Lumpy tick over.

[JCS]

Cass

You will find it a great advantage to couple up a temporary fuel feed to the carbs before fitting them to the engine, and applying pump pressure. The weak links are the four sealing points at the end of the fuel feed alloy link from the front carburetter to the choke assembly. If any of those four seals leak you will need to remove both carburetters again, so it is worthwhile ensuring you have no leaks. It is possible you may find these joints troublesome to cure as the limitations are the alloy threads in the castings.

Unfortunately the float chamber banjo fittings have some limitations of their own and tend to unscrew, it is therefore good practice to drill the banjo bolt heads to accept locking wire.

Did you manage to get the banjo bolt withdrawn that connects the alloy link to the choke unit, or was it seized on the threads?

Although your kit will have been labelled for HD6 units to some extent it will be generic. Generally the carb build spec on a S type will be AUD154, even though that was originally listed by S.U for use with oil bath air cleaners only. They listed four carb build specs for S Types viz AUD 109, AUD 243, AUD 153 and AUD154, also some 14 build specs for 3.8 ltr XK engines alone from 1960 to 1967 nearly all with HD6 carbs. These changes invariably lead to excess supply of odd parts in kits, although it is always wise to check if items have been missed off.

You will find the build spec for an AUD154R, (rear carb) excludes a float chamber tickler pin. The best advice anyone could give you is to either convert, or replace the rear carb float chamber lid to incorporate a tickler pin. Ensure the pin is cut off to size to stop a foul with the rising float. When combined with the front carb that should have a pin this ensures easy testing for the presents of fuel in each chamber, and the ability to flood both float chambers especially for low temperature cold starts. If you order a new chamber lid, beware they are handed and the rear one is the rarer.

I can understand why Burlen do not include needles in their kits as the variations are enormous, in addition many users alter needles to try to cope, in their view, with modern conditions. I use TM needles for instance.

I notice that you have presumably taken off, and intending replacing the carbs as a unit together. I find it much easier to remove the rear carb first, and replace it last, rather than struggle with both carbs together. In addition I use bar turned bronze exhaust nuts on the carb flange studs. These nuts are slightly longer than the original ones, but easy to remove and replace.

Best of luck with your replacement and keep us informed.

Norman

[Glyn Ruck]

Nice job! I have recently fitted new kits to my carbs due to a fueling issue. I think they don't include needles because the S Type uses TL's whereas other HD6 users use different needles. But the damn costs ramp up quickly.

SU Carb Diagram.jpg (37.46 KiB) Viewed 3651 times

[cass3958]

Thanks for all the advice guys. Got the carbs back on as a pair and set them all up. No leaks first time around. Fired the engine up and still no combustion on 1. Changed the rotor arm then the dizzy cap and the same result so it is definitely not electric. The carbs are running really well and the suction on both is 100% better than it was before and if I cover either carb with my hand the engine tries to die so both carbs are running well and balanced. Not a carb problem.
The garage I have booked the car in to to have the tappets done is a Jaguar and Aston Martin specialised so I decided to give them a call for some technical advice.After explaining what was wrong and what I had done to try and resolve it the guy scratched his head and said I had basically done everything they would have done. The only thing he could think of and is my thought as well is that the valve clearance on one is not allowing the valve to open to allow the air/fuel mixture in on tickover as the cylinder does fire up when the revs are increased.
So the car is going in on the 23rd for the tappets to be re-shimmed and we will see if this sorts it out. If not they will do some more tests but I can see this is going to cost me. If they can diagnose the problem I can fix it I just need to know what is going on here.

[cass3958]

So the car went in on Wednesday for the tappet shims to be adjusted. Got a phone call today asking me to pop in to speak to them. Sounded ominous and expensive.
Called in at the garage and they have not even started the shims yet but I had said I wanted the car back for the weekend as I have a big wedding fayre on Sunday.
What they had done though was worked out why the car was running lumpy and not firing on cylinder one. Nothing to do with electrics or carberation! No transpires the problem is to do with the Vacuum system for the brakes !!!!!!!!!!!! Yep you read it right the Brakes.

The vacuum take off is on the inlet manifold by cylinder number one. I seem to have a leak somewhere in the system which is allowing more air in to cylinder one than fuel and although I have a spark the air mixture is so weak it will not combust. They disconnected the line from the reservoir tank and plumbed it direct via the T piece to the brake servo and hey ho smooth running engine. They did not have time to go further as I wanted the car back so I will have a look myself tomorrow. Could be a leak in the reservoir tank or the non return valve is knackered so the tank is not holding a vacuum. I have noticed that my scuttle used to open straight away but also used to close straight away when I switched the engine off but now they have bypassed the brake reservoir tank it stays open for a lot longer when I switch off.
I will get out there tomorrow with my vacuum tester and check the system out.
Got to book the car back in next week for the shims to be done.

[Glyn Ruck]

Argh! something as simple as a vacuum leak. We always go chasing the complicated things first. Pleased for your sake that it's diagnosed & minor Rob.

I'm a little surprised it did not affect the adjacent cylinder as well on the B Type head but we live & learn. It does seem that you hand more than one thing wrong initially so cleaning up the ignition system etc. has not been in vain.

My car has just sprung a minor diff oil leak. Not as yet diagnosed from where. Was properly rebuilt with correct mesh & pinion bearing preload & new seals. Dead quiet. Hope it's not a sideshaft seal. Pinion seal can be done in situ.

2% seal swell additive addition to the oil will be my first attempt to fix.

[cass3958]

Initially I did have a problem with one and two but once I had sorted the electrics and re-tuned the carbs it isolated just to number one. Weather here today is a real storm and tomorrow I am busy working so it will have to be Monday before I get around to chasing the leak.

[johngosnell]

I know it is a bit off topic but many years ago a rover that I had would play up , miss fire go very lumpy and I spent a fortune trying to get it fixed and after replacing the dizzy I found that the rotor arm on the old dizzy had a loose pick up which caused the misfire after the car was driven a while after heating up.


So Pleased the problem has been located, it shows how hard these issues can be


Regards John

1B1257BW

[jonesdl]

Blimey Rob I would never have thought of a vacuum leak would cause the tick over problem, an interesting post to remember. It will be of interest to see if your tappet clearances are out also when they are done.
Cheers
Dave J.

[cass3958]

Dave my valve clearances at the moment are 10 on the inlet and 12 on the exhaust across all six cylinders which I think are too big so the car is going back in next week hopefully to have them re shimmed to being closer to factory settings which are 4 on inlet and 6 on exhaust.

[cass3958]

Got the car back yesterday from the garage after they had sorted out the valve clearances. So much quieter. I had measured the clearances at 10 and 12 but when they checked it properly one of the exhaust valves was at 16 thou. All adjusted back to 4 and 6 as factory and it is so quiet that I can stand at the side of the car and hear the exhaust noise over the top of the engine noise. Problem is the exhaust noise is half way along the car so a slight leak on one of the joints I fear I am going to have to seal up.
Vacuum all sorted. No leaks that I could find in the tanks but I did find a kink in the one of the pipes by the vacuum tank which could have been the cause. This has been changed and it runs really smooth on tick over now.