Plumbing problems

Plumbing problems beset my ride yesterday. I headed out in the Salisbury direction and found the bike started missing on the Warminster bypass. I slowed down and it cleared. I knew it was the return of the fuelling problem I had before Winter. I was trying to persuade myself it was nothing.

On the way home, she stopped altogether three times. I could see that the fuel filters were dry so there was no doubt it was fuel starvation. My guess is that when the bike heats up, the rubber fuel hoses soften and then close up where they bend. I think it is both the vacuum pipe to the rear of the fuel tap and one or both of the fuel hoses to the carbs. Each time, after the bike had cooled I could see fuel flow into the filters again and so could do some more miles.

So last night I took it all apart again to take out the fuel filters so the hoses would have an easier route to the carbs. And in doing so I managed to snap one of the t-pieces I'd plumbed in to link the two sides of the system!!! So I had to pull the carbs out too so I could remove the broken stub etc.

Ironically, I could see that the carb throats and inlet rubbers were wet with fuel. It is ironic bearing in mind the problem I was trying to solve was not having enough fuel. That suggests I set the float heights too generously. So I'll be adjusting them by 1 - 2 mm whilst I'm at it.

On the plus side, with the carbs out I could do something else. And so I have a nice new heavy duty lead from the starter solenoid to the starter motor ;-)

Failed tank liner

I have been having intermittent problems with fuel starvation. The effect of this has been running on two cylinders, cutting out, then restarting after a few minutes at the side of the road. I know it is a fuel starvation problem because the bike would run on either cylinders 1 and 2 or 3 and 4: both combinations are served by both coils so coil failure could be responsible. I have had trouble with one or other of the petrol pipes doubling over and cutting off the supply to the left or right pair of carbs. Also, I have fitted two clear fuel filters into the petrol pipes and so I could see them empty of fuel when the bike has come to a stop, and then gradually refill. I figured that flakes of the liner were probably wrapping themselves around the filter that is integral with the petrol tap, thereby restricting the flow of petrol through to the carburettors. I had previously had a go at removing all the loose liner from my petrol tank, including fishing in it with a spring-loaded grabber tool and then draining it entirely. I managed to get a lot out and thought the remainder was sound. However, the return of the starvation problem suggested otherwise. I was pretty sure that once again the failed liner was at the root of the problem so I decided to try getting some more of it out.

I used my grabber tool again and soon found it wasn't hard to fish out large flakes of the liner that had come loose inside the tank and was floating about in the petrol supply.

In the photo above, you can see the size of these flakes in relation to the petrol filler.

So after about 30 minutes of work, I managed to get a considerable amount more of the failed liner out of the tank. I'm pretty sure there aren't any other large flakes there right now but I'm equally sure more will come looses and foul the fuel outlet once again.

Fuel cap

I wanted to make sure my fuel cap was functioning properly. I have had some problems with the breather on the identical item on my 900. It has occasionally failed to admit sufficient air into the tank to allow fuel to exit, especially after a period of high speed running.

The cap is an aircraft-style flush filler cap, operated with a key in spring-loaded mechanism. The key hole is itself hidden under a sprung cover. This cover was loose, not snapping shut, and the key was not centering after the cap was pushed home. Not a big deal but I thought I'd see if I could clean out the components and restore some snap to the action.
The main components of the cap are visible above, including a lid with rotating centre that is hinged to an alloy ring; a retaining tang which is drawn back by the two pegs on the rotating centre; a small spring which forces the tang out to retain the lid by clipping under the forward edge of the tank's filler hole; the main fuel seal which is held against the tank's fuel filler hole by four small springs; a tang retaining cover, and steel retaining disc and two screws which clamp the tang holder and seal in place.

The fuel tank breather is a small air passage that runs from a little hole in the tang retaining cover, through a casting that contains the lock barrel, and through a pair of diaphragms to another little hole next to the hinge. The tank emits a rather attractive humming, whistling noise when in the sun or cooling down after a run. The noise is made by fuel vapor escaping, or air being drawn through these diaphragms.

The little holes are indicated by the tip of a screwdriver in the pictures above. The left-hand picture above shows the cap without the main fuel seal in place. The four small springs visible around the rotating body apply pressure to the main fuel seal to ensure it works effectively. The right-hand picture shows the cap reassembled.



The cap assembly is retained by four screws into the top of the tank. One is under the lid, preventing the cap from being removed without unlocking it first, the other three are allen-headed screws that pass through the periphery of the hinge ring. Two of the allen-headed screws are just decorative. A rubber dust and dirt seal fits into the top of the tank first, followed by the cap hinge ring.



I cleaned off all the corrosion from the components and lubricated the rubber seal with rubber grease, and the spring-loaded tang with copper grease. I replaced the inner screws with stainless items. Job done.

The best LeT plans of mice and men ...

So with the carbs in place and fuel supply sorted courtesy of my piggy-back tank arrangement, the great post-rebuild start-up moment had arrived.

At least that was the plan. The reality was a lot of ny-ny-nya-nya-nya-nya-nyaaa. Nothing. ny-ny-nya-BANG-ny. BANG. Exciting, certainly. Rewarding, no.

I pulled out the spark plugs to make sure they hadn't fouled with the Redex I had put down the bores and intakes. Result: sparkers looked great when they came out. Refitting just gave more of the BANG same ny-ny-nya. BANG.