Carburettor overflow Hif4 overflow pipe

Well... I eventually got around to changing my fuel filter.  I don't know when it was last done but this was certainly in the period of the PO. Since it looked fine and was clearly passing petrol I wasn't too worried...  A routine precautionary service... . Or so I thought!
I replaced the filter with another paper element disposable - transparent as I like to see if there is any muck collecting. I checked that the car started. .. which it did.  It was a few moments later that I became aware of a strong smell of fuel. Checking under the bonnet I was horrified to find a flood of fuel from the overflow on the rear carb! There had been no sign of this previously but a carb overhaul was clearly needed.  I removed and stripped the carbs as described previously and found badly worn, grooved needle valves in both. 

Needle valve from leaking carb- grooves obvious around sealing cone

although the front was still holding the damage on the rear meant it couldn't cope with the increased fuel pressure following the filter replacement.  More worryingly, this seems to have been a problem for some time as the float had been adjusted so that it sat well above the rim height when inverted onto the needle- let alone 1mm below! This had allowed the float to press harder on the needle and so compensate for the poor seal. However this would have been at the expense of fuel levels and I think excessively rich running is likely to have resulted. Its easy enough (and cheap enough) to change the needle valve so I don't know why this was done as anything other than a get-you-home fix.  I  fitted new viton tipped needles and valves and corrected the float height. Since I was in there I also fitted new needles (AAU) and jets and replaced the float bowl gasket and the sealing ring/washer on the jet adjuster screw and float pivot. I had previously replaced the cold start system gaskets and seals and fitted new throttle plates lacking the poppet valves. Clearly I should have stripped and serviced the carbs completely at the same time instead of changing things piecemeal like this, but I had always intended to swap in my replacement set- I just never got around to it!  Anyway I've got there in the end. The inside of the carbs was completely clean and required very little attention. Once reassembled the Carbs no longer leaked and the car ran better than before once the carbs were readjusted and balanced.

However, the flood of fuel had woken me to the fact that my car has no overflow tubes that could route spilling fuel safely away from the motor ... if spilling fuel can ever be routed safely that is?
Earlier cars, fitted with HS2 carbs, had metal overflow pipes routing the fuel flow down to the bottom of the block where they were secured in a metal clip fixed to a specially made bracket. This was essential because the overflow outlets on the HS2s would otherwise have directed the fuel directly over the hot exhaust manifold. The special bracket and clip hint at the importance associated with this system. Hif4 carbs are different and frankly, I'm not convinced that my car ever had such a system.  Firstly the BL parts catalogue shows  no such pipe for the later cars and secondly the HIF4 carb overflows point fore and aft-  parallel to, but not directly at, the block. Secondly,  although I can appreciate why a PO might have removed the pipework, it obviously does obstruct access and must become tedious,  I am less convinced that they would have bothered to remove the lower pipe clip, which in my case is also absent. Looking on the web there are several pipework arrangements suggesting that these have been derived individually rather than by following a set factory-routed solution. I found some over-the-top arrangements that link the overflows above the carbs, join and discharge through a charcoal cannister- probably only applicable in the USA. Others route the rear carb pipe behind the heat shield and around the exhaust downpipe which seems likely to vaporise any overflowing fuel.

Despite this I remain convinced that some overflow is better than none and the sight of uncontrolled leakage was enough to give me kittens,  so I set about making a system from copper brake pipe. I decided to take the outflow from the front carb parallel to the block until it cleared the heat shield horizontally, and then vertically down until it cleared the heat shield vertically. It could then travel straight back to the block before turning through 90 degrees and following the block down to the position on the lower retaining bracket. In later cars this was fitted directly to the mechanical fuel pump blanking plate  and the special bracket was discarded. The rear carb overflow was routed  through a 180 degree dog-leg to return under the carbs but in front of the heat shield to  meet  the outlet from the front carb.  Both pipes could then travel back together to meet the block and then across and down to pass through  the retaining clip and discharge below the motor.  I connected the pipe to the carb overflows using transparent fuel pipe since I want to see instantly which carb is leaking if this happens again. Finally, I tied the pipes with a cable tie in a figure of 8 to stop them chafing and supported them by passing the tie through a hole in the heat shield. This isn't taking any weight or strain, its simply acting as a steady to stop the whole lot shaking about as the motor runs. Next time I have the heat shield off I will insert a metal eyelet to protect the heat shield. To make sure I have dealt with any potential fuel leaks I also replaced the inlet fuel hose and the carb linkage hose with new 5.6mm  fuel hose J30 R9.

