53000 miles: Fuel leak and carb clean

Yellow petrol residue on the alternator

I noticed I was arriving at home smelling of petrol. Although I find a bit of a petrolly whiff has its own appeal, it is not something my wife appreciates. There came a point when it was obvious that something needed to be done. That point was seeing petrol dripping onto my alternator. Not good.

I thought it was due to a faulty float bowl seal on the carburettor for number two cylinder so it was a case of getting the bank of carburettors off the bike and giving them a bit of a birthday. I figured the air filter could do with a clean anyway and, after 53000 miles, I decided it would be wise to change the cam chain (next post). So Ruby was going to get a big birthday.

24 years and 52,995 miles

As it happens, I think it likely that she was made in July or August in 1991. I don't know for sure. She was registered 1st of September 1991 but with chassis number 544, production having begun in March and building up to a rate of about 50 machines per week during the year, my guess is that she was constructed any time from mid June to Mid August. So happy 24th birthday, Ruby. She would be having a reasonable run out afterwards because I had an international trip to do for work, flying from Heathrow, and I had decided to ride there, stowing my bike gear in left-luggage for the duration of my time abroad. FWIW, that trip worked out well - free parking for the bike and £20 for left luggage.

So the full list of jobs were: diagnose and solve fuel leak, clean out carb float bowls, clean and re-oil air filter, change air box for a better second-hand part I'd bought from Trevor, change cam chain and check valve clearances. The first four are here.

I have found that the top of the motor tends to accumulate road grit over time. It surprises me because I have inner panels that sit in front of the exhaust pipes and fill the gap above the oil cooler and below the water radiator. Anyway, it is helpful to brush off the cam cover before removing the plug leads. I remember I'd got the coil low tension connectors muddled up when I first tried to restart the engine back in 2012. So when I removed the coils, was very careful to keep note of which connectors belong to which coil. 

It is always a bit of a fight to get the carbs out. There is not much room between the airbox and the inlet stubs, and the rubber is ageing. I don't rush at the job, straddle the bike so I can get a good grip on both sides, and put a block against the front tyre to guard against the risk that I'll roll the bike off its stand in my pulling and pushing. The air filter was satisfyingly dirty. 

I have had a bottle of RAMAIR foam filter oil for years. I got it for my old GS650 Kat. It has a solvent that evaporates to leave a tacky coating. Good stuff. It just needs engine degreaser to clean it up. I was lucky enough to have a sunny day so the filter dried out quickly and then took the RAMAIR oil very well. 

 The old air box was severely cracked and my attempt to repair it with filler rod and a soldering iron had finally given up. The replacement box was in great shape and, I realised, had a slightly different design from the broken one. It has a plastic frame that retains the filter and this frame has recesses for four long stainless screws that clamp the sides of the box.

Replacement airbox, with filter frame including
recesses for through-bolts on each side. 

 The carb float bowls contained a fair amount of a red dusty residue. The seals showed a bit of alloy fur but nothing that looked like a leak. Perplexing but I cleaned them up and reset the floats 1mm higher than before (15.5 instead of 14.5). The motor had been running a bit rich, from the colour of the exhausts, so I was happy to make this change regardless of the leak.

The carburettor floats being reset to 15.5mm.
Fuel pipes visible beneath 

 To cut a needlessly long story short, I reassembled the carbs, installed and tested them for leaks. The leak was still there - but this time, with the tank out of the way, it was clear that the leak was actually from one of the fuel pipes, just above one of the blue plastic T-pieces I had installed. So I replaced it with some double-walled 5/16 fuel hose. That really did fix the leak.

View of the reoiled filter through the left end of the airbox

Running on two cylinders

When I started my Trophy 12 for its MOT, I was disappointed to find that she dropped onto two cylinders after a couple of minutes. She was running beautifully the night before. Lovely even beat. What could have happened? I had my appointment booked though and thought it might be some muck in the carbs or maybe something that would clear as the engine warmed up. 

Not so. Warming up didn't make any difference. Maybe one of my coils had failed. Each coil controls a pair of cylinders so it was possible. However, the two cylinders that were not running were numbers 3 and 4. The pipes on these cylinders were cold. One coil runs cylinders 1 and 4, the other runs cylinders 2 and 3: it could not be a coil/ignition problem. So attention turned to the fuelling side of the equation.
 
I had thought that the two fuel lines were to ensure an adequate feed of fuel at high speed, and that they fed a common gallery for all four carburettors. This was an assumption. Looking at the carbs, I now see that one fuel pipe feeds cylinders 1 and 2, the other feeds cylinders 3 and 4.

To cut a long story short, I found that I had pinched one of the two fuel lines that runs from the fuel tap to the carbs. The previous night, I had not bolted the fuel tank in place. Of course, I wouldn't take to the streets with the fuel tank insecure so I had fastened it down the following morning.

To remedy the problem, I took a close look at the routing of the fuel lines. One of them pushes on to the rear of the tap, the other pushes on from the right-hand side. I had used much thicker fuel lines to replace the hardened originals. This meant that they need more room to physically fit in tight spaces and require bends with a wider radius. I had inadvertently routed the bike's wiring loom along the main frame tube exactly where the rear fuel line would need to turn when the tank is fastened. So I solved the problem by pulling the wiring loom further around the frame tube and securing it with an additional cable tie. That gave the fuel line sufficient clearance to bend around the frame tube without too much difficulty.

The result: all working beautifully. The engine's creamy smooth thrust was restored, allowing me to start enjoying the bike in the next few days. It was still very much in shake-down mode for fault finding and rectification. A great feeling.

Carbs and filter

The carbs were in good shape overall - just a bit of muck in the float bowls and the needles were muddled up (the inner two are a pair and the outer two are a pair).

The code for original 1200 carbs is visible on the side: 1240010. 

Other than the swapped needles, the only other problem was corrosion on the float bowl mating surface, visible as white powdery substance, which lead to a fuel seep. 

The airbox had cracked had been taken apart before and badly reassembled. The box-to-carb rubbers had been refitted upside down. This is visible in the picture to the right as an inlet ribbed section at the bottom of the rubbers. These should align with air pressure equalization apertures on the top edge of the CV carbs.  

The box had also failed on the lower edge where the two halves screw together. It is not designed to be disassembled - when the air filter is passed its service limit, the idea is to swap in a whole new air box complete with new filter. However, the fact that is screwed together rather than glued or plastic welded means it is possible to remove and clean, or replace the filter with an aftermarket part. I read somewhere that the original filters were made for Triumph by PiperCross. They are available on eBay.  Lots of people replace them with K&N filters though. 

Airbox disassembled - note ragged side on lower left-hand edge.
This is where the plastic had failed, probably by over tightening.

I chose to clean my filter and to repair the splits by welding them up with a bit of plastic filler rod and a soldering iron. I also drilled holes for a through-bolt either side. I made this up from stainless rod and a couple of stainless domed nuts locked up against regular hex nuts on the inner edge.