Irecently had a visit from a fellow TSOAQ committee member to see if we could improve the slow running on his Triumph Spitfire. Since acquiring and completing the car he has experienced a number of fuel related problems most of which have now been resolved, however the slow speed running is still an issue.
The engine operates well whilst driving at normal speed, however as soon as you try to crawl along in first gear it copies our local marsupial and starts to ‘kangaroo’ down the road. I thought that the most likely reason would be carbs not balanced or that individual butterfly opening was not synchronised so I offered to have a look.
We checked all the obvious things first, including throttle opening and float levels, which were all correct. We then went through the basic tuning operation for a pair of SU’s. Main jets were raised to the bridge then screwed down the recommended distance and engine started so a flow meter could be used to balance the air flow through each carb. Mixture strength was then adjusted on each carb and checked by slightly raising each piston, then airflow rates again checked and butterfly openings synchronised.
The stationary engine appeared to operate perfectly but a road test revealed the same low-speed problems. Whilst the carbs are worn and could do with an overhaul, including new spindles and bushes, we are beginning to think that the problem is elsewhere, and that we should now look at the distributor operation and timing, so an upgrade from points to an electronic system is on the cards.
This month’s plan was to fit a 77°C thermostat in place of the standard 82°C unit fitted to the Stag after the engine rebuild. Whilst I had the cooling system partially drained I also intended to fit a secondary heater water shut-off valve in the engine bay. The original heater control valve seemed to have excess clearance between the body and plug which allows a slight constant bleed of hot water to the heater, which may be acceptable in some climates but not here in our temperatures.
Also when I finally commission the air conditioning system the last thing you need is heat emanating from the heating section. Also in conjunction with thermostat replacement the temperature switch for the Kenlowe electric fan requires adjustment to reduce the time it operates.
The car was raised on the lift to allow some water to be drained from the radiator. This was the first use of the lift since relocating to the new workshop. When I was having issues with the porous water pump cover and subsequent sealing of the inlet manifold, I fitted drain cocks in place of the drain plugs on the engine block to allow easy water
jacket drainage and these came in useful as they allowed quick simple partial radiator drainage. Access to the thermostat housing required removal of the air cleaner and I also removed the air duct from above the radiator to improve access to the hoses where I intended to fit the heater shut-off valve.
As one would expect, all items came apart easily. The three-way connection that I had fabricated during installation of the Stagweber header tank was also removed. Prior to fitting the replacement thermostat, I took the opportunity of checking the operation of new and old in a bath of hot water. Boiling water was added to a container and cooled to about 75°C and the two thermostats immersed. More boiling water was then added heating the bath and at 77 °C the new unit opened.
Adding more boiling water increased the temperature to 82°C but the old one hardly moved and required a further temperature increase to open. I am not sure whether this indicates an issue with the old unit or is just production variance. After cleaning up the sealing faces on the inlet manifold and a thermostat housing, the gasket was smeared with non-hardening sealant and used to fit the replacement thermostat. The two housing retaining bolts were gradually tightened, then torqued.
The long copper pipe leg of the fabricated Tee junction was shortened, allowing sufficient space to allow fitment of the heater valve between this and the stainless heater pipe using short sections of heater hose and worm drive clips. After replacing all hoses and tightening the clips, the cooling system was refilled ensuring both heater valves were in the open position. After checking for leaks the engine was started initially with no radiator cap so I could monitor the water level. When all appeared OK the cap was replaced and the engine allowed to warm up again, checking for leaks as the water pressure built up. After warm heater pipes confirmed that water was flowing through the heater matrix the car was taken on a short test drive. Whereas prior to the thermostat change the temperature stabilised at about 88°C it now appeared to be running at 8 or 9° less.
This was only a short test but as it was a warm day, about 37°C I was happy with the outcome. The performance now needs to be checked under variable conditions including hill work, and sitting in traffic after fast open road running.
Those who have followed the restoration may remember that I fitted a Racetech mechanical temperature gauge, so I know I have an accurate reading of the water exiting the RH cylinder head. After exiting the cylinder head the water flows through the inlet manifold where it cools slightly before reaching the thermostat so it is understandable that gauge reading is a few degrees above the thermostat setting.
Next month I will report on how the car performed on future outings. I also need to readjust the headlights. The lights were originally aligned after the car had covered a handful of kilometres, however when I was out the other evening both main and dip beams were very low.
I suspect the change is due to the new springs settling but as our new house is in a more rural area with areas of little or no street lights, good main beams are a priority, especially as there are Kangaroos in the area that have no road sense and will feed by the roadside around dawn and dusk.
The carbs on my pal’s Spitfire required tuning.
On its way home – improved running but not perfect.
The replacement 77° thermostat with an additional heater valve awaiting installation.
Removing the air filter allowed better access to the thermostat housing.
The first use of my ramp after installing it in my new workshop allowed easy access for radiator water drainage.
Air filter assembly replaced and ready for a test run. The heater valve is not too obvious.
Air duct was also removed to allow improved access to the hoses for fitting the heater valve. The copper pipe required shortening.
Prior to installation, the operation of new and old thermostats was compared.
Thermostat installed and heater valve squeezed into place.