Car stops when hot and won't restart
Car judders to a halt but later restarts
Idle speed seems too fast after the choke has been put back in
Hesitation or flat spot while accelerating
This can often happen with a slightly blowing exhaust. If you stick a vacuum gauge on and note the reading when the engine is idling, and then blip the throttle, you can see the vacuum fall away rapidly and recover slowly. An exhaust leak can reduce the idle vacuum, particularly if it is close to the head.
The 38DGAS/MS carb with the anti-stall device (looks like a second accelerator pump on the left-hand side of the carb float chamber) requires a vacuum in order to squirt some fuel into the barrels when it detects the engine is about to stall. If the little plastic or rubber pipe connecting the anti-stall diaphragm to the base of the carb is perished or leaking you will get a similar problem.
Get a length of garden hose about 4 feet long, place one end to an ear, and put the other end to each of the six exhaust outlets in the head, see if you can hear a louder chuffing noise at one of them, and check the manifold to down-pipe joint as well.
Checking for vacuum leaks in the carb can also be done by listening with the hose, but the engine noise will drown out subtle leaks. Instead, use a can of WD40 with the plastic tube and spray small amounts at critical joins and junctions around the carb while the engine is ticking-over. A sudden rise in revs followed by a settle back to idle means that you just sprayed at a vacuum leak point.
Finally, don't overlook the anti-stall device itself. If the diaphragm is perished or the spring weak it won't do enough to keep the engine running.
Don't confine yourself to the carb alone, also check the hose and connections between the inlet manifold and the servo; after all, it was stalling while braking hard that bought this topic up in the first place
As a last note, it took me a long time to completely cure this problem in HTX, despite fixing all the problems mentioned above. One day when I put the car on the diagnostics and was checking the idle settings and exhaust gas, I found that the engine RPM at idle was only 500, despite the tacho in the car claiming it was 650. Picking up the idle speed cured the last vestiges of the problem.
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(vapour-locking fuel line)
If the suction line to the petrol pump is too close to the pipe from the thermostat housing to the radiator, heat build-up in the fuel line can cause a vapour bubble to form, particularly if the fuel flow is slow (at idle) or non-existent. When this happens, the fuel pump suction stroke can cause the vapour bubble to expand and contract instead of pulling fuel along the line. The result is that the car will not restart until it has cooled down sufficiently for the vapour lock to have gone.
Cure - route the fuel suction pipe away from the water pipe. It should run up the left suspension tower. It should not be necessary to shield or lag the rubber pipe that connects the fuel line to the pump suction if a clearance of at least 1 inch is maintained between the fuel pipes and the water pipe.
If the car didn't stop of it's own accord, but simply won't restart again until it's cooled down a bit, (typically in a petrol station after filling up), the cause could be the auxiliary starting circuit. See the starting page problem Starter spins the engine but it won't fire (not enough spark)
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This problem should not normally occur if you have the standard air-filter, and have the correct Winter/Summer setting on the earlier casings. ( Check that this problem is not due to fuel vapour-locking when the engine has got hot Car stops when hot and won't restart until some time later by considering the circumstances in which the problem has occurred )
Carb-icing occurs in very damp weather, when the vacuum created as the mixture passes the throttle butterfly causes a temperature drop, and the moisture freezes out. The car becomes more and more reluctant to run smoothly, although sometimes fully opening the throttle causes it to pick up, not a good in thing to do in fog. After juddering to a halt beside the road and failing to find anything wrong under the bonnet, the car will start and run as though nothing had happened to it. Very often, you can drive the remainder of your journey without a recurrance of the fault.
If you have a pancake airfilter, consider changing back to the standard metal canister, because the snorkel nozzle on them will hold enough heat to warm the air up as it enters the carb. SE6's have a vacuum fitting to close a flap when a themostat in the airfilter detects cold air, and draw in warm air from the exhausts. SE5/5A owners have to manually set the flap to either cold or warm air intake.
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Sometimes carb-icing can show up in another way, the engine is running smoothly enough until you pull up at a road junction, and then the revs stay at 2000 and will not drop, even when the choke is fully in. This occurs when ice forming on the throttle butterflies hold them slightly open. In my SE5 this happens if I do not warm the car up enough before driving off and climbing 400 feet up the hill to Shaftesbury, even if the manual flap is set to warm air. If you feel the carb body just behind the throttle quadrants, it will be ice-cold.
Once the engine has warmed up sufficiently, the heat soaking into the carb will melt any ice that has formed, and prevent further ice formation.
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The car starts pefectly every time, and behaves faultlessly until you put your foot down to overtake someone, and it starts to die as the revs go up over 3000. Easing back slightly cures the problem, changing down or flicking overdrive on also cures the problem, until the revs go up again.
This is unlikely to be fuel starvation, but not impossible, so check the plugs for a nice tan colour anyway. When I first had this problem I was convinced that the power valve in the carb was faulty, but an overhaul found no problems, and the fault was still there.
It was a lot simpler than I had thought. Take a good look at the points. Forget what the dwell-meter is telling you, push the fibre heel away from the distributor cam and look at the points. Any grey build-up, or any cup and pit formation, and that's the obvious problem. Less obvious, and harder to tell, is points-bounce, but the cure is the same - change them, and the condensor at the same time.
In my case I had been trying to see just how long a set of points would last. I had got up to 22,000 miles, so I feel I got my money's worth, I just regret all those lost overtaking oppurtunities
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Assuming that this is not a fuel pump fault, a blocked main jet, worn points or faulty condensor, a worn distributor will give a misfire as the engine speed increases. There are two main reasons :-
If you suspect that only one or two cylinders are misfiring, try using the timing light on each lead in turn, and for the cylinders whose firing positions do not line up with the marks, pick some other point on the pulley and look for variations.
There should not be any movement in the top of the distributor shaft, but I have managed to keep some of my cars running with a little play.
The second problem, giving intermittant firing, is when there is wear in the advance mechanisms. There are several things you should check
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The Weber 38 DG and 40DF carburettors are fixed-venturi, which means that the size of the aperture through which the air flows is fixed, unlike the SU and Stromberg where a dashpot varies the aperture size according to demand. If you remove the air filter lid and look down the barrels of the Weber you will see two smaller tubes within the main venturis. These are auxiliary venturis, whose job is to amplify the vacuum signal in the main venturis and draw fuel through the main jets. Between the two auxiliary venturis is a V-shaped discharge head which spays fuel from the accelerator pump against the outer edge of the auxiliary venturi tubes. If you move the throttle lever you should see two fine jets of fuel. The jets spray momentarily each time the throttle is opened by more than a certain amount. The extra fuel they throw into the barrels helps to richen the mixture for a short period. When the engine demand sucks in more air there is a short delay before the main jets supply the extra fuel required to keep the mixture at the correct ratio. Part of this delay is caused by the inertia of the petrol droplets, which are heavier than air, and therefore do not accelerate as quickly as the air. If not enough fuel is thrown into the manifold by the accelerator pump, the engine will stumble when the accelerator pedal is pressed, but pick up and run smoothly again after a short pause. If the accelerator pedal is gently and steadily depressed and the car increases speed smoothly, but misfires when the pedal is pushed quickly, there is possibly a problem with the accelerator pump.
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