We've had a couple of half-decent weather days, so after our discussions at the meeting on Sunday, thoughts have returned to getting the cars ready for the various trips etc over the summer. The S is pretty much there, but I have still to look at the Vixen's carburettor settings. Even with the mixture screw turned in as far as it will go, the engine still runs, so I think it's either getting too much air, or not enough fuel, and that's leading to the hesitation when you start to put power on from idle.
Now, I could take it to a "tuner", but who? Their first question would be "where do I plug in the computer?" Who still does proper "tuning" of old-skool carb cars?
Let me explain my cynicism... a long time ago, I had an NSU Prinz (you can read about that under "cars I have owned" in the menu bar on the left there). When I got it, it had even less power than the nearly zero bhp that it was born with. I took it back to the garage I bought it from, who said that they had "crypton-tuned it" and there was nothing wrong with it.
Useless bastards - so I decided to look at it myself, and found that one of its two ignition leads was shorting, where the insulation had melted through against the edge of the exhust manifold. It was only running on 1 cylinder. I found it by getting an HT shock right up my arm, whereupon my mother, standing nearbly, discovered that I knew a lot more swear words than I had previously disclosed in my innocent young life.
Many years later (but still over 30 years ago!) I had a Vauxhall Astra 1.3L as a company car. I had to get it serviced at a main dealer in Glasgow, where I worked at the time. When I got it back, it was misfiring like hell, and they wouldn't look at it because everyone had already gone home. I had to drive 34 miles home, and then 34 miles back the next day, at a max speed of 30 mph...
They took it in first thing, and then called me at around 5pm to tell me it was ready. When I turned up, they said "no fault found" and handed me the keys... well, it could hardly reach the end of their car park. Once again, they wouldn't look at it because everyone had already gone home, but the service manager took me through to their empty workshop and explained that he had a staff of fully-trained expert mechanics, and a £35,000 diagnostic machine. "If they can't find a fault using that machine," he said, "there isn't a fault"". He was very polite, but I recognise a "fuck off" when I hear one, so again I had to drive 34 miles home, at a max speed of 30 mph...
By this time I was so pissed off that, company car or no, I decided to look at it myself. It took me less than 5 minutes to isolate cylinder number 1 as the misfiring culprit (by removing plug leads one at a time), and another minute to diagnose that their new spark plug, inserted during the service, was "outside unfucked specification". The ceramic had broken under the ministrations of their expert spanner-wielding gibbon, and was covering the spark gap, so no firey. I horsed in another spare plug and it ran as sweet as a very sweet thing... in less than 5 minutes, with elementary tools. Oh and a half-functioning brain.
Back to the main stealers next morning - hauled the service manager to the counter and said "remember you told me about your fully-equipped experts and how they could find any fault? Well, they didn't find this," as I handed him the spark plug. "I found and fixed that non-existent fault in under 5 minutes." He was suitably embarrassed and offered me back the price of the spark plugs. He recognised the undertone of "stupid arrogant tosser" when he heard it though, so I negotiated the refund up to the full price of the service, just to encourage further training in the dying art of fault diagnosis.
I was watching an episode of "Bangers and Cash" the other night, and they had taken in a Crypton Tuner. Most of them didn't know what it was. One or two knew what it was, but had never learned how to work one. The general opinion was that they were shite at the time, so they were totally useless now... QED.
Anyway, I digress. Suffice to say that I would rather have a go at this myself than try to find someone old enough and good enough to do it for me.
So I've done a bit of research, and found some basic jets and settings for the Weber 32/36 carb. Then on a Ford owners website, I found slightly different recommended settings for a 1600 crossflow. What I don't know, is what jets are in my carb - I took it apart in October 2024, wrote them down, then lost the bit of paper...
So on Tuesday, I decided to investigate by taking the top off the carb - first remove the air cleaner, then disconnect the wee choke lever, remove the fuel line and undo the 6 screws holding the top on the carb.
This is the top of the carb, where you can see the two air corrector jets in the top. There are also two main jets in the bottom of the bowl (under
those air jets) and two idle jets in the sides of the carb (not really visible in this photo). I take all of those out, noting exactly which goes
where, and their sizes.
Here's the removed jets for the primary inlet (left hand side) and secondary (right hand side).
This is a diagram that I found online that shows the position of these jets, and the recommended sizes. I also found a slightly different list of settings on a Ford Owners club website for a 1600 crossflow GT engine - which is what mine is. More on that in a minute.
Here's a wee table. Who doesn't love a table, right? (not in the physical sense, obviously, shagging your furniture is not "de rigeur" in polite society). The first column shows the jet settings in the diagram above. The second column shows the settings from the owners club website. Pretty similar, but with a bigger primary main jet and smaller secondary air corrector.
The third column shows the jet sizes that I took out of the Vixen. Much smaller jets on the primary side, slightly more air on the secondary side. I have no idea why they have been set as they are, that's just how I found them.
At this point I have to stop and rack my brain trying to remember how carburettors work. I know that at idle speed, the air corrector and the idle jet work together to meter the amount of fuel reaching the idle mixture screw. My engine is idling with the mixture screw almost all the way in, so that maybe suggests that the air jet isn't big enough?
Also, the primary main jet seems to be much too small - could that be leading to the "flat spot" as the carb transitions from "idle" to "open"?
After much consideration, I decide to leave the secondary jets as they were, but increase the jets on the primary side to the sizes for the 1600 GT.
Here's an updated table, that includes the revised jetting that I settled on.
Then I check the float height. Here's the top of the carb upside down with the floats in place.
To set the correct float height, you hold the carburettor top vertically so that the tab is just resting on the needle valve. For a brass float, the bottom of the float should be 41mm from the face of the top surface. Then you turn the carb top the right way up so that the float is hanging, and the bottom of the float should be 51mm from the face of the top surface, as shown in the left hand diagram. Mine was about 2mm too low, so the needle valve would be closing slightly too early, which would lead to a slightly weak mixture. I bend the wee tab on the needle ball valve slightly, to set it right.
The diagram on the right is for plastic floats, which are a different shape and more "floaty".
So with that all set, I reassemble the carb, reconnect the choke and replace the air cleaner. I wind out the mixture screw to a starting position of 3 full turns from closed, and start it up! Once it has warmed up a bit, I adjust the mixture screw to "best idle" and then reset the idle speed. Then the mixture again and then the idle speed. After a third time, it's idling fairly smoothly at around 850 rpm. I couldn't get it to idle below around 1,000 rpm before.
I don't have a rolling road, and it's getting dark, so no time for a test drive. I switch it off before it overheats, and I'll try it again tomorrow.
There we go - a day that sums up this website! Half a page of slavering pish, and half a page of technical discussion (which may well also turn out to be slavering pish, if you know anyuthing about carburettor tuning). Life is all about balance.
