Thanks, Jochen for the “plug” !!! Weak pun not intended .
Ian. Old time mechanics had bump devices to crank the engine while under the bonnett. Usually done at the starter solenoid. A handle with a thump operated switch. I have a couple in my gear… From the old days…
You can do it on these cars at the starter relay.
Jump 12v+ to the RW wire that leads from the relay down to the starter. CAVEAT, the car will start and run in gear and depart!!!
Bump the enigne over in quick applications to get the rubbing block on a high point on the cam.
Remove the HT from the center post on distributor. Connect it to a plug ala Frank/s method of or merely lay it to allow any spark to jump to ground.
OK ? But not quite there. Replace the HT. Remove any of the spark plug HTs. Crank again. Spark?
OK, on to other diagnostics.
Not OK, Bad coil, points or merely poor connectors or wires. Break out the power checker and ohm meter…
The only exception I have found where there is no ballast resistor with mechanical points is when the coil ‘+’ is fed through the tachometer. Check your diagram to see if this is your set-up? If so; it adds a complication…
As a minimum verify theat the points are clean, not pitted - which may interfere with gap setting. With excessive gap, the coil may get too little dwell angle for proper operation. The gap will also interfere with ignition timing. One way of setting gaps without turning the engine is to loosen the clamp and turn the distributor. However, dist body must be marked to return it to the proper position - for correct ignition timing.
As an aside; ign voltage is depending on how fast the coil ground connection is broken by the points - unavoidable arcing as the points starts to open delays the break and reduces the ign voltage. The capacitor fitted reduces the arcing, reducing points wear - but the capacitor itself also slows the break. The ‘6V/12V’ idea was that a ‘6V’ coil with a 12V electric system theoretically doubles ign voltage. However, running a ‘6V’ coil continuously at 12V leads to coil overheating - hence the external resistor with bypass. Also; ign voltage bridges the spark plug gap - but it is current that give the spark the ‘blue’ energy…
That said; sorting out weak sparking is not necessarily easy - but an engine may run well enough on a weak spark…
I now have a better spark after changing the coil but the car still wont start. It has the solenoid operated third carb on the front carb and given its cold, enrichment might be the problem. I hear the solenoid operate for a second or two then it drops off and on again even without the engine running ie with no rise in temperature.should it stay engaged until the engine warms up? How do I test if it is working and is there a way of manually choking the car to get it started?
That would be the Automatic Starting Carb for the SUs, Ian…?
Indeed, it should open while the engine is warming up. And operating; there should be a pronounced hiss, indicating air is passing through. It’s controlled by a a thermostatic switch in the coolant. . As the carbs are adjusted to run a hot engine - the ASC adds fuel and air to fatten the mixture and incease cold idle…
Check that there is power to the ASC and check connection to the thermostatic switch - shorting to ground should operate the ASC…
When working, enrichment is adjustable with the engine hot.
CAVEAT, the car will start and run in gear and depart!!!
Haha that NEARLY happened to me at I time I was having trouble with the relay there. I hit that red/white with hot and then found out the reason it wouldn’t start was that I had left it in drive when I got out. Fortunately it only rolled about 6 inches into the parking bumper.
I’m not sure if this information is still relevant with regard to this issue, but there is any easy, foolproof way of checking spark that requires no tools and can be performed on the side of the road, if necessary. Disconnect the centre lead from the top of the distributor cap, and then remove the cap itself. With the ignition on, manually open and close the points while holding the end of the H\T lead near an earth on the engine. Each time the points are opened, there should be a large, fat spark to earth; it should cross at least 5mm, probably a cm.You should see and hear it. If there is a good spark there, a fault, if it exists, is further downstream. The spark from the coil to distributor lead is fed into the dist cap, via carbon rod to the top of the rotor and thence to whichever sparkplug lead the rotor is adjacent and ultimately its plug lead and plug. Any failure is probably in the distributor cap, rotor or the spring loaded carbon rod that pushes down on the rotor top.Often the carbon rod sticks in the cap, or more likely, the cap is cracked and moisture is causing tracking. This tends to cause missfiring rather than total failure, however. A good place to start looking, though.
Car is now running, not sure exactly what I fixed but a complete rebuild of the ignition circuit and a check of the operation of the starter carb and then she started right up and is running fine tick-over around 450 rpm.
Hi Frank
I tried that following manual but neither slow running screw makes any difference. hot the engine runs at around 600 rpm and is very smooth front carb slow running screw is fully down and jammed, rear carb screw is free but I can turn it fully out and fully in and no increase or decrease. Plug colours are perfect and no sign of rich running. Does this mean a vacuum leak somewhere maybe?
its worth check your ignition timing to see if its in spec, at idle & 3000rpm
then, with the engine somewhat warmed, the holdown bolt pre-loosened a bit, and dizzy position well marked, you can rotate the dizzy by hand with engine running, for optimal smoothness and idle speed
A first step is to use the crude ‘hose-to-the’ at each carb intake, Ian - to check is the carbs are in sync.
That the carbs’ idle screws are set different is a fault in itself - and abnormal symptoms to be expected. That idle does not respond to the rear’s idle screw is odd - but may have several causes besides a possible air leak…
