1700 crossflow Intermitently running on 3 cylinders!!

[JT71]

Hi, i'm 2 weeks into Caterham ownership and having fixed a faulty headlight Yesterday (turned out to be the switch thankfully), on a 100 mile run down to the west country this weekend, an hour into the journey the car started running on 3 cylinders, very lumpy and loss of power. One of the plugs was shot so replaced all 4 plugs, no difference. Then on way back to surrey this evening, limpimg alomg at 60mph, the car suddenly regained power and started running on 4 cylinders again! Its a 1700 crossflow with twin webers.

I'm really confused as to what this can be, does anyone have any ideas where i can start? The confusing thing is that one of the plugs was completely burnt out but didn't make any difference when i changed it.

Cheers!

[Clousta]

When I got my crossflow it had been SORN'ed for 3 years. I had some misfiring and changed out the obvious culprits but the misfire hesitancy remained until after the winter where regular use had brought the car back on song.

So I think the message is to keep using it as well as changing out bits on the ignition system.

We have got so used to 21st century motoring that we have forgotten that older engines are a labour of love

[Alistair1537]

Change the plug leads.

[Sam_68]

Alistair1537 said:

Change the plug leads.

It's either ignition or fueling related.

If it's just one cylinder that's dropping out it means that it's something 'downstream' of the rotor arm on the distributor and you've already changed the plugs, so change the plug leads and distributor cap.

If that doesn't work, then it's fuelling. Again on the basis that just one cylinder is dropping out, it suggests just one choke (I'm assuming you have twin Webers?) is affected... so a jet blocked with crap would be favourite.

May also be worth checking your valve clearances and compression, but I doubt these will be the primary cause.

When you say one of the plugs was 'shot', what do you mean? The condition of that plug could be telling you what your problem is.

[buzzer]

take the tops off the carbs, only a few screws. look inside and see if there is any water in the fuel, it will be in the bottom of the float chamber if there is any. also look for any crud in there. Soak up the excess petrol with a rag. then take out the main and idle jets and give them a blow through, but importantly blow down the holes where they screw into with some compressed air. Cover with a cloth when you do this and mind your eyes!

I have had a few where water/debris in the carbs have caused them to drop on and off cylinders.

When its running OK again, spray some WD40 on the joints between the carbs and manifold with it ticking over. if the engine note changes even slightly, you have an air leak, another common problem.

[Irish]

buzzer said:

take the tops off the carbs, only a few screws. look inside and see if there is any water in the fuel, it will be in the bottom of the float chamber if there is any. also look for any crud in there. Soak up the excess petrol with a rag. then take out the main and idle jets and give them a blow through, but importantly blow down the holes where they screw into with some compressed air. Cover with a cloth when you do this and mind your eyes!

I have had a few where water/debris in the carbs have caused them to drop on and off cylinders.

When its running OK again, spray some WD40 on the joints between the carbs and manifold with it ticking over. if the engine note changes even slightly, you have an air leak, another common problem.

I had the same with my Crossflow when I got it. It would chugg under load, not accelerate and eventually cut out. Traced it to the absense of a breather pipe on the fuel tank. No funny when stopped on the M25!! After a few minutes it would be fine again.

[DVandrews]

Check for a loose choke on one of the carbs..

Dave