Cold Start Issues

[Mike J]

Engine turns (occasionally) but doesn't fire. Have Webers and have checked the choke is working OK. Have recently replaced coil HT leads and distributor. After trying to start for about 3 mins when I return to the car it generally fires up. Fuel pump working ok. I have electric ignition which again works fine when running. This is a new problem pretty much since changing electrics. I'm sure someone has some idea.

Mike

[wilf]

Did this start immediately after changing the distributor? If so, I would suspect timing.

[davidf]

Could it be a problem with fuel getting to the carb, such as filter or a partially blocked line? It sounds like it takes time for the float chamber to fil (assuming a Weber has a float chamber).

[Mike J]

Thanks Both. Timing is where it was before about 15 btdc. New fuel filters from pump and in engine bay. I think this car just likes my wallet. Other car Subi Outback now playing up. So bought a new Starter for Stag as will need to use this for work. Or will have to use the horse.

[barkerwilliams]

As per David F the Stag is a large engine that enjoys boiling off the fuel in the carbs and a cold start sometime later the carbs take some time to refill,
I particularly noticed this when switching from the original points SU to a new electronic points pump which took an inordinately long time, (2 minutes or more).
Eventually I reverted back to the mechanical SU pump and the ticking stops after a few seconds.

Can you hear the pump ticking and does it stop before you crank the engine?

Does your boot vaguely smell of petrol? A faintly leaking seal on the tank fuel line on the fuel pump will allow air into the pump and break the vacuum between pump and tank meaning the pump then has to pump for longer to re-establish the tank to pump head to begin pumping. As this line is not pressurised but a vacuum do not expect to see a leak.

As a last throw of the dice, particularly after the lockdown, then old fuel simply does not vaporise in a nice explosive way in a cold engine. Is the fuel newish?


Alan

[Mike J]

Thanks Alan . Yes the pump does tick and stops before I crank the engine. It did start later today first time actually . Gut feeling it is the Weber carbs. They are making a horrid hissing noise . So may be back to the Strombergs.

Mike

[DZP]

Hi Mike,
I am not sure what carb you have, but usually it is one twin-choke Weber on the Stag, like my 38DGMS.
The Webers do not like pumping of the accelerator prior to cold starting, as there is a mechanism that pumps neat fuel straight into the venturi.
So, it could be you are flooding the engine prior to starting if you follow the same routine as the Strombies and floor the accelerator when applying the choke.
Check a spark plug when the engine doesn't start, you may find it is wet if you are flooding the engine.
With the Weber, do not press the accelerator, apply 3/4 choke and once started go to 1/2 choke.

The other thought I had is that the 12v feed to the coil during cranking is not connected.
With standard ignition you have a 12v ignition feeding about 8v to a 6v coil via a dropper resistor or wire (MK II).
When you crank the engine then 12v is fed to the coil via the starter motor circuit, to provide an extra boost during starting.
I think it is the white/orange wire, but check the circuit diagram to be sure.

I hope that helps,
Den

[jbuckl]

Recently fitted a powerspark, only to find the spark was weak.
spark became much improved after a missing baseplate earth wire was added. One to check?
oh & +1 for dzp’s post re 6v & 12v & ballast voltage/cranking voltage.
check starter connection for the 12v during cranking is tight.
consider testing with a Hotwire for a short time to the coil +ve, direct from battery, or fuse 1 or 2

[Mike J]

Thanks both for this. Have checked wiring around the coil and cleaned contacts. The gods must be with me it started . I think it was a combination of wiring and flooding. Just out of interest what BTDC are you running at ? Im on 15 degrees. Is this possibly too advanced.

Thank you very much for the help. Fitting new starter now.

Mike

[wilf]

I run at 14btdc, book figure for mine is 12btdc. Engine runs better with a touch more advance IMHO. If yours does not "pink", and idles OK, then you are probably OK.