Oil, socks and misfires...

Some of you may know that I have been troubled by misfires just recently to the effect that the good old Solex has been stripped more times in the last month than in the 70 or so years since it was manufactured, and the distributor is not far behind.

Link in the oil line modification I did a while ago, and the calorific nature of the engine's energy-conversion activities and a pattern might start to emerge, especially when a lot of those misfire-ridden journeys occurred when we were blessed with warmer weather.

Lo and behold, one day I was working through the ignition system and removed the HT leads, to check them over and apply some heat-shrink numbers to the cables. It was then that I found the oil, sitting in the five little pots on top of the distributor cap and manfully attempting to insulate the distributor from the HT leads, and succeeding some of the time.

Since I cleaned all this out, I have not suffered a misfire (but the weather has turned colder, so no pre-natal poultry accountancy services required just yet).

Ariel knew about this problem, providing a rubber sock to protect the distributor connections from oil and water:

Distributor sock 5239-49

As you can see, its a curved tubular cover which envelops the whole distributor cap and leads in one conical tube. Here's one, fitted to  'barn find' machine.

And another - though this one looks like heatshrink to me:

No, this is not the Sorting Hat from the Harry Potter movies. It's a shroud I've attempted to make from a very large piece of heat shrink:

It looks marginally better in this picture:

Here are some close-ups. It goes right up under the tank, passing over the tank mounts:

I'd really like an original one, but for now this is doing the job sufficiently well to prove the case for the cause of the misfire.

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 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...

Misfires & Winter Jobs

I've tracked down an annoying misfire that may be of help to others. After a while, my Square starts to idle very roughly; so much so that I have had the carb apart for cleaning several times. The misfire seems to occur when I am on the way home, and I thought that it was happening when the engine was hot.

I've started to realise that it is down to the No. 3 plug terminal. When the engine has been running for 50 miles or so, there is enough vibration to back off the nut on the plug, with the result that the plug terminal sometimes shorts against the inlet stub...

Better HT cable routing required. I also noticed that my HT cable routing fouls the Bi-Starter mechanism...

It's time to think about winter jobs on the bikes, especially as the W/NG is nearly done and I will have at least two to choose from. For the SQ4 these are:

1. Fix the speedo and get the blurred dial replaced
2. Get a new slow-running screw for the Solex
3. Decide on removing the indicators or not - I need to do something, because the indicators are regular tungsten bulbs and the load causes the LED headlamp to flash with the indicators. This is a bit disconcerting at night...
4. Replace the front wheel bearings with sealed bearings
5. Replace the front inner tube which leaks slowly
6. Look at the brakes again as they bed in
7. Make a new tool roll
8. Fit a couple of transfers
9. Change the oil tank for the one with a good filler neck thread

And for the W/NG:

1. Grease the forks & replace the missing nipple
2. Maybe replace the fork bushes
3. Tighten the brake torque arm anchor or weld it in
4. Make a T-bolt for the exhaust clamp
5. Adjust and lubricate the primary chain
6. Have a look at the clutch
7. Change the regulator to a V-Reg
8. Fit a couple of transfers

All good fun! And if I get a bit of bench space, and any spare time after that lot, I might start looking at the various welding jobs on the Huntmaster tinware...

Oops

Well, I got out on my test drive, and it feels much happier - smoother, more torque at the bottom end...

Unfortunately, about 5 miles in, a misfire appeared and the engine stopped. Having experienced this many times during the fuel filter saga, I was quick to look for fuel supply problems and cracked the fuel supply banjo to find all was well. The bike started again, only to stop again after about 100 yards - this happened once more, and then I was close enough to push it home...

Charging had looked good on the ammeter from the first day. All the lights worked perfectly, apart from one indicator which persistently rotated around to face the floor, but in general everything had been fine. However today, when I had the bike running again, switching on the lights would kill the engine.

The Lucas C35SD gives 70 W at about 1700 rpm which equates to 32 mph in top gear, but when you are running around town the ignition, brake light and frequently used indicator loads soon drain the battery, which appears as a fuel-starvation-like misfire. I cursed that fuel line again until I realised what was going on, and a CTEK battery charger came to my rescue. Actually you need about 20 W for the ignition alone, or about 3 Amps; in top gear, you get 3 Amps from the generator at an average of 23 mph – these bikes are really not for town use.

My 1951 Mk1 has a 20 Ah battery bank hidden in the Lucas GU11E style fibreglass box. I'd be surprised if you could even get to the shops with the earlier small battery...