Hot start problems

[RobinLegin]

Sorry everyone for bringing this up but post an engine rebuild, the car won’t start if switched off hot.
I will try changing the coil and see if that helps. Otherwise is there anyone in the SOC in Dorset who has the right tools and knows what to do who would work with me to fix this?

[barkerwilliams]

Robin,


Does the engine start when hot and only off for a minute or two only not starting after five minutes? That would point to fuel evaporating and causing a vapour lock, this seems fairly common on the Stag, pull into petrol station - fill car - go to pay and it's a pain to start, just takes long enough to get a vapour lock.


If the engine is hot and not starting I would

fit an ignition timing light to a couple of cylinders in turn and see if it detects the ignition spark and flashes - leads are usually long enough to reach the ignition key for cranking . whilst looking for the flash
If there is a spark and its not starting give it a squirt of easy start (£5) into the carbs and if the car then starts it is likely to be a vapour lock.

If the engine wont start then it is likely to be ignition related - coil, condenser if your still on points.
There are plenty of counterfeit spark plugs sold cheap on eBay (NGK- check their web pages) that only last a short time before breaking down, so perhaps a new set of plugs.
The rotor arm in the distributor should be red, the black ones were coloured with carbon to make them black and hey carbon is conductive and grounds the spark. Some rotor arms also have a rivet to hold the brass conductor in place this can be too long and earths the spark to the distributor metalwork.

Do not buy a replacement LUCAS ignition coil. They are not the same company that made them originally and are smaller and have a poor reputation,

If you have electronic points such as the Newtronic, Lumination etc then swapping out for diagnosis is not easy as the points base plate has been replaced.

Alan

[Robmsharp]

I had an intermittent problem with the engine hot that I eventually traced to the ballast wire supplying the coil (mines a Mk2). The symptoms caused the engine to misfire and run rough which would go away if the ignition was switched off for a few minutes, only for the symptoms to return a short while later.The cure was to fit a ballast resistor in place of the wire

[DJT]

I had an intermittent problem with the engine hot that I eventually traced to the ballast wire supplying the coil (mines a Mk2). The symptoms caused the engine to misfire and run rough which would go away if the ignition was switched off for a few minutes, only for the symptoms to return a short while later.The cure was to fit a ballast resistor in place of the wire

Took me ages to track down a similar fault a couple of years ago. Turned out to be the ballast wire connection to the coil. The wire had broken internally and it came apart with a slight tug. I just remade the connection.

[RobinLegin]

I have to confess that the engine fires up on the button, and runs beautifully smoothly thereon in. My suspicion is vapour lock, though I will try with the sparecoil I carrry.
one thing that perhaps is relevant is when starting up again I can hear the fuel pump ticking away non stop. Seems to suggest vaporisation of fuel?
loather to replace fuel pump with higher pressure unit, as this could lead to flooding the carbs. On the Alvis I carry an old domestic plastic bottle with a spray facility and squirt the fuel line and carbs. The évaporation of the water seems to disperse the vapour lock on that car. Not ideal.

[barkerwilliams]

Robin,

I do not believe there is a non-return valve in the fuel lines and apart from vaporising the fuel will also syphon back to the tank which is lower than the carbs. Vaporising will also pressurise the fuel lines and power the syphon action.

If you confirm it is fuel and it really bugs possibly the best solution would be to fit a fuel return line as in a post above in order that a hot start could begin with flushing cold fuel through the lines and bowl and sending any vapour back to the tank.

I agree there is no point in carrying a spare if you haven't tried it and proved it's good.

Alan

[Lingen]

Robin.
There is a "Non return valve" in the fuel pump, which will stop fuel going backwards into the tank. I have never seen vapourisation occur in Stag fuel lines if they are correctly located.. If it did, and the pump is ok, it ought to be capable of overcoming it. The commonest cause is leaking needle valves in the carb. float chambers. There is quite a lot of residual pressure in the fuel lines after switching off, and if they are faulty excess fuel can pour in to the inlet manifold, and flood the engine.
Or, as suggested above, the ballast system is not working. It is there precisely to try and overcome the problem of an excessively rich mixture when hot starting.
Mike.

[mallardstag]

Robin.
There is a "Non return valve" in the fuel pump, which will stop fuel going backwards into the tank. I have never seen vapourisation occur in Stag fuel lines if they are correctly located.. If it did, and the pump is ok, it ought to be capable of overcoming it. The commonest cause is leaking needle valves in the carb. float chambers. There is quite a lot of residual pressure in the fuel lines after switching off, and if they are faulty excess fuel can pour in to the inlet manifold, and flood the engine.
Or, as suggested above, the ballast system is not working. It is there precisely to try and overcome the problem of an excessively rich mixture when hot starting.
Mike.