Front carb overflow pipe clears heat shield horizontally then angles down to clear it vertically. Note transparent ethanol resistant fuel hose  connecting to the carb itself.

Rear carb overflow passes in a dogleg under the carbs but in front of the heat shield to meet the pipe from the front carb. Note new carb link hose now fitted.

Pipes pass together back to the block and then down and across to enter the retaining clip attached to one of the bolts on the fuel pump blanking plate. Pipes extend downwards to discharge below the sump/block join. Note figure of 8 cable tie steadying the pipes and providing a spacer between them.

Hazard warnings not warning of anything

Here with my cautionary tale of how I forgot basics and spent a long time chasing a very simple fault!

Instrument light sin the MGB are poor to very poor- and as I have a fair number of LEDs left over from my Lotus conversion I decided to use these in an attempt to improve matters. I managed to swap most of them (speedo and rev counter new bulbs awaited), but during the process I became aware that the hazard warning flasher was inoperative. The steering column indicator switch was working normally or I would have noticed sooner!  However, straight away this tells me that the wiring from the bulbs to earth is obviously fine and the fault is unlikely to be serious- although something clearly is wrong.

Working on the basis that I have probably upset something with a previous job I need to investigate  past activities. I have swapped the starter (and so all its positive post connections), Ive moved the relays (I fitted a new ballast bypass system) and of course I could have dislodged any connectors behind the dash whilst I struggled with the instrument lights.

Wiring diagram for flasher circuit: Power comes in via the brown wire which originates at the starter relay where its joined to the positive post connection, power doesn't pass through the relay. The brown wire has an internal fuse (not shown) and terminates at the flasher unit. Power is then fed via a light green wire to the hazard switch. When this is operated all 4 of the top contacts are connected supplying power to both R and L flashers as well as the tell tale light in the switch... note my car doesn't have this switch, the tell tales on the dash are used to show the flashers are working and the internal bulb is connected to the panel lights via external connectors (not shown in this or and diagram I have found!).

I first checked I have power to the flasher unit. Both direction and hazard flasher relays are below the dash on the right,  in my case both were rectangular 2 pin units each served by two wires.  The hazard warning flasher has to dissipate 84 watts in use and is larger than the side flasher unit which deals with only half this power. The hazard unit  has a brown permanent live feed and a green/brown connection to pin 3 on the hazard switch.  The flasher relay receives a green brown ignition controlled live and a green feed to the column switch.

Flasher units below dash on right. The smaller (lower) box is the direction indicators and the larger box for the hazards.

I checked for 12V at the brown input lead and found it using a voltmeter.

In order to test the relay I swapped the connections from the flasher relay to the hazard warning relay making sure the power in connection was made to the correct pin. A better test would be to connect the hazards to the flasher relay but the power would probably overload it so this is second best.   The switch indicators then still worked suggesting the hazard relay is able to cope with that load at least, so I turned my attention to the switch.

Switch pulls out of dash- note 4 pins at top, 2 at the bottom. There are side terminals which connect the internal bulb to the panel lights.

