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 - a little investigation

 Of course, a broken motorcycle can’t be left for too long, especially when your daily rider has been persuaded from your grasp.

There were a few problems to investigate, possibly associated:

• There was a carburetter leak, or possibly flooding 
• The battery indicator was showing far too much red, considering the 60 miles the bike traveled yesterday 
• The bike refused to start twice yesterday, needing pushing to the top of a hill and roll-starting 

Putting the CTEK on the battery had it charging normally, but it was very flat:

But why so flat? According to the ammeter, the battery does charge and indeed, it was charging on the way home. I did notice the ignition had been left on as Tom had complained the engine wouldn’t idle and it had died when he arrived. I currently believe this has more to do with the battery than anything else.

There is no leakage from the battery with the engine not running and you can measure normal currents with lights on, though with the LEDs fitted to this bike these are minimal. The ignition circuit draws 400 mA without the engine running - I think it would be a good idea to try this with the engine running.

I've also realised that the red spot ammeter doesn't show very much deflection at all - I calibrated the one on the Huntmaster against my bench power supply and there is a lot more movement. I wonder if the Square Four has a 30-0-30 ammeter.

A simple test with a 35 watt bulb revealed that the ammeter appears to be 15-0-15 - while I was doing this test the multimeter was reading 5 amps.

As a first step towards sorting the fuel leak, I removed the drain plug/main jet holder and finding no new fibre washer of the right size, sealed it with a wipe of Threebond 1215. That fixed the leak, and there is no evidence of flooding. 

Amelia started first time like she always does.

As to the idle, I don’t know yet as I haven’t got it warm enough to close the bi-starter.

SQ4 - a ride out

 My son made a surprise visit today to borrow one of my CTEK battery chargers. He's not seen the Huntmaster yet and we agreed that I would ride with him halfway home so that he could have a go on it. He was very pleased with it.

However, when he arrived on Square Four he was complaining that it wouldn't idle. I noticed that he'd left the fuel on and the ignition on, and the battery condition light was showing red. I got it started by bumping it down the hill and rode it to North Walsham; it was okay ish but it obviously wasn't happy at low engine revs - but it was charging.

After a bit of a chat at the North Norfolk Motorcycle Museum, I left to go home but it wouldn't start at all - the carburettor was dripping and the battery condition light was still showing red which suggests the battery is not holding a charge. Again I'd left the fuel on, so maybe it was overflowing and the float valve is not working properly, or maybe there's a leak. 

Eventually I got it started by rolling it downhill and and rode it home like a bat out of hell at up to 60 miles an hour. It was charging, and going fine and I got home safely though the front brake is a lot worse than the one on the Huntmaster. 

I put it on the battery charger when I got home and the battery condition light showed red for several minutes, which is unusual - normally if I put it on charge it will go to green straight away. After a couple of minutes it went to solid green which means it's charging or fully charged.

There's something wrong here.

SQ4 - all done

This might be the last post on the Square Four for a little while - it's next trip is likely to be to my long-term storage at my son's house, where I shall go to collect W/NG to come back for some work - but more on that later .

Today I took the Square on a 15 mile round trip to Cromer to do some painting and do the final shake down on the carburettor and ignition settings. Yesterday I fitted the new mixture screw and this needed a little bit of tweaking to get it spot on and I increase the idle speed slightly - though I think I've got it too high. I also retarded the ignition slightly. 

The good news is that it's running very well. It starts easily and it will pull away cleanly in traffic from low speeds. It flies along on the open road so all in all I'm very happy.

Here it is resting at Gresham church.

Getting home, it occurred to me that in a similar fashion to the light switch yesterday I had not touched the horn for a long time. Since I fitted this horn, which came straight from eBay, I don't think it's had any work done to it and as regular readers will know I've become reasonably adept at adjusting these horns.

I gave this one a little tweak to make the sound a bit more intense.

SQ4 - idle mixture screw

 I recently took a punt on an eBay sale for a mixture screw for a carburettor from a Rolls-Royce B40 engine, the one used in the Austin Champ. It was listed as a Solex part and looked very much like the one on the Square Four.

I struck lucky - the parts are exactly the same.

This is the old one, and measures 4.86 mm at the end of the thread

This is the new one, which measures 4.92 mm at the end of the thread:

So perhaps not a huge amount of wear. It does appear though that the nose of the old screw is notched - I don't know if you can see it in this picture:

I fitted the new screw with a t-bar and put it back in the carburettor with a wrap or two of PTFE tape. 

We'll have to see if it makes a difference.

