Lux Prima

The first start of any engine after a rebuild is always a bit of a fraught time. There are any number of things that can go wrong, some of them spectacularly, but mainly just irritating things like oil leaks that need sorting out. In order to keep suspense levels down, I’ll start this update with a quick precis. The 750 Sport started first time on the button and didn’t leak anything. But I’m getting ahead of myself… Let’s take a bit of time to run through what needed doing to get to this auspicious point in the project.

Last time out, the bike was on its wheels, with electrics (mostly) present and correct. There were obvious things that hadn’t been done (charging system, clutch etc.) but they could wait. Fuel and exhausts were the next things on the list. I pulled the old fuel hose out of the box, and it was obvious that it was never going to go back on the bike, as it was completely rigid. A bit of Tygon hose was therefore ordered, along with an 8mm T-piece, and a Dell’orto 120 main jet to make up the return branch of the system.

The jet is there it act as a restrictor in the return branch, to ensure that adequate fuel pressure makes it to the carbs. This was simply soldered into the T-piece:

The hose was then cut to the right length (actually it’s still a bit long in places, but it’s easier to cut bits off than add them back on again) and put together on the bench.

I know that Tygon hose is a bit expensive, but really it’s so nice to work with and lasts so well that it’s money well spent. As for fitting a brass, rather than plastic T-piece, there were good engineering reasons for doing so in that I could solder the jet into it. But mainly I went for brass because it’s so shiny. The fuel tap was then fitted to the underside of the tank, and the tank was dropped onto the bike. Of course it didn’t fit. The fuel tap was now hitting the gas valve on the rear shock – which was easily fixed by removing the shock and rotating it 180 degrees before refitting it. This was made a thousand times easier by the simple act of having an Abbastand to lift the bike by the swingarm pivot, rather than having to arse around with axle stands. With the tank now fitted and plumbed in, attention could turn to the exhausts.

Again, I pushed the boat out slightly here by ordering stainless steel studs and copper nuts – hopefully they should last more than 12 minutes before seizing solid. And really, that’s the most interesting thing to say about the exhausts. They just kind of bolted on with no drama at all.

Oil was dropped into the right hole (Motul 5000 – not the poshest oil in the world, but perfectly adequate for a low-revving twin) and I was deeply happy to note that it all stayed in the engine, with none of it decorating the garage floor when I turned the engine over on the starter motor to build up oil pressure. I’d pulled the battery out of the teeny Morini to do this, and it was really only just about up to the job. Once I’d determined that yes, the oil pressure light was going out after a few seconds on the starter I disconnected it and stuck it back on charge. I then robbed the battery out of the 748 and quickly realised that not only was it a much stronger battery, but it also was the perfect size to fit the 750. I have no idea why I didn’t pull this one out first.

All I needed to do, then, was to add fuel and press the starter button. But, that had to wait a couple of days. I’d promised James that he’d be on hand to witness the first attempt at starting, and so this morning he bounced into the garage with 5 litres of super unleaded and a big smile. And a bacon sandwich. The fuel was dumped into the tank, and I hesitantly switched the ignition on. I was fully expecting fuel to start leaking from every orifice once the pump was running, but no, it all stayed where it should have. I handed the fire extinguisher to James, and pressed the starter button…

…nothing doing. After a few seconds churning the motor, I remembered that I’d disconnected the plug leads earlier when I was turning the motor over to build up oil pressure. I popped the plug leads back on, pulled the choke cable, and pressed the starter button again…

Yeah, you can tell by the look on my face just how surprised I was. It started easily, and ran smoothly. We retired to the kitchen for a cup of tea to celebrate.

After the fifth cup, I wandered back out to the garage to run the bike a bit longer to get some temperature in it, and while the tickover was certainly a bit lumpy, once it had ran for five minutes or so it was perfectly happy to idle with the choke off.

I had another cup of tea to celebrate. And ponder the next steps. I already knew that the bike would be coming apart again immediately after the test run, but I need to determine just how far to go at this stage. The original plan was to strip things all the way back, and get everything repainted and make a proper job of it – but if I do that, I’ll not be able to ride the thing this year. So I think a compromise is in order… I’m going to pop some 17″ wheels in there to make it useable, rebuild all the electrics properly, get the shock serviced, and just ride the thing. Even this won’t be cheap – but it’s going to make it at least (hopefully) affordable.

Next update may be a good few weeks away then – and before I go any further with the 750 I need to fit new tyres to the 748, and change the oil and filter ready for when the weather breaks and we finally get a sunny day. But for now, things are very much progressing to plan in my pink and fluffy little world.