help on either of the above would be MUCH appreciated.

Thanks in advance.

[Whitact]

The misfire sounds like the original OPUS unit is failing which is very common. A replacement system such as the one from SNGB may well cure it.
The O ring replacement procedure is probably in the Stromberg rebuild info in the Knowledge base.
Cheers

[vee12eman]

Hi,

As you say, there are O rings below the jets. Earlier versions of the carburettors had mixture adjustment nuts located here, but carbs fitted to the V12 E-type have mixture adjustment incorporated in the dashpot controlled piston, which moves the needle, not the jet. Rather than redesigning the reservoir and filling in the hole, a plastic plug was fitted, with an O-ring to seal and an external brass cap, which can be seen from below the carb. The plugs clip into position and retain the plug securely only if the moulded in clips are in good condition.

Given the age of the carburettors, the environment in which they operate and the constant dousing in fuel, several issues have arisen within this set up:

1. The fuel and heat have hardened the plastic of the clips so they often fail when removing the plug, or even when re-fitting. Sometimes they even fail in situ with no apparent reason.

2. The O rings will have hardened in the same way and eventually lose the ability to seal and to reform if removed and refitted.

3. The sealing face around the O ring, i.e. the inner metal face of the hole in which the plug is located, may have corroded and reduced the quality of the seal, typically, a new seal may not be able to cope with the pitting this has created, so new seals sometimes do not do the job.

To overcome these issues, its best to replace the entire plug and seal assembly. Whilst it is removed, clean the inner sealing face of the hole and check for corrosion, if any is found either replace the reservoir (the base of the carburettor) or, if the corrosion is not severe, use a very small amount of fuel resistant sealant around the plug seal, taking care to ensure that this does not end up inside the carburettor reservoir, where it might migrate and cause problems elsewhere. Personally, I would use the sealant even on new reservoirs with new plugs and seals, but again, I stress the need to keep the sealant out of the reservoir.

As this probably requires removal of the carb to inspect, clean and possibly replace the reservoir, then it is probably wise to address replacement of the very small seals around the adjustment nuts in the base of the dashpot. You can access these easily without carb removal, but it necessitates tuning the carbs, which many will seek to avoid. Failure of these seals is evidenced by the dashpot damper oil draining every time you refill it, which leads to other issues. While you are at it, consider changing all the rubber components, including the diaphragms, spindle seals and the valve diaphragms and seals, in fact you may just as well buy a carburettor service kit and use it all….

If you really want to avoid all the above, especially tuning the carbs, then as a minimum, I advise removal and replacement of the plug and seal units, using the fuel resistant sealant as described. This is just possible in situ, but awkward. I may have some photos that show some of the components described if you wish, but I am not near my home PC at this moment.

Best of luck,

Regards,

Simon

[Lemans88]

Thank you Simon.

On returning to this forum today, I note that I had forgotten to thank you earlier.

The ignition problem remains.

I replaced the ignition amplifier since the last post & all seemed well last year including several journeys of 1.5 plus hours ( 25 -30 years ago I regularly travelled to Le Mans, no problem!).

Then today!! 4 or 5 miles before intermittent stuttering then total loss of engine power.

Only able to crawl home by a number of short halts ( to cool a little??) &/or first gear only & 4000 RPM.

Coil & amplifier too hot to touch.

Fuel pump apparently happy to tick up to pressure .

Would the simple junking of the original Opus system be the only realiable solution? Or is there another answer?

[vee12eman]

Hi again.
I have no experience of the OPUS unit, when restoring the car, I went straight to ReOPUS, sadly no longer available. However, I believe that when the OPUS starts to fail, replacement is the only answer. I’m not convinced that my ReOPUS is performing well now, some ten or eleven years later and may go for the SNG unit soon, but I need to save my pennies first…

One thing to try is cooling the hot units with a Bag of frozen peas and seeing if cooling one or other unit cures the problem, even if only temporarily. That might help you to diagnose.

Good luck and keep us updated.

[Lemans88]

Thanks.

Will try.

Really annoying as I was set for the SNG Barratt invitation hill climb at Shelsley Walsh in a couple of weeks & the car had been running well!

[phoenix]

Regarding tje hot coil usually I would say faulty HT leads. If they are breaking down they cause a higher resistance making the coil work harder and overheat.