Jaguar XK140 Coughing

[jjbradders]

Hi All

Restoring a 1955 Jag XK140 for a friend and have fitted triple Weber 45DCOEs in a hope to get a few more horses (plus they look amazing!)

However the rear two cylinders are coughing very frequently at idle and touching the throttle just makes the whole situation much worse. This never happened when it had twin SUs fitted. All I've seen are yellow flames around the throttle butterflies on the odd fire. I'm pretty sure it's not the cam timing as I've set this twice, plus it's only on the rear cylinders.

Can anyone diagnose this? I've fitted a new coil and have an electronic ignition set up on order, but that's more just to compliment the carbs.

Any help much appreciated
Cheers

James

[jjbradders]

Well that wasn't an option in the kits! Apparently they work well but I could be wrong. The main reason they were swapped because the old SUs were too worn (the car hasn't run since 1992, does now but badly)

I've had another fettle with the ignition timing and it's running a lot better so I think I'm getting somewhere.

Cheers

James

[jjbradders]

Thanks for the help guys, tried everything you said and it now runs a hell of a lot better.

Still spitting slightly but at least it revs properly AND runs on 6 now!

Car looks fantastic! Sadly I'm the wrong side of the voting age so haven't been around long enough to identify cars from their engine bays, so what is it? Looks E-Type esque?

Cheers
James

[jjbradders]

XKSS?

About a year ago I was taken for a spin in a replica XKSS that looked extremely similar at the NEC?

[jjbradders]

Sounds like a decent trip that.

I'm trying to cobble together a 1979 Fiat X1/9 for myself, which is my start in the classic car world! This Jag is the first time I've ever worked on carbs actually so it's a learning curve...

Sadly the Fiat doesn't look quite as majestic as your replica lowdrag!

That was from a few moths back but not much has changed!

[jjbradders]

Pretty small section actually, the rear webers fit fine without modification and I only had to cut the area to fit the trumpets. Does however mean the front carb must be mostly disassembled to fit it in.

It's a LHD roadster that was converted to RHD in the early 90s. From what I know: imported 1990, driven until 1992 then garaged ever since.




I'll try and get more pictures soon.

[jjbradders]

Well the coughing has pretty much gone!

Sadly it now struggles to rev, just dies down if you open the throttle quickish and only revs if you gently open the throttles. Any more ideas?

Cheers

James

[jjbradders]

That's fantastic information John, thanks!

The carbs are all new and allegedly came jetted suitable for the Jag, just to get it to a rolling road. I imagine that it's the dizzy potentially screwing things over. I have to retard the timing to start it then advance again to run, which would be problematic for normal driving to say the least.

I'm going to fit one of these 123 electronic ignition distributors instead but I'm waiting on that.

Has anyone actually driven an XK, and what are the things to watch out for?

Cheers

James

[jjbradders]

Well there's no vacuum at all just for the time being as I'm swapping distributors, so that's probably why. My Fiat doesn't have a vacuum advance though, so I'm not sure what the benefit is? IIRC it's about engine load?

Talking about vacuum, what are the typical symptoms of a vacuum leak? I only ask because I'm not 100% sure of the manifold to head seal.

That's a great diagram thanks, I'll have a look when I run it tomorrow.

Thanks for all the help again

James

[jjbradders]

Well she's running a charm now! (The car that is...)

The mains are a little lean so I'll get the next size up. But thanks for all the input so far!

So now the electrical faults have started: The petrol gauge won't turn off with the ignition switch and it keeps flicking between full and empty. The ignition switch also occasionally doesn't cut power to the car after the engine has been running for a bit. Do these sounds like grounding issues?

Thanks again

[jjbradders]

uk66fastback said:

Yes, earthing problems usually ... you'll have to get the wotsit out and go through it all ...

Ah yes, the good ol' Wotsit...

[jjbradders]

Well I'll try the flush idea. Also going to fit larger mains and pump jets too, just because it feels like it's leaning out.

Finally took a few decent pictures after giving it a wash and brush up.



Sadly the Jag isn't here anymore due to the joys of A levels, so I'm getting it back in July to work on. In the mean time, I have a Fiat X1/9 to spray, so that'll keep me busy

[jjbradders]