I have at last got a cold start primer tap working well today, but before anyone says where did you get it? I have to point out that has not been easy, I have had to make and tested several versions before reaching this happy position.
This is the reproduction tap which happened to come from Agriline, but the general view is that other suppliers are probably offering the same thing? I mentioned earlier in this thread, this tap makes a jet which misses the hot coil, so no flame
I tried to make an atomising spray head the same as used on plastic plant spray bottles, but didn't get the same result. They seem to work on the principle that a flat round surface is positioned very close just behind the small diameter jet hole, I assume so the liquid has to move fast and then suddenly change direction, my model engineering skills didn't seem up to making that work.
Next I modified the outlet of the tap with some 1/8" dia copper tubing and silver soldering. the tube bent round at 90 degrees with the intention at least of pointing the fuel directly at the coil. I made this too big and it fowled on the coil while screwing it in which nearly damaged the coil.
Next I researched and looked at other 'low pressure, liquid only spray jets', and found that some have narrow slot across the jet. I think the principle is that the otherwise round jet column of fluid coming from the jet touches the sides of the slot and is broken up in doing so. The slot was made by a junior hack saw blade which had been ground to a knife edge, then the slot was nipped up a bit in the vice, the result isn't very pretty with the repeated silver soldering not helping.
The jet hole behind can just be seen here,
Here is a view looking into the maniflold which I had removed it to make sure I had jet pointing straight on to the coil. The tap didn't tighten up in the right place so it remains about 1/2 a turn slack however the copper pipe from the fuel tank is tight and it alone prevents the tap from rotating.
This one produced a reasonable spray, not a fine mist but it does point straight at the coil and more importantly it flames as soon as fuel is pumped, and the engine starts very nicely. I realise that this solution is not for everyone, I only wish I could point towards a simpler method, but it works for me and now at last I can move on to other restoration jobs.
I have found that the '40 seconds' advised period of preheating before pumping fuel, is rather long, the coil seems to be quite hot enough in 20 seconds, and doesn't really get much hotter if you wait longer.
One thing that I am aware of is that the compression is quite low on two cylinders, this is very noticeable when turning the engine over slowly with the starting handle. It is probably suffering from past ether abuse, in time I expect to rebuild the engine with new liners pistons and rings. when this is done hopefully it will start anyway unless it is very cold, in the mean time I still have a useful tractor.
Regards
Ian
I