MGB Register Forum

Hoping to pick your brains again chaps!

I have just succeeded in getting my early rubber bumper car up and running. Have HIF carbs, 45 distributor with points (for the moment), silicon leads and NGK BP6ES plugs. Static timed at about 12 degs BTDC. Dry compression tested at 140-150 for each cylinder.

Car will now start on max choke, run rough until warm and then with no choke run better to idle at about 1000 rpm (trying to balance carbs at anything less seems problematical).

Have just removed plugs to discover, 1 and 4 showing little or no burn/sooting but 2 and 3 very black.

Since inlet ports are 1 and 2 , 3 and 4, I am confused!!!

Any suggestions welcomed, many thanks, David.

David it sounds like a carburettor problem but first check that the choke cable and mechanism returns fully when pushed in (not so easy with HIF's as you can't see the jet dropping and rising.
If you remove the dashpots check that both jets are the same distance below the bridge. You could turn each adjuster anti clockwise until the jets are level with the bridge and then clockwise 2 1/2 turns on each and start from there.
My SU workshop manual states a 1.6mm free movement in the cable before it moves the choke cams and make sure the latter move simultaneously when the choke is operated.
Pull out the choke until the linkage is about to move the jet then adjust the fast idle screws to give the correct fast idle speed.
The valves (if fitted) in the throttle discs can stick open. It's easy to fit plain discs remembering they are asymmetric.
. Vic Butler.

Hi Vic,
Thanks for your response and I see where you are coming from with the choke suggestion, I will check to make sure cable fully closes mechanism.

The reason I’m confused is that surely the choke in each of the 2 carbs services 2 cylinders each, but I am only getting excessive carbon on 1 cylinder in each pair! Could it be something to do with the functionality and positioning of the choke within each carb that favours cylinders 3 and 4 I wonder, especially as I don’t understand exactly how the chokes work in HIF carbs!

Cheers, David.

Afternoon David.
Cylinders 2 & 3 can run richer than 1 & 4 due to the siamesed inlet ports but shouldn't be excessive.
The HIF choke operation is an unusual system but I am currently enjoying a pint in my local so when I get home I'll look it up. However the principle is identical to the HS choke that the mixture is richened for starting but done differently so the same rules apply.
. Vic

Hi David,
I'm not sure if you have run the car out on the road for a while & then looked at the individual plugs to compare the relative rich/lean mix between cylinders. As Vic says , the engine is known to have a tendency to be richer on no2 & no 3. This can dissappear to varying degrees at higher rev levels experienced during a drive rather than not moving in a garage or static outside your house.
After a long run my standard engine , shows all 4 plugs to be virtually identical in colour,but i sense that if a short trip round the block, then 2 & 3 marginally darker.
Cheers, Charles

That sounds quite reassuring Charles! I have had the car for 9 months, previous owner delivered it to me and I’ve never driven it. Planning to take it out next week, if it ever stops raining, and will check plug condition before and after run.
Thanks David.

Afternoon David.
The enrichment device on HIF carburettors is not the standard jet dropper or flap (strangler) as on the Solex on the Land Rover so I don't really know how it works except I reckon it bleeds in extra fuel when the choke is pulled out. It's called a starter device. I ditched HIF4's in favour of genuine BL.Special Tuning HS6's and manifold back in 1981.
The principle is the same and the chokes must be synchronized like the throttle before any attempt at balancing the carburettors is carried out.
. Vic

David,
I presume you have checked valve tappet clearances as this should be done before fine tuning operation of carbs ( i am assuming you have already replaced / reset / cleaned points /plugs ) as carbs are the last things to set up?
Cheers,Charles

Hi Charles,
Yes, new points, condenser, rotor, cap, leads and plugs.
Carbs cleaned, float valves replaced and new jets in place.
Tappet clearances checked.
Cheers, David

David, did you remove the starter devices from the carburettors? There is a certain way they have to be fitted.
Did you get your points etc from the Distributor Doctor?
. Vic