+2S spluttering engine issues

[mbell]

Major thing is to identify if you need a 1.5 ohm or 3 ohm. 3 ohm is standard, but later cars got a ballast resistor setup for easier starting and they need a 1.5 ohm coil.

Need to check the wiring to see if there is a ballast resistor and multiple supplies to the coil. As well as check current coil.

[leedsj]

Major thing is to identify if you need a 1.5 ohm or 3 ohm. 3 ohm is standard, but later cars got a ballast resistor setup for easier starting and they need a 1.5 ohm coil.

Need to check the wiring to see if there is a ballast resistor and multiple supplies to the coil. As well as check current coil.

It's one of the very last JPS from 1974, so I suspect 1.5ohm - but I'll get it out first to check.

[mbell]

Yeah it should be 1.5ohm but that doesn't mean it not be changed at some point or someone fitted the 3ohm by mistake. I'd take careful look at wiring/resistor etc to confirm which it should be.

[leedsj]

I'd take careful look at wiring/resistor etc to confirm which it should be.

Alas, I would have no idea what to look for / at.

[alaric]

Hi.

My car is a '73 +2S 130/5, so should have the same ignition set up as yours. It had a resistor in series with the positive feed to the primary of the coil, and another wire that went directly from the ignition switch to the same connector on the coil. The idea is that the wire that's not going through the resistor bypasses the resistor while you are cranking the engine, and that gives you a higher voltage on the coil than you would otherwise have, and boosts the spark. Once you've started the engine and turned off the starter motor the supply to the coil from the ignition key is removed and the coil gives a healthy spark from the supply through the resistor, which is around 9V across the coil instead of 12V.

Modern systems, as far as I am aware, do not use a ballast resistor, but the coils are designed to have 12V across them permanently.

So, if you fit a 12V coil, which will have a resistance of around 3 ohms through the primary (between the two terminals labelled + & -), just remove the resistor and connect the + of the coil to the wire that went to the supply side of the resistor.

If you fit a 9V coil then the resistance through the primary should be about 1.5 ohms, and you don't need to change the wiring.

As you probably had no problem with the ignition, and don't want to make changes, I suggest you look for a ballasted coil with 1.5 ohm primary.

I removed my resistor and put in a 12V coil. I connected both supply wires - the one that went to the positive side of the resistor and the one that went directly to the coil, to the coil. It works fine. I have big fat sparks on all plugs.

I hope that helps. I bought my coil from Amazon. There's a 1.5 ohm version of the one that I fitted - although the name did put me off a bit. I'll put the amazon link below.

I believe there's an explanation and circuits in Des Hammil's book on ignition systems, which I'd be happy to take a pic of and post for you - I think it's ok to take a copy of a page from a book and post it - I don't want to upset Des though.

Regards.

Sean.

https://www.amazon.co.uk/PerTronix-4001 ... 9822686691

[leedsj]

Thanks Sean, that is the best description of what is going on - much appreciated.

And yes, that is a TERRIBLY named component

[leedsj]

Sadly the new coil has not solved it.

Again, fine for 10minutes then the power drops and backfires start upon revving to the extent needed not to stall.

The voltage across from coil from the ballast resistor is only 5.6v (instead of 9v) but 12v outside of that so I'm going to try replacing the ballast resistor next.

Perhaps the engine is being starved of fuel? A friend suggested I try changing the fuel filter.. but I cannot for the life of me find it in the fuel line, only this round metal box... is that it?

[gjz30075]

That looks like an aftermarket fuel pump. Hard to tell in the picture but it is located on the back half
of the side of the block. An OEM pump has a micro screen to act as the filter, along with little screens
at the inlet ports of the carbs (on Webers anyway).

The pump is a bugger to R&R in the car but with the carbs off, it's a bit easier.

[alanr]

Sorry to hear you are still having problems.
Diagnosis of an intermittent problem via a forum is virtually impossible and you sound to me to be not that mechanically minded so your best bet I believe would be to transport the car to your nearest classic Lotus specialist.
Just changing components ad hoc and willy nilly is never going to solve your problem!

My guess from your description of the problem though would be that the problem is fuel related and I suspect a dirt build up in the fuel tank being sucked through the main fuel line and fuel pump to the carburettors. Sometimes the carburettors are starved of fuel and you get the 'spluttering' you are experiencing and sometimes you do not.
If my guess is correct, and to emphasise it is just an experienced guess, the fuel system needs a full clean out, tank to fuel pump to carburettors.

My advice to you though would be to let someone with more experience than yourself take a look at the car.

Good luck.

Alan

[leedsj]

Sorry to hear you are still having problems.
My advice to you though would be to let someone with more experience than yourself take a look at the car.
Alan

I'm feeling quite embarrassed by my lack of mechanical skill, and would like to solve simpler problems (which i am now occasionally managing). I also usually drive the 50miles to GDST in Newmarket, but in this instance it would not get that far.

The lovely thing about the forum however is help trying the obvious things / boosting knowledge but knowing when the right time to quit and pass over is.

[richardcox_lotus]

I think Alan is right if you don’t have much experience with them. But you are in Norwich so you are surrounded by experts.. pop along to the next Lotus meet up ( Look up Club lotus) to find out where and when they meet.

Also, if you feel a bit more confident, run the car until it splutters/ stops. Don’t crank it. Remove the carburettor fuel bowl covers and check your fuel levels. If the levels are low, then that will give you a clue that it’s fuel, not electrics.

This link may help:

https://lotuselan.net/forums/viewtopic.php?f=40&t=39178

Good luck and please report back, we’re always interested!

Regards
Richard

[Foxie]

What heat range are the spark plugs? (Have you the plug model number?)

What carbs do you have? Have you checked fuel pressure/flow?

Spark plugs are NGK BPR6ES (same I always use). Where / how can I check the fuel pressure?

Demon Tweeks have a 0 to 1 bar pressure gauge for £20. A Malpassi filter/ pressure regulator allows the pressure to be adjusted. A temporary fitting of the PG is all that's needed.

[nmauduit]

What heat range are the spark plugs? (Have you the plug model number?)

What carbs do you have? Have you checked fuel pressure/flow?

Spark plugs are NGK BPR6ES (same I always use). Where / how can I check the fuel pressure?

Demon Tweeks have a 0 to 1 bar pressure gauge for £20. A Malpassi filter/ pressure regulator allows the pressure to be adjusted. A temporary fitting of the PG is all that's needed.

fwiw as temporary fitting, I've drilled and tapped the cover of a Weber filter gaze



https://lotuselan.net/forums/viewtopic.php?f=40&t=46956&p=338567&hilit=fuel#p338567

[Foxie]

Now, why didn't I think of that !

[leedsj]

Am about to embark on changing the fuel filter(!)
I have not done this before so any tips before I attempt to take the carbs off?