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 - idling

 The Solex is back on, but I still have a problem with idling - but it's different. The bow in the inlet flange that I removed has changed it's behaviour at idle, as you might expect, but in tuning the idle I've realised that the idle volume screw is very worn. 

I've ordered a new one:

While I wait, I've wrapped the old screw with PTFE tape which should help.

SQ4 - Solex again

 Some while back I retarded the timing on the Square Four and improved starting greatly, but it is still running roughly coming off idle and when coasting. Nothing I do to the carburettor seems to improve this so I have resolved to have another look. 

Stripping off the carburettor is quite easy and another inspection revealed nothing new. However looking at the gasket faces (something which I would do every time with an Amal carburettor) revealed a bit of a surprise: 

You can see here, by the dark line along the edge of the flange that it is by no means flat, which can lead to a weakening of the mixture. A few minutes on some 200 grit wet and dry paper revealed this:

A few minutes more work improve that even further. 

The internal mating face between the throttle body and the float chamber and jet castings was nothing like as bad:

This face did show a little distortion, but it was easily removed. You will note that one of the throttle disc screws is missing - I removed that one but as you can see the other one didn't come out without a fight. The reason I removed it is revealed by this picture: 

See the light around the edges? This is ostensibly completely closed! What I needed to do therefore was to remove or loosen the butterfly screws and realign the disc so that it was properly closed. In reality it's not essential that it closes because the throttle stop is there to provide some idle speed and the butterfly will always be partially open. This kind of leakage will prevent you idling as slowly as you might want to so it pays to reduce the gap as much as possible. I replaced the screws and got a marginally better result:

I will work on this some more when the proper screws arrive. These should be raised countersunk M4 screws, around 10 mm long.

SQ4 - a useful modification

 I've been fiddling about with the ignition timing this week as there had been some significant hesitation coming off-idle and some poor performance at low speed - what we used to call 'kangaroo petrol'.

I retarded the timing a bit and realised the bike had stopped kicking back on startup, and the slow running was better, and it would fly along like a bat out of hell - but coming off idle still wasn't as smooth as I'd like.

In the end, after fiddling with the idle mixture and getting nowhere, I stripped the carburettor.

I didn't find much. Some debris in the float chamber, the flange fixing to the head looser than it should have been, and one of the float chamber screws was loose. I blew out all the jets and ports with carb cleaner and found everything clear.

Putting it back together, I added this little tee to the idle mixture screw to make it easier to adjust (it's a bent bit of brazing rod, soft soldered to the brass screw), and used some Threebond on the flange.

We'll see what happens.

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!

Solex Idle Circuit

I've known for some time that I didn't have a drawing of the Solex 26 AHD on the blog. Today, coincidentally, someone was asking about the jet locations and problems with idling on the AOMCC Forum. I uploaded a drawing and Pete Silson provided some wise words, and an annotated the drawing to suit. Before we get to that, note that the fuel follows the orange highlighted path before it reaches the pilot air bleed jet, when the blue mixture path begins:

I don't believe the notch under the choke tube has any effect on tick-over. The four usual sites for blockage of the pilot mixture path are shown in the diagram below.

Air leaks anywhere in the mixture path (blue in diagram) cause erratic tickover. Blockage of the pilot jet (3) weakens the tickover mix, blockage of the pilot air bleed (4) richens the tickover mix. There are two small holes either side of the butterfly (1 & 2) which can also get gummed up - the size of these are important so best to blow them through with air rather than poking with wire.

The tickover mixture is governed by the ratio of the Pilot Jet 070 (0.7mm) and Pilot Air Bleed 150 (1.5mm). The tickover mixture is further adjustable using the Volume Control Screw - clockwise for weaker, anti-clockwise for richer. The tickover speed is adjusted by the throttle stop on the main butterfly.

The ratio of the Air Correction Jet and the Main Jet and the Emulsion Tube controls the mixture over the whole rev range. The Air Correction Jet has more influence at higher revs.

The jets are illustrated in this post. Apparently Mikuni were agents for Solex at one time and Mikuni jets fit these carburetters.

Square Four - Improving the mixture

 I learned from the folk on the AOMCC forum that the mixture can be adjusted by changing the float level, as in other carburetters. I hadn't thought of this approach with the Solex because the float acts directly on the valve and there is no arm to bend, for example.

However, the collective consciousness revealed that the float valves could be fitted with several washers if necessary, to lower the valve and hence the fuel level, leaning out the mixture. Like many others, I had replaced the fuel valve fibre washer when I rebuilt the carb, with a single washer of about 1 mm thickness, but apparently there can be up to 3 mm of thickness there.