The switch fits into this back plug. Note that socket for pin 3 is missing as this isnt used in my car. Also the two wires with spade connectors which connect the panel lights to the switch's internal bulbb

The switch should have 6 pin terminals, I'm numbering them 1-4 at the top and 5-6 at the bottom.  The bottom two power the direction indicators for normal driving and the top 4 are concerned with the hazard warning function. These pins connect to the loom via a rear plug which has corresponding sockets. Note that the socket for pin 3 is missing; this would normally flash the switch's internal light as a tell tale when the hazards are working. However in my car the dash tell tales are used and this pin has been disconnected, the switch's internal light now being connected to the panel light circuit.

I next tested for continuity between hazard relay green wire and socket  4 which was OK, and 12V from the relay was detected here.

The lower pair of pins (5 and 6) are simply a pass through for the ignition controlled feed from the flasher relay. These are connected for normal driving  to feed power from the flasher unit to the column direction indicator switch. When the hazard warning button is activated this power feed has to be interrupted so that the flasher units don't interfere. I tried removing these wires in case the internal switch disconnection mechanism wasn't working.  This made no difference and the continuity meter confirmed that the switch was operating correctly on these contacts.

For the hazards, when the switch is operated power in pin 4 is connected to pins 1,2 sending power to the left and right indicators to flash them simultaneously. I tested these actions with the continuity meter and as far as I can tell,  the switch functions exactly as intended. I checked that pins 1 and 2 are connected to earth (through the flasher bulbs ) and tried bridging terminal 3 to each in turn. This should provide power to the bulbs and light one pair of indicators- but the bulbs didn't light. However the 12V was no longer detectable suggesting that it was being earthed???

At this point I began to suspect that 12V input isn't always a 12V input and rigged a bypass lead directly from the battery. Connecting this to terminals 1 or 2 on the switch plug gave steady illumination in the relevant indicators which eliminated any weird shorting between the switch and the lights. Further- bridging this feed directly to  terminal B on the hazard flasher box restored full function!

12V feed direct from battery to hazard flasher unit restored function.

Obviously this throws suspicion on the power feed to the hazards- and as I have been moving the relays about I could have disturbed something. I checked all were still secure and connected properly.

Starter relay removed- all wires had good connections. The attachment strip is corroded and I cleaned it but it isn't used as an earth. The feed for the hazard flasher unit is via one of the two brown wires entering a single spade just above my thumb.

I disconnected the fly lead from the battery and reconnected it to the brown wire spade disconnected from the starter relay. The flashers still worked so power was clearly arriving at the starter relay as expected from the  fact that I can start the car. Any problem must lie between the relay and the flasher unit. This is essentially a single stretch of wire, although it does pass through a 17A  inline fuse. I removed the fuse and checked it- continuity was fine although the contacts were perhaps a little dirty. I cleaned it, refitted it and Hey Presto-  my problems were cured! I conclude that when I fiddled with the relays I must have disturbed an already poor connection worsening it to the point where although V were passed the resistance was so high that no current could actually flow when demanded.

In line fuse holder- brown wire feeding the hazard warning flasher unit

I was surprised that such a small amount of dirt could cause the problem so took  my cue from this to clean the other in line fuses. All were dirty to some extent and one (35A feed to cooling fan) had a cracked cap, although still functional. I changed all fuses and refitted them with a smear of dielectric grease which I'm hoping will prevent this problem in the future.

Gear lever bush replacement and rewiring the overdrive switch

When I got the car the gear lever looked lovely... but there were problems! Firstly the gear knob was loose and tended to rotate around the gear stick. Not surprisingly this strained the wiring to the overdrive switch which in my car is mounted in the gear knob, leading to an intermittent fault. Secondly, when I removed the gaiter to address this issue, I discovered a litany of past bodges and half a sofa in terms of foam wrapped around the gear lever- presumably to control vibration and noise. I did make a temporary fix so that the overdrive worked again but in the longer term it was clear that I will need to rewire the switch and also replace the nylon bush at the base of the gear lever which can cause vibration when its worn and may well have been responsible for all the past troubles. 

The overdrive switch simply pops out of the gear lever by twisting a screwdriver in the front slot

Gear lever and gaiter secured by 4 cross head screws.

