Fuel getting to carbs, plugs are sparking, static timing looks right but it wont start - not even a cough

[Alastair Smith]

Haven't run the GT6 Mk1 for a while - it was running fine a few months ago - came to start it and it just won't.  Fuel is getting to carbs (just refurbed), static timing looks right (13 degs BTDC according to workshop manual, vernier adjuster in middle of travel, points just about to open), checked points gap, getting a spark, leads are in right order, engine turns over on starter motor but I can't get it to fire up. I must be doing something stupid or missing something. 

Can anyone suggest anything else to try please? I am completely at a loss. 

 

[Pete Lewis]

old question have    what was the last thing you touched ??

do you geta actual spark at the plugs   ,  as its sounds like points /wiring to /condensers/and firing order is on no1 compression stroke 

its easy to get things messed up when random twiddling starts to get the better of the enthusiasm 

Pete

[Alastair Smith]

Last thing I touched was to put the carbs back on when I got them back from the refurbisher. They ran them on a 2L engine at their end apparently so I assume they are set up well enough to at least get it to fire up. I tried turning it over with full choke and flooded them the first time so fuel is definitely getting to the carbs.

I get a spark at the plugs by holding it onto the engine block. How big/bright should it be? It's clearly visible but I would have imagined it being a bit brighter and bigger. Checked plug gaps. 

I checked the timing on no 1 compression stroke and it looks spot on. Plug leads definitely in right order - I tripled checked. I haven't check the condenser - don't know how to - could that be it? Why would that fail when it's sitting idle?

Totally stumped.

[RogerH]

Hi Alastair,

 very silly question but it has happened (not to me) - did you blank off the intake holes in the manifold when you removed the carbs - if so have you taken it out.

Also have you tried any form of 'Cold Start'  squirts

Roger

[poppyman]

Hi Alastair,

I had the very same thing on my 2500S, it would even fire and tickover, touch the throttle and it stopped. Eventually i changed the condensor...... started and ran perfectly. The previous weekend i had done close on 200 miles in it without missing a beat. Never had that sort of fault ever...

Tony.  

[Pete Lewis]

there have been some terrible condensers out there , is it fairly new ???

the  spark is often a dull less than inspiring 

has it run at all on the refurb carbs ????

is there any gasket or filter unknowingly covering any of the filter face breather holes ???

Pete

[dougbgt6]

Alastair.

13  degrees is for 5 star and too much for modern fuel, sometimes 7 or 8 is required depending on the slack in the mechanical system. As Pete says, are the gaskets right? One way is correct, but there are 3 other ways which are wrong. A can of Easy Start is good stuff, if it won't start with a squirt of that something's badly wrong. Did you change the manifold gasket? A leak here can kill ignition.

Doug

[Alastair Smith]

Thanks everyone.  I will look at all those options tomorrow.  I may just have blanked off the intakes to keep dust out.  Then I'll feel stupid!

[Pete Lewis]

a revisit to the last job you did often finds the culprit  rather than dive off all over the place 

Pete

[haggis]

Have you connected the carb breather yet? 
 

 

[Clive]

You have fuel, you have spark. It should do something....

On a new  engine etc, I have often got my glamorous assistant to turn the car over on the key while I twiddle with the dizzy. As in clamp undone, rotate through almost 90 degrees is possible. 

Have you taken the dizzy off at all? ot the leads? 180 out is very common.

Are the plugs getting wet?

Definitely no leaks in the manifold gaskets?

 

[ahebron]

Have this problem with my dads vintage car, everytime it is the plugs fouling due to him starting the car and running it for a minute or two without driving it.
Plugs swapped for dry clean ones and it starts fine.

You sparkpugs could be failing under load of compression

But I would replace the condenser

Just ordered a sparkplug cleaner and a spark plug tester from Mr Bezos old company to have a play with.

 

[JohnD]

People obsess about the condensor in the dizzy, without appreciating what it's for and how it can fail.

The distributor ignition system, and so much else in the automobile electrical sytem that was the rule until electronics, was invented by Charles Kettering before the First World War.       The single lapse of his invention was that the points wore  out after a few hundred miles, because of 'arcing', the electrical spark between them that eroded the metal.       A Condensor across the points reduces arcing and delays wear, so that they last for many thousands of miles.     It does nothing else.

Condensors fail, but in only two ways.    They can fail to condense, allowing arcing and points wear, or they can fail by short circuiting.     A condensor consists of leaves of metal foil  separated by an insulator.   If the insulator fails, then there is contact between the foils and current flows through the condensor, around the points.     They do not make and break the circuit through the ignition coil and there is no spark to run the engine.

If you suspect your condensor, just remove it!    You can always put it back or replace it later.     You will get more arcing at the points, but ignition sparks will be made as normal.

If you want to be technical, use a multimeter.    Set to a low resistance, a working condensor will show a rapidly rising value, while a short circuited one shows a fixed and very low resistance.

Good luck!

JOhn

[Pete Lewis]

yes some after market copies were cut open and there should be about 3 mtr  of foil wound tightly inside  the failed 

copies had orange wires and only 1mtr of foil inside ( the orange may not be any clue  )

 

Pete

[A TR7 16V]

I would also say that the easy test is to take the condenser out.

As to there being a load of crap condensers around: I got two new condensers from Bad Boy Classics a little while ago, both of which failed sequentially in about a week of daily driving - which led me off down many rabbit holes and the fitting of a new coil I didn't need. I got one from the Distributor Doctor that seems fine - though the lead were a bit short for the Doly Sprint.

But I would also add there can be a few more variations on the failure modes than open and short circuit.  Like, for example, the dielectric breaking down at higher voltages and different temperatures. So it can measure okay and yet still cause there to be an insufficient spark.

Some may ask what's the dialectic: A capacitor (as the more modern terms is) is simply a pair of plates separated by an insulating material called a dielectric. The capacitance (how much voltage stores how much charge, in effect, how many electrons) depends on the area of the plates, the distance between them, and the properties of the dielectric (esp. its relative permeability). That dielectric can be one of many materials, including air, paper, and various plastics. A possibly surprising choice is water, as pure water is not a conductor (which is why polaroid lenses cut reflected glare off water). My EM lecturer at Uni reckoned a 1 Farad air gap capacitor, which would store 1 Coulomb of charge (about 6,241,509,128,999,772,821.6 electrons) at 1 Volt, would just fit in Moscow's Red Square. But that's very probably FTMI.

 

[dougbgt6]

Supposedly a photo of the capacitor used by Marconi in his transatlantic radio experiments.

Doug

[A TR7 16V]

Capacitors out of the ark for getting arcs out of capacitors. 

Bet the discharge from them Hertz.

Graham

[dougbgt6]

Marconi's capacitor was a disappointing 1.8 µ Farads, but a whopping 40,000 volts and had an air dielectric. 

Doug