MkIV Poor Starting – where to start!

[Rick2112]

Afternoon All

 

Spit is notoriously difficult to start after being left for a few days (and getting worse although it's never been good)

• if I run the engine every day it’s not too bad and starts after a couple of attempts
• car runs fine when I’ve actually managed to start - but would benefit from a mild tune up
• if I start when it’s warm it goes on the button

If I then leave for a few days before starting again it just keeps turning over and over – eventually it will burble slightly – then a little more (could be up to ten or twenty attempts!) before it finally just about runs but needs to be coached into running properly by blipping the accelerator pedal gently a few times. Once it is running its fine.

 

Starter motor seems OK and battery is good – plenty of power to turn over the engine

 

Carbs are rebuilt and all runs fine once car started (if slightly rich) – petrol is fresh and choke operation ‘seems’ fine with everything lubricated and pulling/returning as it should.

 

Ignition is one I inherited with the car – Mobelec Magnum Electronic Ignition – with a Lucas Super coil so both well over 20 years old now.  Leads are Magnecor and fine. Dis cap and rotor arm are both new – no difference with old cap and rotor.

 

Distributor I’ve never actually touched – but as it’s a late MkIV I’m assuming this to be a Delco one

 

Question is where do I start – I’m clearly getting a spark – so is this just a poor one when the engine is cold and has stood for a few days? Maybe an earth problem on the ignition where the main unit is mounted? Or should I be looking elsewhere maybe at the choke even through it appears ok?

 

Any pointers (or maybe points!) appreciated

Rick

[Pete Lewis]

two thoughts here

 

you sound like you have a ballasted  6v system and have lost the feed when cranking

 

on a mkIV there is a white pink wire feeds the coil  from the ign switch when 'running'    this drops the feed to 6-8volts to the coils +ve terminal

when you crank there is a white yellow wire comes from the starter solenoid to the coil +pos terminal this gives you a voltage boost when cranking

if this has decided to die then you may not get any decent spark when cranking and the  engine tries to catch but stops as soon as you release the key 

 

have a look at these ,  if you have a meter the ballast whit pink will not show the drop in voltage unless the coil is energised it will show battery voltage 

and all becomes head scratching .

 

if theres a low coil primery voltage  the  dizzy elec module may not operate ,

 

try jumping a 12v from the battery direct to the coil +pos  

 

2.

 whilst the carbs have been refurbed,  do check the choke is really pulling the jets down fully, cold engines must have some choke enrichment or it wont start , again continual cranking fills the manifold and when its over rich will start and run poorly, then die , 

 

pete

[JohnD]

If

"if I run the engine every day it’s not too bad and starts after a couple of attempts

car runs fine when I’ve actually managed to start - but would benefit from a mild tune up

if I start when it’s warm it goes on the button"

 

then the problem is fuelling.  Either fuel is draining back towards the tank on standing, or the fuel in the float chambers is evaporating.

 

Get an electric pump, wire it to it's own switch, via the ignition switch.

Turn it on for a few seconds before you try to start.

Voila!

 

John

[dougbgt6]

Yeh, I thought drain back. Leave it a couple of days, disconnect the fuel line at the carbs and direct it into a jam jar. Turn the engine over, fuel straight away, it's the carbs, Long delay, it's further back. Repair kit for the pump and check the fuel line, particularly the short rubber sections. One below the fuel pump and one on the chassis in the passenger side rear wheel arch.

[Rick2112]

Thanks Gents

 

Few things to have a think about there - and I'll probably give them all a try over the next week or two as I suspect an element of both could apply.

 

Electric fuel pump is something I've considered previously after purchasing an extremely poor quality mechanical pump from a Triumph parts supplier - ended up putting my old one back on with new gaskets.

 

What stopped me was uncertainty around where to position the pump at the rear of the car as I don't really want it in the boot + how to fit a safety cut-off + whether I would need to put a regulator in line to adjust to the correct pressure.

 

Anyhow - I've got something to work with now prior to having to make that decision - thanks again!