Gaiter ring screws. One of these is smaller than the others and this fits at the front of the ring.

Lifting up the ring reveals the foam padding I had found previously

The conical ring below the knob is screwed down away from the gear knob

The overdrive switch just slips off the two contacts beneath so you can look inside the knob...

... and the slotted ring inside the knob is removed by unscrewing using a fine screwdriver to push it round.

Then the knob can be removed revealing my previous packing! (which I now remove)

The gaiter then lifts off revealing...

.. the mass of insulating tape and chocbox junction points left over from previous bodges.

The  console will then come off but you have to remove this screw at the back of the console tray

Console removed.

... and bad wiring assembly separated from the gear lever- its chaos with lumpy dodgy contacts. The yellow wire passes through 2 choc box junctions and three wire colours before joining the switch!

Although its probably not absolutely necessary, I removed the under tray by removing the three short cross head screws and their spring washers from the front.

Removing the lower plate...

...opens up access. The gear lever is held on by three special (shouldered) bolts passing through special (Thackery) spring washers and securing the horseshoe mounting ring (slot faces forwards).

Removing the three bolts- take great care not to drop them or their washers

I didn't want the wires to disappear down the hole either so I held them with string.

Horse-shoe plate removed..

... and the gear lever then lifts out- it should bring the old nylon bush (this one red) with it

The socket needs cleaning up- just visible inside is the small brass rod that acts to take up any clearance as an anti rattle system (about 2 O'clock). Just visible at 12 O'clock is the guide pin that prevents the gear lever from rotating in the socket. The brass rod can be lifted out carefully,  use a magnet to fish out the spring behind if it doesn't come out inside the rod. Give everything a good clean

Anti rattle brass rod and spring... not clear here but the brass rod had a sharp burred edge and has clearly distorted in use. There wasn't a lot of  grease in the housing. I removed the burring with a file to let it slide more easily over the gear lever ball. Pack the rod with grease and insert the spring.

The gear lever components separated.

Cleaned up socket and all fixings.

It was then time to sort out the overdrive switch. I decided to replace all the cobbled together sections with new flexible silicone wire. This has to fit within the gear lever slot so I first tested that the wires were not too thick.

Testing the new wires for fit in the lever groove.

The problem is that the overdrive switch has unusual connectors. They look like round pin connectors (or possibly female bullets) that are being misused in the this application! They connect not to a pin, but to a thin plate which slips into the seam slot of the contacts. However the main problem I have is that I don't have any more of these contacts and so had to use the originals again. Last time I had joined them by soldering them onto fresh wire, but the soldered section is stiff and cumbersome. It doesnt fit easily into the gear knob and rather undermines the purpose of using flexible thinner wire. I was forced to carefully uncrimp the terminals from their old wires and connect them to the new with a combination of crimping and soldering. I fitted bullet connectors to the other ends of the new wires to replace the various choc-box junctions.

Round pin connectors? Slots visible that grip onto the plate contacts in the overdrive switch.

I polished up the ball sections of the gear lever on the brass wheel before greasing them and fitting the new nylon bush- more grease on the outside of that.

Greased lever, new bush on end.

Do not forget to replace the brass rod and its spring in the side of the socket. Then you can align the slot in the lever ball with the socket guide pin and the lever then pushes downwards into the socket. Its a bit of a springy contact and is held down against this springy-ness by the horseshoe plate so you need to refit this with its thee bolts and washers. You can then refit the lower tunnel cover plate and feed the two wires through.

Horse-shoe plate and lower tunnel cover plate installed

... and connect the new using the bullets

New wires connected

Refit the console- again feeding the overdrive wires through the console, up inside the gear gaiter and through the keyway slot in the lever where they can be held with the conical ring nut. I inserted a length of tubing to take up any room left in the lever slot and allow the key inside the gear knob to grip- probably not necessary unless the gear knob is worn as in my case.

