Lumpy running with choke

[HQentity]

Hiya all! Hope everyone is getting on ok!

Just a few questions about choke really. When I run the car cold with choke, she runs quite lumpy. The best way I can describe it, is it sounds like she fires all the cylinders, then misses them all, sort of brup-brup-brup-brup, instead of a steady running idle. Pulls great and smooth, but if I'm for instance approaching a junction, she'll bounce all over the place if I'm not accelerating. Even slight choke seems to lead to this, I've tried using less and less choke but then she can't pull, theres no middle ground? Is this normal for cold running?

A few points:

Mixture seems fine (plugs are a great colour but no ideas about with choke?), carbs (SU) balanced, no major air leaks as far as I know, idles nice and smoothly when hot. As she warms up, the fast idle improves up to around 1200rpm & smooth. Its just the first 2-3 miles where I struggle a bit. Its not a big problem I'm just curious really if it's normal!

If I move the choke fast idle, is there a way to improve the running?

Many thanks!

[Henk]

Old spark leads in combination with damp weather? And therefore a spark to weak to enlight the rich mixture?

[HQentity]

I think they're ok, and if it's dry weather, she runs the same. Interesting about the weak spark though - I think I need to replace the LT leads, so maybe it's in connection with that? The HT leads are fine I think. The springs in the dizzy are being replaced tomorrow, so I might see how much that improves things with the timing too, she's always idled less than perfect anyway.

[MIG Wielder]

Hi Kyle, Couple of things to have a look-see at.
I think you have SU carbs.
If you are running Strombergs ... please ignore this.
* Are both S.U. jets lowering completely when you pull the choke cable ?
Pull the choke and see if they both drop by the same amount.
My guess is that when the carbs were removed to do the head that the operating lever dropped out of the lever connecting the rear to front carbs;
* Then, are both operating levers attached to the operating rod ? They can work loose.
While you are at it, the fast idle could usefully be reset by checking that the fast idle cams have the same gap between the cam and the adjustment screws. From memory this is 25 to 30 thou. Or about 0.5mm to 0.75mm in metric.
Come back to us if this doesn't fix it.
Cheers for now,
Tony.

[HQentity]

Hiya Tony

Many thanks for the help, I will have a look and see with Jess probably over the weekend if both jets are lowering correctly. Its just something thats always happened with the cold idling to be honest! She's been running fantastically touch wood since the work we did, and it sounds like the fast idle cams are pretty much where the should be too. The operating levers, are these for the jets again? would I be able to see that if I took the air filters off?

Oh, it is SU's by the way.

Many thanks again!!

[Jon Tilson]

You can see or feel if the jets move down when the choke is pulled with the filter in place.

If its running rough as you describe you have the choke jet dropped too much so its too rich.

Set the fast idle screws so you get 1200 rpm with the cable out enough to not move the jets down.

Or pop up here some evening in 2 weeks time and I should be well enough to sort it.

Also check the dashpot oil level as lack of oil will cause poor pick up especially when cold.

Do you have electronic ignition? Opening the plug gaps to 35 thou if so also helps cold running.

Jonners

[Karlos]

Hey Kyle, I am at K2 on Saturday between 09:30 and 11:00, I'd be happy have a look if you want a second point of view, but I have to do the ParkRun first, so it would be after 10:00.

Karl.

[HQentity]

Hiya Jon,

Thanks for the help! I have a couple of weeks off coming up soon, the plan is to have a look and see then. I wasn't using common sense, I didn't think about adjusting the choke from the engine bay haha! I will let you know how I get on.

Also, I don't have electronic ignition! I will get it at some point no doubt.

--

Hiya Karl,

Many thanks for the offer! This Saturday I will be heading off to Devon I think! I hope you are keeping well?

Hope you have a good weekend!