Now that we have completed our Jag Mk/2 brake system for the third time, we are left with checking our cars tune, putting on a thermostat gasket and some carpet work. Our car is a 67 Mk/2 3.4 with dual SU carbs. Heres what we did to renew our fuel system and how to adjust the SUs. We installed our reconditioned gas tank and a new electric fuel pump, blew out the lines and cleaned the fuel filter screen. All this was necessary due to the Jag's not having been driven for about ten years. We drove it before we removed the tank and could tell it was running a little rough, but thought we could get one more trip around the block before pulling the carburetors for rebuild. With all of the new fuel components on, we tried to start the car, but immediately smelled gas! It was running out of both drip tubes! We had checked our spark and knew we had good spark out of the plugs. The problem was clearly in the carburetors, thinking it to be stuck floats or needle valves from trash previously in the tank. If we did have to remove the carburetors, it would be a good time to clean up the engine compartment. The twin SU's are located on the right side of the engine, and once removed would give us easy access to clean, paint and detail the engine, which is something we had already planned on doing. I researched the Jaguar club's website and found all of the engine compartment's restoration details. Jaguar engines of this period color-coded the heads, and the 3.4's used a light blue. I also found pictures of a low-mileage 3.4 with OEM paint still on the head. It looked very much like the blue Buick used in the 1940's through '53 on their straight 8's, so I will use the Buick paint on the heads, gloss black on the block and clean up the finned aluminum oil pan. The exhaust manifold was originally porcelain (mine is long-gone), so I will clean the exhaust manifold with a die grinder and wire brush, and paint it with hi-gloss black exhaust manifold paint from Bill Hirsch*. The racy aluminum dual overhead cam covers and chrome acorn nuts with copper washers will be buffed, the coil and bracket are to be silver and the air cleaner is silver "hammered" paint.
This will also be a good time to tune it up. We'll replace the distributor cap, points, condenser and rotor, all from Vintage Jaguar*. When replacing these rotors, use an OEM rotor. Some of the aftermarket ones have a brass pointer that is too wide and can hit the cap's brass contacts and break the rotor. This can be remedied by taking off the cap, setting the rotor in the cap, turning it around to see where it is hitting and grinding a little off, OR you can go OEM.
The original spark plug wires had Champion plastic wire ends at the plug with suppressors in them. I believe a car with a points-and-condenser ignition system should use non-resistor spark plugs and stranded or solid core wires. Electronic ignition systems should have resistor plugs and resistor wires. Using non-resistor plugs and stranded wires will get the recommended 20,000 volts to the spark plugs. The new non-resistor plugs are Champion N12YC. I bought mine at Advance Auto Parts. They can also be found online. The OEM plugs were Champion UN-12Y, and are no longer made. For the plug wires, I make my own, buying stranded spark plug wires by the foot and get it from Antique Auto Parts Cellar*.
With a game plan on the engine compartment, it was time to go to the carburetors.
ABOUT THE CARBURETORS:
The Jaguar Mk2, 3.4 & 3.8 litre are fitted with twin SU-HD.6 carburetors. The HD type differs from the earlier SU's in that the jet glands are replaced by a flexible diaphragm, and idling mixture is done with a metering screw instead of a throttle disk. Before removing the carburetors, we called Daytona Carburetor* to go over removal, shipment and rebuilding. The decision was made to send them as a unit and get them back as a unit, which would provide less chance of something being out of adjustment or getting lost in the process. Daytona has rebuilt our carburetors for years, and when we get them back they are tested and adjusted and ready to run. As always, we took photos of every detail of the carbs and hookups, and set up a 5-gallon plastic bucket for the parts we removed, labeling each one.
We first disconnected the battery, then removed the air cleaner and the intake pipe by unscrewing the set screws attaching the pipe to the carburetors. We removed both banjo bolts and the four fiber washers from the float chambers. Care must be taken when removing the springs and gauze filters at the banjo bolts, (noting that the springs go in small end first). Next, we removed the cover on the auxiliary starting solenoid on the side of the front carburetor (this unit is wired to a thermo sender that opens and closes the carbs' chokes), and marked and disconnected the wires to it, removed the clip attaching the overflow pipes from the float chambers to the oil filter mounting screw and disconnected the union connecting the starter pipe to the auxiliary starter carburetor. We then removed the cotter pin, plain spring washers from the connecting link pivot pins located on the manifold between the front and rear carbs and disconnected the throttle link rod joint from the ball pins on the bell crank lever, removed the four nuts and washers that hold down each carburetor to the intake manifold, then we carefully pulled the carb assembly out. Once all the photos and notes were completed, we packed the SU's up to send to Daytona. When they come back, if any adjustments are necessary, it would most likely be to tune the carbs and adjust the throttle control linkage setting. Here is the way to do that:
With compression, valve clearance, spark plug gap, point gap, spark plug wires, coil and vacuum advance all good, there are only two adjustments to tune the carburetors. 1. The slow running volume screw [A] that governs idle speed and 2. the mixture adjusting screw [B] governing mixture strength. The correct setting of the mixture at idle speed insures that the carbs are correctly adjusted throughout their entire range. To adjust mixture strength, back out both mixture screws [B] until the tops of the jets are flush with the jet bridge, then screw in mixture screws until jets start to move, then rotate 3 ½ turns further. Screw in the running volume screws [A] until they are fully down and back off 2 ½ turns, run the engine until it reaches normal operating temperature and listen with a stethoscope to each carb. Both should have an equal sucking sound. Rotate the slow running screws [A] until the carbs are synchronized (sucking equally) at 500 RPM's on cars with 3-speed and automatic transmissions, and 700 RPM's on cars with all synchro gear boxes. Just check the dash tachometer for this.
THROTTLE CONTROL LINKAGE SETTING:
When the carbs have been removed, or the throttle linkage disturbed, the control linkage must be checked (adjust with the air cleaner and intake pipe off). 1. Disconnect front carb coupling and rear carb throttle lever by releasing clamp bolts. Check that both butterflies are fully closed and that the rear carburetor coupling bolt is clearing the manifold nut. With both carbs fully closed, re-tighten front coupling, unscrew the intermediate throttle stop and push down on bell crank lever until center "A" is 1/16" below "A" line from center "B" to pivot center. When it is in position, screw down stop onto intermediate throttle lever and lock into position, then lock lever to carburetor spindle. Make sure that when the throttle is closed, the intermediate lever does not hit the fuel connector pipe. Now open the throttle fully and check to make sure both carbs are in the fully-opened position.
After we get our SU's back and set up, we will follow the maintenance schedule.
Every 2,500 miles: Lubricate the carburetors' piston dampers. To do this, unscrew the cap on top of each carburetor's suction chamber and lift out the damper valve attached to the cap. Fill the hollow piston spindle inside the suction chamber with SAE 20-weight motor oil.
Every 5,000 miles: Clean carburetor filter. The filter is attached at the top of the right side fender well. It's an "AC" with a glass bowl and flat gauze filter at its top. It does not require a paper element like its GM counterpart of the period. To clean the screen, back off the lock nut, swing the retaining clip to one side and remove the bowl. The rubber sealing washer between the top of the glass bowl and filter housing should be replaced.
Once the carburetors return, we will continue this. Watch for upcoming articles on the Mk2 for carburetor installation, tune up and chrome work. We will also have articles and features on American cars from Chevys to Packards.
Keep 'em driving!