Since my bike was using quite a lot of fuel and, judging by the state of the silencers was clearly running rich, I added a second washer. 

A plug chop revealed that the change had been a success. Previously, I had been running NGK B5HS plugs as my B6HS, equivalent to standard fitment, had been sooty. After the washer was added, I was able to revert to the B6HS and they were a much better colour.

Haven't you done enough shaking down?

So another day, another road test. After the weekend, where I checked out the B5HS plugs (pale grey centres, all the same - as expected) and fixed a very dodgy crimp in the distributor circuit and filling the tank, I took an early evening bimble along the lovely A149 North Norfolk coast road, into the setting sun. As usual, the SQ4 was fine for the first few miles, though I thought a little more reluctant to rev from a closed throttle than normal. We stopped for a break and a picture at Blakeney:





There's a narrow lane down to the beach here, maybe 300 yards down a hill which you do at 20 mph or less - idling, essentially. At the T junction at the bottom, there was a reluctance to rev and I coaxed the bike to a parking place where I enriched the idle mixture half a turn thinking that it had been reluctant to come off the idle jet since leaving the house.

A few more miles, and once out on the open road again she was flying. A little stumble now and then but generally great, until I got to a little village called West Runton, which has a mile or so of descent down a narrow lane into the village centre - again, 20 mph max, throttle closed, followed by a short hop over a railway bridge. By the time I was at the bottom, opening the throttle would kill the engine and there was no way I was getting over that bridge until the engine had cleared its throat. Once on the open road - more or less OK again. I'm convinced it gets very rich on the overrun, or descending hills on closed throttle.

So, back in the shop I am thinking that I have the idle mixture screw set way too rich - but it's only two turns out. My second thought is that there is an internal leak - possible in the bi-starter, or possibly the bi-starter is not closing fully.

We'll have to pull the carburetter off again. I found a useful site here, which takes a while to load but has some great pictures of a 26 AHD strip, refurbish and rebuild.

Solex 26 AHD data for the record...

For the record, the jets from my Solex 26AHD are recorded in this post. Here's a diagram to help identify them:

Starter Jet

Pilot Jet

Main Jet

Pilot air bleed

Air Correction Jet

Float Valve

Starter Air Jet

You can download a copy of the Solex Instruction Booklet here.

Solex Emulsion Tube Repair

Regular readers will know that I've had a few problems with misfires lately. I've cleaned the carburetter several times, reviewed and serviced the ignition system and fitted a tufnol spacer and a heat shield to reduce the carburetter temperature. This has worked to an extent, but I still have an occasional misfire. Cold, my 1951 SQ4 runs beautifully – it’s smooth and responsive. Hotter, it seems to stumble when opening up again after slowing for a roundabout or some other obstruction. This stumbling clears itself quite quickly, after which the bike will pull as it should. Occasionally you will get a cough or the feeling of holding back.

Stripping the carb revealed that the emulsion tube was not in great shape, it was slightly bent and has a long hairline crack along maybe half of it’s length. The bend is probably due to it's location and the fact that it is possible to remove the float bowl with the carb in the bike, which leaves the emulsion tube vulnerable - if you are not careful removing the float bowl, you can catch it on the emulsion tube and bend it.

One of my theories is that the area of the float bowl casting forming the well around the emulsion tube is still exposed to engine heat, though I believe I can grip this with an ungloved hand after a run. The tufnol spacer and the heat shield have made a huge difference to carburetter temperature.

The first job was to straighten the tube. I put the straight section in the lathe, and brought a dead centre in the tailstock up to the air jet, to indicate the eccentricity. A bit of judicious bending, guided by the centre, had the emulsion tube straight again.

This is the emulsion tube, after my wiped solder repair. That crack was along most of it's length which would clearly upset the mixture.

Now, David Jones has new emulsion tubes for £20 plus postage, so that would be the way to go. However, if this doesn't cure the misfire, and I think the misfire might be down to ambient temperature, I'll be glad I kept that £20 in my pocket.

We'll test it later this week. Ambient here is now anywhere between 10 and 18 C, so we may not be able to give it a proper test until next summer...

Shields Up, Mr. Scott...

In the everlasting challenge to keep heat away from my carburetter, I have added a heat shield to the previous insulating gasket.

I know from test rides that the radiated heat from the engine is as significant as the conducted heat, so I have attempted to deal with that with a stainless steel heat shield, mounted on the front float bowl screw. Petrol boils at 95 C, and we have seen temperatures in that region on the float bowl - and we have heard the fuel boiling. So, with some spare time and in 'metal working mode', here it is:

It's bent up from a piece of 0.9 mm stainless steel I had knocking about in the shop, cut to shape with snips:

This notch is to clear the starter jet on the front of the float bowl:

Here it is in position:

It's only mounted at the top, so we should expect some vibration and potentially a fatigue failure. We'll see how effective it is tomorrow.

