Lights, music, inaction
Danny revels in the noise but ends up driving blind
Blatting around in the Jensen has been just as much fun as you would expect. It is a truly dirty pleasure and I still can’t get out of it without doing at least two glances over the shoulder before walking into a lamp post – it is that beautiful. But the relationship has been bittersweet.
The petrol side still needs to be correctly set up and I’ve gone as far as I can with the current carburettor, a Holley Street Avenger 650 CFM. It over-fuels and it needs rejetting, or I need to sort the 600cfm Edelbrock that I fitted over summer (before it started leaking).
This nearly happened after I was contacted by reader, Paul Holtom. He has a lot of experience with Edelbrock Performer and AVS series carbs, which are the old Carter AFB carbs rebranded. The Edelbrock was leaking fuel due to the fuel level in the float chamber being too high and that that was caused by one of three things: fuel pressure, float valves not seating correctly or float height incorrectly adjusted.
Paul invited me down for a day’s tuning, he has a full set of spares and all available metering rods and jets. I jumped at it. Then things got really interesting. Paul, and his mate Pete, have tuned many of these carbs using an air fuel ratio meter that requires a lambda boss to be fitted to the exhaust on one bank of cylinders. My ears pricked up. I love clever modern cheats that make old mechanicals run at their most efficient.
So I prepared HOF 1 for a trip down to their workshop for a day of play. Pete would work on the ignition side of the engine setting and optimising the ignition advance at cruising and total ‘all in’ advance. He also would help with tuning the carb using his, wait for it, lap top with all fuel metering rod and jet combinations.
By welding a lambda boss to my exhaust in order to fit the air fuel ratio meter necessary for tuning, it would be precisely and immediately measurable with tuning carried out at idle, road test at cruise, acceleration and wide-open throttle – all the conditions the carb encounters.
The tunable parts of the Edelbrock performer are the fuel jets, primary and secondary, the metering rods which are held down in the primary jets by vacuum which compresses the metering rod springs - the values of which are changeable within a range. The accelerator pump stroke is
also variable. With a computer plugged into a Lambda sensor, all of the above could be played with to achieve near perfection. I was on my way before I put the phone down.
A long night
The fun began as I left home, when all the lights went out. I was driving down to Paul’s place in Thatcham from my home near Cambridge, and was doing so late in the evening so as to avoid M25 hold ups and other Jensen-unfriendly pinch points. I switched the lights on and off, nothing. Then, in time-honoured fashion, I hit the dashboard. The lights flickered. Bad connection somewhere. I pulled the switch out and wiggled the connections. A small flash and a buzz, then all the lights came back on. I popped the switch back in and went on my way.
So far I’ve kept my Jensening to local journeys along with occasional work commutes – this would be the longest journey by far. Half an hour in, it was going splendidly. The noise was good, the petrol consumption extravagant and the grin on my face, wide. Heading along the A505, uphill through the tunnel at Baldock, HOF 1 created the finest racket any car of mine has ever produced. It was like I was driving a Spitfire… a real one. Next, down the A1 and onto the M25.
The first time I noticed an issue was when the lights started to do the flickery thing that usually signifies the voltage regulator on the alternator is coughing its last. I ignored it and pressed on. Then the dashboard lights went out and I got a slight whiff of hot plastic… but no smoke. So I pressed on.
Then a friendly young chap in a Clio pulled alongside at speed and told me that I had no rear lights. Time to find refuge. I pulled off at the M40 junction and parked on the slip road. No rear lights, but headlights and brake lights OK. Time to investigate.
I pulled the light switch again to discover it was hot and partially
‘The fun began as I left home, when all the lights went out’
melted. It was also impossible to switch the headlights off without disconnecting the live feed, the spade connector of which was burnt.
Roadside recovery
I called the AA, and then I called Paul. I wasn’t going to risk further damage by lashing something up. It looked like the circuit was earthing itself through the switch, which had melted before a fuse had gone. By 4.30am the AA had delivered me back home. I woke up the neighbours by starting the car to drive it into the garage. Then I put it under a sheet.
Next day, after a lie in, I decided to get back on the bike and drive the naughty Interceptor to the workshop for electrical probing. Literally two miles from home the throttle cable snapped at the pedal end. You couldn’t make it up. If I had lashed something up the previous night I would have made it back to the M25, that’s all.
Two weeks on I have fitted a new cable and done a daytime test run. All is well but the rev counter goes wild every time I use an electrical component. I don’t feel qualified to research this further so I’m need of an auto-sparky who can speak Jensen. Help gratefully received.
danny.hopkins@practicalclassics.co.uk