Hi all William here from New Zealand for the past couple of weeks I’ve been trying to get my xj-12 running smooth but can’t seem to a couple of weeks ago I got the tank’s relined cleaned out and did a repair kit on all the carburetors was hoping this would cure my lumpy idle but it didn’t just cause more problems I now have overflowing storngbergs but happens at random also I’ve checked the float levels and the floats replaced the needle and seats with new ones but ended up installing the old ones has it stopped the overflowing for a day but now has come back I’m waiting on a fuel pressure regulator hoping that’ll be the problem but my other issue is the rough lumpy idle can’t seem to figure it out I’ve tried to tune the carbs set the time in at 10° check for vacuum leaks couldn’t find anything all carbs are balanced emission stuff has been all removed too please any help will be a big help thanks
Hi William,
Either your float chamber needle valves are not closing properly ot your floats are not working properly, or the forks closing the valves are bent or stuck somehow.
It is a really simple system, but some new repro floats are too heavy and I have also myself once screwed up the mechanism in one of the four carbs. Once all is as should, no fuel should be flowing from the jet.
Cheers!
While high fuel pressure may flood the carbs, William; a prime reason is leaking needle valves. Have you checked needle valves and float levels? And have you actually measured fuel pressure?
Normally there are no fuel pressure regulators on carbed engines, but the fuel pressure is sometimes adjustable at the pump(s). Main point is that the needle valves close fuel supply to carbs at the properly adjusted float level…
If all carbs are flooding; it is unusual, but any carb flooding is reason enough for uneven idle - though of course not an only reason. Have you run a compression test to verify that that is not a cause…?
And welcome aboard!
Frank
xj6 85 Sov Europe (UK/NZ)
Why there thanks for the reply I’ve checked forks and measured and readjusted the floats countless times but still leaks but when I say leaks it leaks sometimes so not consistent of measured all floats to 17 to 16 mm
I’ve also done that compression test all compression is even at 120 psi Ivan store new needle and seat valves and re-measure them to make sure they’re at the correct height as for the floats they are the same ones that work previously on the car I didn’t have this problem until I clean the fuel tanks out thanks for you help
Any one in Auckland too that can help thanks
Did you “upgrade” your fuel pump? If so, what did you install?
Is it the same carb that leaks all the time ? If so I would suspect of the needle valve. If it happens in all, the reason is probably another one.
I renewed two cabs in a e-type S3 and one of the new needle valve was getting stuck systematically after, say a month-long stop. I managed to replace the valve without removing the carburetors but just the bowl, with some patience and improvised tools to reach the back screws.
Also check that you get the right needle valves, marked 2.0. I discovered the PO can installed 2.25 needle valve the reason why the A bank was running rich and i could not set the mixture right .
Let us know how it goes, best luck !
Rui
As I think you are talking about a series 1 XJ12 please bear in mind that fuel pressure is set by the regulator (just a ball and spring arrangement but it works) in the return to tank line. Also bear in mind that the return to tank solenoid valve is normally closed - so if it is not opened electrically the fuel pump is trying to pump to a dead end and may well exceed what the needle valves in the carbs can hold back.
Just a few more things to check 
Good luck,
Mike Badger
1973 DDS S1
Hi William, have you spoken with Jeremy at Jaguar Workshop in Mauku?
Hi there I didn’t upgrade the pump the same pump I’ve always been using it’s a facet gold flo pump
Hi there not the same card all the time happens to all the carbs at random I’ve installed the old needle and seat valves as my new ones leaked even worse thanks
Hi there thanks for that I will take the solenoids out tonight to give them a clean I do have a problem with them because sometimes I’ll drain into the opposite tank but I also get leaky fuel from the carburetors even if I disconnect the return line and have it draining in a bottle thanks
Cleaning the tanks should of course cause no problems in itself, Sadjag. As you have replaced the needle valves; as Rui implies - ‘new’ does not guarantee that they work as they should.
And you should really check fuel pressure at the carbs. The needle valves, float levels properly set, should close even with highest carb pump pressure, but excessive fuel pressure is ‘not good’
anyway - 6 psi is considered ample…
There is no way the engine will behave as it should if carb(s) flood. It’s difficult enough, without that happen intermittently, to synchronise carbs for ‘perfect behaviour’ at the best of times - and especially on a V12…
Frank
xj6 85 Sov Europe (UK/NZ)
I believe the nominal delivery pressure of the double ended SU fuel pumps originally fitted was 3 PSI, and I think the FACET pump is probably delivering circa 6 PSI… doesn’t sound like a big deal until you consider it is double !.. So even if its not the root cause of the overflow it can’t be helping…
Best regards,
Mike Badger
1973 DDS S1
Hi there freight I did replace needle in valve with new ones and they leaked worst so I stuck the old ones back in which was fine for about a day but then they all started to leak again right now it’s only one carb leaking so I might take the float bowl of that one and just double check the Heights thanks
Yeah that’s what I was hoping I’ve bought a fuel regulator that should be here in the next couple of days so hopefully that does it thanks for your input Mike
What float needle valve did you use in the replacement? Grose ball valves don’t have a good track record when used in Zenith-Strombergs!
Do you have a means for testing the output pressure for the Facet pump? Without knowing the output pressure you’re just poking in the dark IMHO. The car didn’t have a fuel pressure regulator and shouldn’t need one now with the correct pump (output Pressure) installed.
Needle valves will seal up to a point (pressure). If the delivery pressure is too high OR the float level in mal-adjusted that can lead to such problems.
Do you have a Z-Stromberg overhaul manual? Are all four carbs having the same problem?
There is a solution, just be patent… Ha Ha
Cheers,
Dick
Indeed, Sadjag; you just have to pursue the leaking to a proper solution!
You did of course shake the float to ensure it was dry inside. You may consider increasing the clearance beyond 17 mm to increase the pressure on the needle valve - though it is hardly a ‘proper solution’. It’s imperative that the actual fuel level in the carbs are equal - or there may be carb synchronisation problems later…
Leaking means excessive fuel level, and the petrol finds its way out whatever the cause…
Frank
xj6 85 Sov Europe (UK/NZ)
Note that it is possible to buy float needle valves with filters. These keep bits of crap from the intimae of the rubber hoses from jamming the valves
Well worthwhile