Oh, and by the way if you are wondering why it says 'Meyer' on the side, have a look in your kitchen cupboards. It's the bottom of a stainless steel casserole. Waste not want not!

More Cake

Another cake run today, this time out on the SQ4. The chain guard is not sorted and is going to need to come off again for some serious adjustment!

The weather was great though and the trip to Cley and back was uneventful, save to remind me what a lovely part of the world we live in. Here's the SQ4 enjoying a break at Glandford:

After a 24 mile round trip with no misfire, but rather slow (there is a lot of traffic around here in the summer) we have these results, taken with the engine running in the yard and measured immediately upon arrival:

• 210°C on the fins near No.2 spark plug
• 151°C on the inlet manifold flange - near the offside carburetter stud
• 109°C on the carburetter flange, 1/2" from the 151°C measuring point but on the other side of the phenolic spacer. That's a 42°C differential across the spacer.
• 87°C on the float bowl. This is much higher than usual and I think reflects the fact that the day was not windy and I was travelling rather slowly. There's more convected energy than I thought and I've decided that a heat shield may be in order

Whilst there was no misfire,  I think I could detect that the engine was not running as happily as before.

Ambient was around 23°C for most of the trip. I measured the other cylinder head temperatures as well and added them to my chart with some previous tests:

When I returned, I noticed a small leak from the oil tank cap. I'd given it an extra twist before I left in an attempt to seal it, so I'm sure the seal is not thick enough.

Dealing with Fuel Vaporisation

As I wrote a few days ago, whilst out on a shakedown run I had put about 6 miles under the wheels of the SQ4 when the misfire appeared. Power was really down and I had to drop to third on all the hills. Forgetting what the Four can be like in hot weather I was worrying about the ignition system, but managed to crack on home - I was overtaken by a military M20 at one point, as I could only manage 20 mph.

Back home, I put the bike back in the workshop and drained the oil tank, the sump and removed the filter. Sitting by the oil tank, I could hear the fuel boiling in the float chamber, and my Infra Red thermometer revealed that the float chamber was at 80°C and the carburetter body, near the cylinder hear flange was over 100°C - and remember, I had already spent 15 minutes draining the oil at this point.

I was clearly going to need the carburetter heat insulator that I bought a while back (in 2015!), which I had not fitted since I had the distributor the wrong way around - with the square 'condenser bulge' forward. This reduces the space available for the carburetter/spacer combination.

You'll see from the picture that there is very little room for the spacer before the carburetter hits the distributor, even with the bulge facing to the rear.

Pulling off the carburetter, it is immediately obvious that the existing, original studs barely have enough thread to allow a full nut to be used to retain the carburetter, so there is no chance of a spacer fitting in there as well:

Fortunately I have some 5/16" 303 stainless round bar knocking about, so we can make some longer studs. Here goes:

I've made them 1/4" long than stock. At this point I realised that whilst I have 5/16" BSW taps, I have no die. Now there will be a short pause...

RDG produced a suitable die, two days later:

Using the tailstock die holder made short work of the studs, but one of them has a CEI section which is a little longer than it wants to be I think:

Trying the carburetter in place, an unforeseen foul condition is revealed when the BiStarter hits one of the tank mounting bolts:

As expected, one of the studs is marginally too long in the CEI section:

There is still a few millimetres spare before the float bowl contacts the distributer:

So that's it. Stud adjusted, the carburetter goes on nicely with the 3 mm phenolic spacer, a paper gasket and some Threebond. The rear offside tank bolt has to go in afterwards.

Preliminary results show that it is pretty effective. Warming the bike up after the work, at rest, reveals the following temperature readings with the engine running:

• 162°C on the fins near No.2 spark plug
• 107°C on the inlet manifold flange - near the offside carburetter stud
• 39°C on the carburetter flange, 1/2" from the 107°C measuring point but on the other side of the phenolic spacer. That's a 68°C differential across the spacer.
• 22°C on the float bowl.

Whilst this looks encouraging, we must remember that this is a result of conducted and radiated energy - any convected heat is going upward towards the tank, not rearward toward the carburetter ; a 10 minute warm up is not a valid representation of 25 miles in a 25°C ambient at 70 mph, and we are not at full operating temperature yet.

But it's encouraging nonetheless.