Practically Classics Forum

I am having problems starting my 1975 Corona GT only when cold and its driving me nuts!

The car is a japanese import with an 18RGU twin cam 8 valve engine. It has a 40 thou rebore, 10.5:1 compression dome top pistons with fly-cuts for the valves and mild cams fitted. The head was cleaned up and the vavlves shimmed to the correct gap for the cams. It's probably only done 8000km km since the engine was built.

The carbs are dual twin-throat 40mm Solex-Mikuni (Japanese DCOE copy) which have been professionally rebuilt, jetted and tuned to the uprated engine. The filters are the K&N washable type.

The ignition system is the factory electronic setup with standard coil and ignitor.

I know it's a modified engine and it's expected to be a bit grumpy, but this is ridiculous.

Basically no matter what I try the car endlessly cranks over on the starter with hardly a cough. Eventually it will fire up reluctantly, usually after the battery has run mostly flat and I jump start it with another car. The problem seems to be getting slowly worse.

Once it has started and had a couple of minutes to warm up it will start reliably all day. It then runs beautifully with no misfiring or any other problem. But give it a day or two resting and we are back to the circus of getting it going again.

The oil is a good quality 20W/50 - correct for this engine.

The fuel is 98 octane BP and it doesn't seem to matter how fresh it is.

It does not matter whether I use the choke, no choke, pump the pedal once, three or six times. The result is the same.

Spark will jump a good 1/2 inch from the plug to the block and looks fat and yellow.

Fuel is getting to the plugs okay.

Timing is spot on, and I've also tried a few degrees either side of standard timing,

There are no vacuum leaks.

- I've had the carbs rebuilt, tuned and balanced.
- I've replaced the plugs, leads, cap and rotor. I've also tried a hotter heat range plug.
- The starter cable is new and I've fitted a more powerful gear-reduction starter from a later model. It cranks fast enough.
- The battery will happily start my MR2, so I doubt it's faulty.
- I've put a scope down each bore and everything looks clean inside.
- Using the scope again I have verified the accelerator pump is working on every throat and that the inlet valves are all opening and closing when cranked over.
- I've tried a known-working coil from my Moke. (It's got a Nissan electronic ignition system fitted.)
- Compression is an even 145psi on all four pots, measured hot.
- I've cleaned up the battery terminals and all the earths on the block. The negative terminal gets a little hot when cranking, but not anything unexpected.
- A shot of Ether down the carbs does not get it going.

I'm at my wits end with the thing. It's like something electrical closes up with the heat and works reliably thereafter until it cools down and opens up again.

My current thoughts are:

- Cam timing slipped or stick valves? But then it should run like crap when warm.
- Ignition module or the sensor in the dizzy faulty. But then why does the spark appear okay?
- Leads cross-firing. But I'd expect to see that happen once it starts too.
- The battery is simply not man enough?

My gut feel is it's ignition, but I have nothing scientific to back that up.

I'd be grateful for any suggestions on what to check or try next.

Cheers,

I am not familiar with your carbs but the symptoms sound like the wrong statrting mixture - if you try to start an SU carbed engine with a busted choke cable you get a very similar scenario.
You say choke is on, is it a simple flap type or a moveable jet? is it actually working?
You could try easy start - if the engine fires up straight away and can be kept going then I think you have a carb/mixture problem.

Wicksy wrote:I am not familiar with your carbs but the symptoms sound like the wrong statrting mixture - if you try to start an SU carbed engine with a busted choke cable you get a very similar scenario.
You say choke is on, is it a simple flap type or a moveable jet? is it actually working?
You could try easy start - if the engine fires up straight away and can be kept going then I think you have a carb/mixture problem.

That was my initial impression too - choke not working. However, he HAS used "Easy Start" (Ether) so I can't believe it's that. Normally if an engine is needing more choke, a blast of spray will make it fire a few times for sure, even if it doesn't actually start. I'd say if it doesn't even fire once, then it's not carburation - and I think that's the conclusion that Brett has come too as well.

B*ggered if I know what the fault is though, a real strange one. Can you try a Gunson colourtune plug or some other type of spark tester to see if it's sparking under compression? If you can prove this, then it's pretty much GOT to be timing?

Cheers!

What state is the battery in? I had a similar problem which went away when I replaced the battery. The conclusion I came to was that the fuel drains/evaporates from the float chamber when the car has been standing and needs a fairly long cranking to fill it up again, by which time the voltage is too low to give a decent spark at the plugs. Sometimes it would fire when I released the key, removing the load of the starter and allowing the voltage to rise.

As above, and I've got to say you having been so thorough its hard to suggest a lot,

But before checking timing I would go through the entire ignition system including using an uprated battery as you say it fires up most times off a jump.

I'd suggest this as I recently rebuilt a silly DOHC motorbike engine, you know the score, several timing marks and then count the links in the chain from one sprocket to another. The damn thing would turn over and over at a good whack but never fire, and I was sure I'd cocked it up, this was with a brand new and known good battery, sold as being for the bike. Put it on the booster and guess what, she'd fire, slightly uprated battery cured it. I've had it a couple of times before on motorbikes in that they turn over fine but don't fire, yet will go with the kickstart if they have one.

So I'd try a little more umph for starting first, then run through the ignition sytem again.

Good luck with it, its the sort of thing that can drive you demented.

Thanks for the advice so far.

The fuel pump is a boot-mounted facet electric one with the correct pressure rating for the carbs. It is working okay and filling the chambers. But I'm wondering now if it's actually flooding the cylinders and putting the fire out. Certainly it stinks of fuel sometimes after I've cranked it and when it does eventually go it spits out raw fuel for a few seconds.

The choke is not a traditional choke. It's a seperate passage in the carb that dumps in basically raw fuel and a little extra air, just like a Weber. The throttle discs do not move with the choke. This choke appreas to be working, as when it does fire up it will idle up and down based on where the choke cable is set.

As Luxo said, I've tried Ether (marketed here as "Start Ya Barstard") and it either coughs once or nothing.

I don't have a Colourtune, I used to borrow a mate's but he moved to Sydney a few months ago. Maybe I should buy one of my own.

The battery on this car has different sized posts and is physically smaller than all my other cars with only 330 Cold Cranking Amps whether MR2's battery is 440 I think. I've tried using the MR2's battery attached to the battery clamps with mole grips. The Corona won't start with the MR2 battery. But then I stick that same battery in the MR2 and it starts instantly. Or if I mole-grip-clamp the Corona battery in the MR2, it starts.

I suppose I could change the clamps to normal ones and try again with the MR2 battery. Then if it solves the issue buy it a new battery.

Brett, can you get access to a decent mains powered battery charger with a boost start mode, and have it set up already on the boost setting the first time you try to start the car, that might discount a battery issue without having to mess about with batteries and posts.

bnicho wrote: As Luxo said, I've tried Ether (marketed here as "Start Ya Barstard") and it either coughs once or nothing.

It's marketed here as well, to the amusement of the natives. I'd be a bit wary of using it, it is rather violent and I've heard stories of it breaking compression rings, resulting in an engine becoming "addicted" to it. That said, your compression readings don't look too bad.

Try to start it with the fuel pump disconnected. this will eliminate any over pressure issues it should run for a minute or two on the fuel in the carb bowls.

Just a thought, how about you've got hydraulic tappets that are draining when the engine stands. Once you've got oil pressure they pump up and all is ok until, over a day or two, they drain again. Of course you might have solid tappets, in which case this explanation won't help, sorry.