1700 crossflow starting problems

[voodochilli]

Hi all
I have a 1994 Caterham 1700 crossflow with webber 40s which starts, runs for a few seconds then coughs and dies. I have removed the fuel ilne from the carbs and there is a good flow. I have a bosch coil and a dizzy fitted with pertronix ignitor. I have attached a spare plug to one of the HT leads and am suspicious the spark is below par (yellow not blue) new plugs and gaps cheched - no improvement! The dizzy is a pig to work on as the webbers are in the way.
I took it for a run the day before the MOT and purred along... more like a growl really with my exhaust. went to go for the MOT ...fired up... coughed a bit pumped loud peddle... coughed a bit longer and died. restarts immediatly but same routine. all exhaust pipes heating up so some combustion.
Any ideas please

[Skyedriver]

Dizzy rotated due to loose clamp?
Blocked jet in carbs? Unlikely.
Blocked filter in both carbs? Unlikely
Water in the fuel from a dodgy fill up?
The ignition thing you have has failed?
Leads swopped over by mistake?
Rotor arm or dizzy cap damaged?

Coils usually fail when hot IME.

[voodochilli]

Thanks Skyedriver, I have checked most of them, the peronix igniter website says it either works or it doesn't, no half measures.

[BertBert]

What happens after it coughs and dies? How long until it starts up again?

[voodochilli]

Hi
It restarts immediately, and goes through the same routine. The fuel pump is still ticking over so it doesn't sound like the fuel line is needing to repressurise.

[BertBert]

Sounds so much like a fuelling issue to me! Does it last a shorter time with more revs when it starts, if that's possible to tell?

Not sure I recommend this, but can you spray easy-start in to create an additional "fuel" supply to see if it lasts longer? I mean a spray in before trying to start, not a continuous spray as it's starting as it were. The latter can turn out very badly.

I've done this to diagnose a weber problem on a 911.

Bert

[voodochilli]

Thanks Bert. I thought fuel but there is good flow at the carbs and I checked the filter pots as soon as it cut out and there is fuel evident.
I have tested the pertronix igniter today and it didn't look good so I have ordered a Powerspark unit to replace it. A pig to change as the carbs are in the way but process of elimination. Coil resistance is within spec so hopefully that is ok.
Cheers

[BertBert]

voodochilli said:

Thanks Bert. I thought fuel but there is good flow at the carbs and I checked the filter pots as soon as it cut out and there is fuel evident.
I have tested the pertronix igniter today and it didn't look good so I have ordered a Powerspark unit to replace it. A pig to change as the carbs are in the way but process of elimination. Coil resistance is within spec so hopefully that is ok.
Cheers

Well that should eliminate it certainly. Good luck and let us know what you find!

[voodochilli]

Well, fitted the powerspark and I have a spark. A couple of issues but it is in.
Unfortunately its still not running. Won't start at all now. Tries to fire but won't catch. 🤪
No idea where to go now.

[Mabbs9]

I had a similar problem a long time ago. For me it was a loose connector for the optronic ignition I think. A small plastic plug was being vibrated by the engine (1600 version of yours and lumpy at idle due to the cam).

I investigated fueling etc and then knocked the plug and it stayed running. It had a really poor contact in the connector and was immediately fixed when I played around with it.

Not a huge help I know but it seemed worth sharing.

Good luck.

[Skyedriver]

Still wonder about water in the fuel.
Or old fuel blocking a jet
Or plug leads in wrong order, (rotor arm goes anti clockwise IIRC)

[voodochilli]

Skyedriver said:

Still wonder about water in the fuel.
Or old fuel blocking a jet
Or plug leads in wrong order, (rotor arm goes anti clockwise IIRC)

Can't see how, it ran last week with the same fuel and hadn't even looked under the lid. Put it in the garage untouched aftet a good run and a couple of days later would not run.??? The fuel is premium grade and less than 6 mths old.

[PiersR]

Many years ago, I had a similar problem with my Super Sprint. In the end, it was the fuel pick-up pipe which was sucking in some tank sealant and blocking the feed to the engine. It was a tank out job. I did put an air line on the carburettor end and blow back down the line into the tank. That enabled it to start but did not cure the problem, as the sealant was still loose in the tank.

[voodochilli]

PiersR said:

Many years ago, I had a similar problem with my Super Sprint. In the end, it was the fuel pick-up pipe which was sucking in some tank sealant and blocking the feed to the engine. It was a tank out job. I did put an air line on the carburettor end and blow back down the line into the tank. That enabled it to start but did not cure the problem, as the sealant was still loose in the tank.

Thanks, my first thought was fuel starvation. I don't have an air line but took the fuel pipe off the carbs and ran some fuel into a jug. I had a good flow. Certainly enough to fill the carbs and run for more than a few seconds. Do you know another way to check?

[BertBert]

I'd be getting my can of eaystart out now to see if engine runs on this for a burst to try and binary chop the problem to fuel or spark.

Also if the problem has got worse since the change to the electronic ignition then there's quite likely a problem with that in some way.

Bert

[voodochilli]

BertBert said:

I'd be getting my can of eaystart out now to see if engine runs on this for a burst to try and binary chop the problem to fuel or spark.

Also if the problem has got worse since the change to the electronic ignition then there's quite likely a problem with that in some way.

Bert

Off to the shops for a can of easy start it is then.

[PiersR]

If you have a foot tyre pump, that can be used.

[voodochilli]

PiersR said:

If you have a foot tyre pump, that can be used.

Thanks, why didn't I think of that! I have a diaphragm pump, will a blow through still work? I tried blowing down the tube....all I got was a sore lip.

[PiersR]

Just a thought, have you checked the voltage supply to the coil , I.e. 12vdc. Make sure it’s getting a good supply. You could also check this voltage when cranking. If it is dropping to below 12vdc, then if it is, you either have a bad earth or high resistance connection.

[voodochilli]

yea success - turned out after changing the ignition module the timing was out. Played with the dizzy and she started. Off to the MOT tomorrow.

Thanks for all your help everyone.