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.
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| 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.
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| 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. |
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| 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. |
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| 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. |
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