tried to start my 3.5 petrol classic and turns over fast as you like but wont start. disconnected plug lead and held over block and got a nice fat orange spark as it turns over. slackened off fuel line to carb and got wet fingers so tightened back up.went through haynes fault finding and says check between +ve battery terminal and -ve coil connection with ignition off and should be zero volts. Ive got 12.5 same as battery. manual says if voltage present change distributor amplifier, but as this is measuring across coil and switch surely this should be 12v with ignition off.Anyone any ideas

Well your first problem is you want a big Blue spark not an orange one.

thought as much, looking for a new coil in morning, just confused by the switch off and test from battery to coil -ve.

Ok start at the simple things first, Spark, fuel, as said a blue spark is what you want.
if I remember correctly the choke is on one carb only, check the linkage, OK, remove the u pipe to the air filter, get someone to crank the engine and (be brave) hold your hand over the carb inlet, This creates a massive depression and draws the fuel through the carb.

if it fires remove it quickly. If it fires it proves you are not getting fuel into the engine. Carb problems, sometimes old petrol will not fire. Too thick an oil in the dash pot will stop the slide lifting also. Let us know how you get on. Then we will go through the ignition if needed.

went through haynes fault finding and says check between +ve battery terminal and -ve coil connection with ignition off and should be zero volts. Ive got 12.5 same as battery. manual says if voltage present change distributor amplifier, but as this is measuring across coil and switch surely this should be 12v with ignition off.Anyone any ideas

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Ignition on.
There should be bat voltage to the coil + and the --, when it switches the – will go dead collapsing the fields in the coil and causing a spark through the secondary (HT)
I hope this makes sense.

Simple explanation of system
Rotating reluctor produces a spark, this spark is amplified by amplifier and drives the negative of the coil to ground, thus producing spark at plug.

Common ignition problems are ........

Non genuine spares fitted to ignition system, in particular rotor arm,dizzy cap and leads causing....
Rotor arm shorts through brass contact reducing spark
Dizzy shorts causing poor spark
Leads break down causing poor / intermittent spark
Relace all with genuine Lucas or Bosch

Stuck or fallen off bob weights.... twist rotor arm , should spring back

Amplifier, usually fails open circuit... no spark at all.
Repalace with new type, ( do not overtighten ) about £24 with grease, new plug and crimps

Reluctor coil fails o/c on lead ends or internally ... replace ...Expensive

If you remove the dizzy make certain you mark the position of the rotor arm before you remove.... ( Take a picture ) and mark the body of dizzy to block.
It can be replaced 180 deg out and will not work at all.


Check connections to all ignition components, push home and re-crimp where required

Try removing condenser while you trace fault, these can short out.

Other common faults apart from pump etc are coolant sensor, if this fails you may not be able to start easily and when you do the car will probably run ok while hot but not start again when cold. Shows up as flooded plugs

Don't forget to check all air hoses for leaks and check,clean or replace crank case breather filter


Good Luck
Fred

Other common faults apart from pump etc are coolant sensor, if this fails you may not be able to start easily and when you do the will probably run ok while hot but not start again when cold.

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I agree with all of your post except the temp sensor bit, I think you might be on about the fuel injected system.

Well spotted
Should have read the thread properly

took spark plug out last night and although has been turning over without firing all day plug was nice sandy colour but dry. so followed advice from etc7867 and placed hand over carb with u bend removed and it started but wont idle goes ok with revs on but coughs to a halt as soon as you leave it. looks like i will be removing carbs when i get home from work. Was running fine last week so dont think its bad fuel and fuel pump is getting fuel to carb fuel inlet. Had some fuel coming out of carb overflow when ignition on so possibly float problem??
Thanks to all for your help on this, It was driving me mad

Ok so it looks like fuel, Your fuel pump ticking away? Your fuel filter clean? Its unlikely both carbs are going off at the same time unless you have no filter in the system.
Did you check the choke linkage?
With the petrol feed pipe disconnected from the carb does the fuel flow out ok?

diconected fuel at carb and petrol shot everywhere so not a problem there. Did notice last week that with ignition on but engine not running fuel came out of the carb overflow so possible float problem?(although its not doing it now) will check the choke linkage on friday (working all day tomorrow)