+1
A common cause of this which leads to hot starting problems is fitting a replacement fuel pump with higher than standard output pressure (IIRC 2.7psi is required but many 'replacement' pumps have much higher than this). This causes the needle valves to leak after shutdown and consequent flooding problems until fuel has evaporated again.
Simon

[RobinLegin]

Robin.
There is a "Non return valve" in the fuel pump, which will stop fuel going backwards into the tank. I have never seen vapourisation occur in Stag fuel lines if they are correctly located.. If it did, and the pump is ok, it ought to be capable of overcoming it. The commonest cause is leaking needle valves in the carb. float chambers. There is quite a lot of residual pressure in the fuel lines after switching off, and if they are faulty excess fuel can pour in to the inlet manifold, and flood the engine.
Or, as suggested above, the ballast system is not working. It is there precisely to try and overcome the problem of an excessively rich mixture when hot starting.
Mike.

Mike,
how easy is this to fix? Do I have to take the whole carburettor apart? Or can I just access the float chambers in situ and replace the gasket and needle valve?
Easy on SU s but not really confident with Strombergs.

[Lingen]

Robin. You only need to get the float chambers off, which are each held in place by six set screws. The float is easily folded out of the way to give access for a small socket to unscrew the valve.
It is easiest to undo the nut securing the carburettor pedestal to the inlet manifold, and turn the whole assembly upside down to access the set screws. If you run the engine with the fuel pump inertia switch "Off", and wait for the carburettors to run dry, it will minimise the mess. Have lots of rag/paper to hand. You will need to check the float levels after fitting the new valves.
Having said all that, I would first check to see if the ballast system is working as that is a much simpler job. If it isn't, sort that out first, and see if the problem goes away.
Mike.

[Basilbrush14]

I have a similar problem but when hot it starts and runs fine, until I try to pull away, then it either stalls or feels like it is running on 4. This is both embarrassing and more importantly, a trifle dangerous when pulling out of side roads into traffic. Given a minute or so with wheels turning it picks up and runs fine. It is very frustrating. New electronic ignition, rebuilt carbs (stroms) and dissy. Fuel lines are steel braided and new fuel filter with pressure reg. has made no difference. It does it in the cold weather as well as the hot BUT not from a cold start and only after a 10 minute + stop when up to temp. When I find a cure I will post it but if anyone has suggestions they will be tried. It looks like TC will be worth a look.

[richardthestag]

to discount ignition related cause. when it will not start, run 12v feed from battery direct to coil +ive. if it starts straight up then ballast feed is most likely the issue. I ended up isolating the pink ballast feed and taking a fresh 12v feed from a white wire on the back of the fuseboard. I now run a 12v flamethrower coil. but no reason why you cannot stick with ballasted coil and retro fit a mk1 ballast block between white wire and coil +ive.

check that your coil is not touching the engine block / head. it needs fresh air all around it. an overheated coil will make the car difficult to start

if that is ok then I am inclined to think flooding. run engine up to temp, switch off and remove carb top and damper. is fuel coming through the jet hole at the bottom of the carb body?

I run my stag at about 2psi fuel pressure as it was doing exactly that ^ and flooding

[sujitroy]

Gents

Thanks for all your various thought provoking replies. I really appreciate you taking the time to write them.

Temperature Compensators
Having thought further about this the ones on the stag are set up. It's the ones on our GT6 which are screwed fully in as they simply would not balance. However, I will remove them off the Stag are check them out and adjust if required

Overflow / venting pipework
I will check for blockages as suggested

What have I replaced since the hot start issue arose?
As most of you will be aware I have spent January to July replacing wings, door skin, wheel arches etc and repainting the car. No work was performed on the engine systems. It had the first hot start incident on its very first decent run out after all that work was completed. Admittedly that run did coincide with 31+ degrees in the shade weather, a real scorcher. The car has also been suffering from a misfire since that first run out. After renewing the spark plugs and coil I finally tracked the cause of the misfire to the small earth cable inside the dizzy which connects the baseplate to the dizzy outer body. The cable had broken and as I pressed the throttle and the vacuum advance kicked in and moved the baseplate, the two halves of the cable separated causing a break in the circuit and a misfire. I took the car out for a 40 mile blast yesterday evening and she behaved perfectly and the ignition system now seems to be operatingly correctly.

In the meantime I will do as Neil suggests and switch off the pump a little while before I switch the engine off and where convenient pop the bonnet.

I have entered this years RBRR using our Stag and given that we will be travelling 2,100 miles in 48 hours the engine is not going to have any opportunity to cool down and there will be multiple hot starts involved so I want to sort this issue out within the next few weeks.

Thanks again for your assistance

Regards

Bruce

Bruce,
Did you resolve the hot start with any of the suggestions mentioned?

Sujit

[PeteJS]

I had this problem, last year and after much investigation, it was as simple as the breather 'tee' piece on the air box stub pipe was pushed on too far, thus blocking the breather pipe to one carb.
I have had no issues since I positioned the 'tee' correctly.

[Donkey]

I had this problem, last year and after much investigation, it was as simple as the breather 'tee' piece on the air box stub pipe was pushed on too far, thus blocking the breather pipe to one carb.
I have had no issues since I positioned the 'tee' correctly.

Most interesting Pete.
Having continued to try and resolve my issue and come down on the side of "vaporisation", I read the above and immediately shot down to the garage and found exactly as you'd described. If you're right in your assertion, then there's a drink in the post.
Regards,

Brian