Am I missing something obvious here?

[xvivalve]

We had trouble starting one of the late Mr Tilson's Dolomites at his house; sometimes it would run and run fine, and others it just wouldn't start, so for convenience I dragged it back to the Midlands and it is in a Mate's lock up in Northfield (only slightly less convenient in actual fact) and the thing still won't run!!

At first test up here, there was no spark at the plug. A cracked distributor cap was diagnosed and has been replaced with a known and tested good one and now we have a reasonable spark at both lead ends and plugs. The points are gapped and clean, sparking well, and we have fuel delivery with the float chambers having been primed with fresh fuel. It cranks readily, but without any ignition, not even a cough or two. I've tested the cap, leads and rotor arm currently on the car on another Sprint and they are all fine on that car.

It used to have a Maplin style ignition unit on it, but fearing that was where the fault lay, I stripped it out and returned it to standard.

I can't see that the timing is critically out as it ran so well before and nothing has happened to it in the mean time.

Any ideas?

[HQentity]

Where did you test the earth against? Does it definitely still have a good connection from the engine block? Is the mixture/choke ok? Anything preventing fuel getting from the float chambers? Probably all novice thoughts but thought I would try my best to help!

[matt of the vivas]

NGK plugs by any chance? If so try a fresh set. For some reason once they get flooded with fuel thats it... they appear to spark outside the combustion chamber but under pressure in the cylinder they just dont..

[Richard the old one]

Have you tried changing the condenser?

[xvivalve]

Earthed at various points, the spark was even strong enough to pass through the rocker cover paint. Earth strap is a bit frayed and could do with replacing, but it is earthing the block more than adequately. Fuel flow from chambers is fine as plugs get wet. Choke is fine.

Plugs are fancy Bosch iridium

Didn't touch the condenser on the basis of healthy spark, but I guess new points and condenser wouldn't hurt...

Coil got hot, but as to be expected after cranking for perhaps a couple of minutes cumulatively, and the HT side seemed fine...

[RichardHyde]

Leads connected to the wrong plugs ?

[dollyman]

You could try bypassing the electrics by running wires direct to the battery from the coil? If it starts? work your way back.
Tony.

[Carledo]

As I recall, Jon was a firm advocate of running 12v unballasted coils fed from the fusebox especially when using Ei. Is it possible the ballast lead has been reconnected someway somehow by someone and you are now trying to run an unballasted coil with a ballast resistor? I only ask, because you mentioned the coil getting hot with 2 mins cumulative cranking, it shouldn't really get hot with 2 mins CONTINUOUS cranking! Just a thought!

I also once met a 1500FWD that would give a brilliant spark at the points, which if checked resulted in a brilliant spark at the king lead end. Once the cap was refitted and the engine cranked however, you'd be lucky to get a single cough. It drove me mad for several days whilst I investigated less and less plausible reasons for it's failure to proceed. Finally, even though they looked perfect, I changed the points, that did it! Fired up first cough! I really HATE it when this sort of thing happens! To this day I still have no plausible explanation for why the points would work perfectly when the engine was spun with the cap off, but with the cap replaced would produce 1 or 2 sparks then stop!

Steve

[soe8m]

A plug in free air on the camcover needs 2,5KV to be able to spark between the electrodes. A Mixture under pressure needs around 20Kv to be able to spark. A rich mixture when cold or a lean mixture can go around 30.000Volts needed to create a spark. LPG can be around 35Kv when not adjusted properly.

So a few sparkling plugs on the camcover do say nothing, but absolutely nothing about the state of the ignition components only that the dizzy is turning and the point do open and close and that your leads and rotor can handle 2,5Kvolt.

Jeroen

[xvivalve]

The ballast is currently attached to the coil...

In a PM, MigWeilder has ‘fessed he wound the carbs by about 5 turns to get it running on the jelly that is in the tank when I wasn’t there once. As I’m now trying to start it with fresh fuel from separate supply on full choke...

A couple of pointers for me to try whilst fitting the new points and condenser that I’ve had in my tool box the three separate previous visits I’ve made to it, thank you. Assumption, the mother of all frustration...it’s just I don’t have many sets of OE points and condensers left and as the modern ones are shite I don’t want to ‘waste’ them...

Thanks all.

[roadster]

One trick I used on flooded vehicles was to hold the HT lead at the coil with insulated pliers about 1/4 inch away from the connection post. If the ignition is healthy you will get a strong spark able to jump that gap ( or at least 3/16 inch anyway) and this will also increase the voltage at the plug tips and usually fire the engine. It might also ignite unburnt fuel in the intake or breather system with a bang so be prepared and don't do it in an enclosed space. At the least this will confirm you have a strong spark so then you can double check that the leads are on correctly and the rotor arm is pointing at the correct distributor post at the right time. The only thing left is to make sure the air intake arrangements are letting in air and there is no foreign body in the exhaust. I should add that people with pacemakers or a weak heart should not try this.

[cleverusername]

Have you rechecked the timing? You said in your original post you couldn't see it going out but you never know. After all we know you have spark, the fuel is new and the mixture is roughly right. I mean it should fire.

[dursley92]

If you have changed from electronic back to points the timing could be anywhere.
You need to check it for a reference at least.

[Carledo]

Russ is correct, I don't know about the Maplin Ei system, but in nearly all the Accuspark/Britpart systems I have fitted, I have had to readjust the ignition timing to suit it, sometimes only by a few degrees, in one case (A Rover V8) nearly 20 degrees. Simply because the trigger wheel on the shaft doesn't necessarily have its "cam lobes" in the same place and the sensor pickup position can also be a bit out from the standard points distributor position.

Not sure this is not a red herring though, as most would RUN with the timing that bit out, just not well! Your described symptoms more match a total absence of spark at the business end of the plugs.

Steve

[soe8m]

Did you actually try new plugs?

Jeroen