New wires fed up inside the gaiter and through the lever slot. The conical nut holds them in position., Here I am testing a piece of packing tube to take up any space in the groove keyway.

Push the gear knob down over the wires and onto the lever engaging the inner key with the slot in the lever. Refit the ring nut inside the gear knob and then screw the base cone back up against the gear knob to hold it tight. Finally, reconnect the overdrive switch contacts and clip the switch down into position.

Reconnecting the overdrive switch

Finally job done! Don't forget to reinsert the screw at the rear of the tray in the console.

Upgrading to Accuspark electronic ignition

Having  initially bought a high energy Powerspark distributor I subsequently decided not to use this and returned it.  This was because the HE system required a low resistance 12V coil and to bypass the ballast resistor system: I have just reinstated this system following the installation of the new starter so I'm not too keen on undoing this, and anyway the ballast system makes sense to me.  Secondly,  the new distributor lacked a vacuum diaphragm and consequently would look different from stock.  Instead I opted for a Stealth Accuspark conversion kit for the existing distributor which has now been cleaned and lubricated.

Stealth Accuspark kit- appx £30

As before the first step is to set the motor at tdc with no 1 cylinder on compression,  the rotor arm pointing at no 1 plug lead.

Motor at tdc

Distributor cap removed- Rotor arm pointing up and forwards at no 1 HT lead.

Remove distributor by unscrewing the two clamp to block bolts- not the distributor clamp bolt so as to maintain some semblance of correct timing.

distributor removed.

 I could then clamp the distributor in the vice (soft jaws) and start to dismantle it.

 Pull off the rotor arm revealing the points plate and condenser

 Pull the lead off the points spring and remove the clamping cheese head screw

 ... and lift the points plate off.

The coil lead passes from the points, through a grommet in the side of the distributor, but whereas earlier cars have this  grommet fitted into an open half-moon slot so it simply lifts out, in this distributor the wire passes through a hole drilled in the distributor wall. This means  you have to cut the wire to pull it through and remove the contact breaker plate.

Cut wires and pull through the grommet in the wall.

 The condenser is retained by a single screw so undo this remove the condenser but leave the earthing braid cable attached to the lower plate.

The magnetic trigger sleeve slips over the distributor shaft- it has a quatrefoil internal profile that fits closely over the spindle lobes so it cant go on wrongly.

The new pickup is fitted next, it slips over the stud that retained the contact breaker plate tip and is retained by the cheese-head CB plate screw into its original hole. The new pickup plate has a slotted location hole which allows the unit to be adjusted in its  final position. The pick up on the base plate must be close to, but not touch any part of the collar on the shaft as it rotates and although the size of the clearance gap isn't critical, it should be as even as possible.

Pick up positioned to give an even gap between collar and pickup and does not contact the sleeve at an point in its rotation. Note grommet already fitted onto the wires.

The new unit already has a grommet on the leads to insert into the distributor wall. However, the fact that this is a hole rather than an open slot means that the wires will not pass through and once again I needed to cut the terminals off to slip the wires into place. I will refit appropriate terminals later.

I had to cut these lovely new terminals off.

The earth braid has to be re-instated. Since there is now no condenser mounted beneath it, I needed to fit a spring washer on the screw to ensure it made good contact with the floor plate. Here the braid has been refitted.

The kit also comes with a cable tie to ensure that the new wires are tied away tidily and will not foul the base plate as it moves. Cut the excess tie off 

 ... and fit the rotor arm- I used a new red arm

Finally I could refit the distributor by reversal of the above process. I re-timed the motor to 30 deg full advance but you have to slacken both the distributor clamp bolt and one clamp-to block-bolt to allow the distributor to be turned.

In the event, I also installed a new Accuspark coil to ensure maximum compatibility with the new system although this was probably not absolutely necessary. In any event the coil I had was a Lucas item, possibly the original and so  now some 40 years old and replacement shouldn't hurt!