SQ4 - batteries

  For the record, let it be known that I have today fitted a second battery to the system on the Square Four. This returns it to the layout that we ran for the first 7 years or so of its time in service. We now have 19 amp hours of capacity extended from the 12 amp hours we've been running for the last year.

We are back to running these VRLA batteries again: 

A few miles run later in the day showed one-kick starting, there is no fuel leak and the idle is fine. The ammeter showed a charge; the battery monitor also showed a charge and did not go out of the green zone. Since most of the run was quite slow, perhaps I should not be surprised that the battery charger spent a little time returning the batteries to full charge at the end of the day?

SQ4 - idling again

 A 30-minute run out this evening confirmed that adding PTFE tape to the volume screw put us on the right track to improve the idle and hesitation problems on the Square Four.

It needs more work, adjusting the idle speed down, further adjustments to the ignition timing and probably some small changes to the idle mixture as well but it is starting well and idles smoothly. 

SQ4 - after the service

 A few little teething troubles appeared after the recent service, most notable of which was the oil pressure. Normally the oil pressure sits at 75 psi when cold and rolling at main road speeds, dropping to 25 psi idling after 15 miles or so.

Today, it was going up to 75, but intermittently dropping to 40 or so - very odd. I bled the Morgo again:

When that appeared to be happy - there were no bubbles I turned my attention to the relief valve.

See that bit of debris half way along the spring? I cleaned that out, and after a suggestion from Richard in the AOMCC, I changed the ball and reseated it.

I then rode to Cromer and back, clocking up about 13 miles - until it warmed up, it sat solidly at 75 psi and was still showing 50 psi when I got home. Back to normal.

It’s a bit snatchy at low speed. Initially I thought this was carburetion (not that I have changed anything), then perhaps transmission snatch, but all is normal there.

I’m going to retard the timing a bit.

SQ4 - idling and a idle mind

 Some while back I had taken part in a forum discussion about a Square Four with a poor hot idle, in which one of the gurus had drawn attention to the absence of a critical notch in the only gasket specified for the Solex. Yesterday, I was out on a little tootle around Holt and Cley, and boy was it hot. Of course, coming through town on the way home you remember that it doesn't idle very well when it's hot.

A few minutes searching the AOMCC forum archive revealed the post I'd contributed to in 2018, where the notch-less gasket problem had been explained. I pulled the Solex apart this morning and lo & behold, no notch:

Furthermore, you can see how the gasket has been squashed into the slot, obstructing it further. It was a simple matter to cut the notch:

Starting the bike up, it seems to start easily and idles happily - but that might have as much to do with resetting the point gap from 5 thou back to the regulation 15!

Debris in the pilot circuit

It's amazing what a small piece of debris can do. Coming back from North Walsham the other day, close to home, the SQ4 decided to die every time I closed the throttle, which made slow speed cornering somewhat unnerving and junctions, especially one on a hill, something of a strain. Ever tried to kick start a heavy bike while holding the throttle open and the front brake on with one hand?

Fortunately, the starter circuit and the main jet were fine, and I got home under my own steam.

Fuel for the pilot system comes from the float bowl and is controlled by a jet screwed into the hole in between the float bowl and the emulsion tube:

It passes into the large hole in the top of the carburetter:

And out of the round hole positioned at 10 o'clock in the square flange:

Then it passes through the gasket into the annular machined groove in the throttle body

The pilot mixture passes into the hole at 6 o'clock. From here, it goes forward to the idle screw, and passes around there into the engine when the throttle is closed; additionally, there is a hole near the butterfly which provides additional mixture from the pilot circuit as the throttle opens, to prevent a flat spot occurring before the main jet is active.

Stripping the carburetter down revealed a little gremlin in the pilot jet:

Poor focus macro picture of a jet with extracted debris

Quite enough to disrupt the flow of fuel into the pilot circuit. All fine now.