Hello all.

Due to my schedule and life getting in the way, and buying a car which has meant that riding the NC30 isn't a necessity but a choice I have not taken her out in a while. For this insult she has rewarding me with various problems.

One - leaking fuel tap. I had the fuel hose on the correct spigot from the tap, and the vacuum hose was attached to the spigot facing directly down from the tap assembly rather than the one facing to the front of the bike as suggested by the Haines manual. She has been running fine like this for months. What is the difference between the two spigots and which one should you actually use? There is a small leak of petrol dribbling down the outside of the bottom spigot which as I have had the vacuum hose attached, has leaked down into it so when i took it off the tap, the fuel pissed out of it all over me, the bike, and my drive. Is it likely to be a seal that has gone?

Two - I emptied the vacuum hose and reattached it to the fuel tap on the spigot stated in the haines manual, ignition on, fuel tap on, killswitch in run position, push the starter once and the engine half cranks then stops dead, no clicking sound from relays or anything else. Just a dead stop. It did this the other day, I left it for a minute to call a mate to see if he could come get me if I couldn't get her started, hit the button again and she started fine. Electrical problem or are the two related? HELP!

Someone please suggest a possible cause and a solution before I kick it off its stand in a fit of rage!

the pipe for the vacuum goes on the furthest to the outside spigot - not the middle one. Middle is a drain.

seems that your tap is fucked...the diaphragm is allowing the fuel to flow regardless of the vacuum.

the second problem - sould easily be a hydraulic lock - fuel is getting into the cylinders and the bike cannot compress this - instand stop - possible damage to be caused includes bent con rods..so sort the tap out!

As mark has said,
replace fuel tap
remove plugs and turn over by hand and leave to clear / fuel evaporate
change oil and filter as it will i bet be full of fuel too

As suggested, drained the tank, removed and inspected the tap, nothing looks perished in terms of the seals inside the tap mechanism but clearly something is wrong! removed all the plugs, slightly oily on threads but good condition otherwise not wet with fuel, cranked the engine over by hand and it is now laid up in the garage as suggested for the fuel to evaporate.

Have looked on Lings for spares for the fuel tap and it seems lots of the parts come as assemblies rather than individual components so basically need a working tap assembly from somewhere or someone £35 on fleabay! FFS!

Just for the record then: The spigot facing directly down is the drain but as my tap is clearly fucked anyways is didn't matter which spigot I had the vacuum tube on it because my tap was flowing fuel anyway?

if looking from the right side of the bike and assuming you just lifted the tank a bit
big one = fuel outlet
spigot / breather = short thing that should point down in the middle
vacuum = closest to you facing backwards or down and attaches to the vacuum pipe.

as for fuel tap, speak to geoff33 or post in the for sale wanted section. for new try david silver spares.

Hello all. Good news. She lives. After putting a new diaphragm assembly into the fuel tap that sorted my leak, so then just a case of whipping the plugs out and turning the engine over by hand as suggested to encourage the petrol to evaporate from the chambers and hey presto.

Given that the pistons should be completely sealed in the bores I shouldn't have any problems with the leaked fuel having got into the sump should I? If it's a possibility can someone explain how so I can get my head around it? lol. Also got an 56 5sl reg rec in the post as mine was kicking out 16.0v at tickover :-s She should be ready just as the weather turns shite for winter....

Fuel dilution of your oil is a real problem. Fuel will pass by the piston rings. Best course of action is to replace your oil and filter, (best to then warm the engine then replace oil and filter again, but this is personal choice as it can be very expensive!)

Ben.

votejc wrote:Hello all. Good news. She lives. After putting a new diaphragm assembly into the fuel tap that sorted my leak, so then just a case of whipping the plugs out and turning the engine over by hand as suggested to encourage the petrol to evaporate from the chambers and hey presto.

Given that the pistons should be completely sealed in the bores I shouldn't have any problems with the leaked fuel having got into the sump should I? If it's a possibility can someone explain how so I can get my head around it? lol. Also got an 56 5sl reg rec in the post as mine was kicking out 16.0v at tickover :-s She should be ready just as the weather turns shite for winter....

Of course... pistons are never 100% sealed, there sealed by loose fitting rings that take up the slack.. this is almost a perfect seal in a good engine but if you do leave fuel in the bores it will leak past the rings.

The worrying part is that your carbs let the bores fill up.

This is a sign that the carbs are leaking fuel, this shouldn't happen in a healthy carbs.

The carbs have internal floats that shut off and stop fuel flow when they are full, otherwise fuel will just keep flowing and go into the engine bored... sounds as though one or more float pins on the carbs have failed.

votejc wrote: Given that the pistons should be completely sealed in the bores I shouldn't have any problems with the leaked fuel having got into the sump should I? If it's a possibility can someone explain how so I can get my head around it?

Piston rings are not fully circular, they have a small gap to allow you to 'open' them to fit them over the piston crown. If you do a google image search you'll see what i mean. When the engine is running, items such as the rings heat up, making them expand, and therefore close up the gaps and tolerances (to an extent). If the engine is cold, there's no such expansion. Both of these reasons make it possible for fuel to seep past the rings.

Hope that helps.

Thanks for the explanations of how and why. The fuel has leaked in through the vacuum hose as the fuel tap was leaking out of the bottom drain spigot from the fuel tap (which was where the vacuum tube was wrongly attached to) so the carbs weren't leaking the fuel, the vacuum hose had filled and was dripping it in....

Basically guys, I'll be changing my oil and filter!