Project Snicket, Engine Tuning

Now that everything seemed to be running OK, we had oil only where oil should be, and coolant was mostly where it should be, it was time to do some old school tuning.

The main things you can tune on an older car like this is the fuel mixture, the timing and the idle speed. These are all the things I needed to check and set.

Obviously before you can even considering tuning the engine up, you need to know everything else is in good shape. I had just gone over the ignition system and replaced the cap, rotor, points and leads. The spark plugs although old, once gapped correctly were OK. The fuel was recent, the pump worked, the carb was clean and I had no vacuum leaks.

Step one was to use the knowledge of where the timing marks are (as mentioned in a my previous post about them), and using a timing light try to see where the timing is. I don’t have many photos of this, because you need about 4 hands to actually check the timing (one to hold the timing light, one to hold the mirror, one to turn the distributor, and one to stop the cables getting in the way).

My timing light is an old Optilux unit that I purchased many moons ago. It only gets brought out occasionally, but I’m always happy to have it. A good timing light is one of those things that if you buy a good one to start with, it’ll last many years of occasional use. Mine has no adjustment, no readout, and no tach. Just a simple light.

A timing light needs four things. Power, Ground, Signal and something to point at.

With no battery in the engine bay (or even a “jumping” point like modern cars) you need to source 12V from somewhere. I chose to grab it from the starter solenoid feed, where the big brown wire (constant power) connects to the solenoid.

The Ground was taken from the bolt above the starter solenoid

The inductive signal clip goes on ignition lead number 1, with the arrow pointing towards the spark plug. Cylinder 1 is the closest to the fan

I found it quite hard to hold in the button on the light, whilst holding it, and the mirror, so I used a zip tie to keep the button pressed.

I found setting the mirror up so you can see where the marks would be, and then pointing the light at the mirror (instead of trying to point it into the hole) so the mirror reflects the flashing light onto the flywheel worked best. With the engine running (at the lowest idle I could get without it stumbling, which I guess would be about 1100rpm), warm, and the vacuum advance disconnected and blocked at the carb, using this method I tried to find the timing marks, only to find that they weren’t visible at all.

I tried using the fine adjustment on the distributor to get the marks to come into view. The fine adjustment is the two bolts on either side of the distributor mount. The holes these bolts go through are slotted, so you can turn the distributor and make small adjustments. One bolt is circled, and the other should be where the arrow is pointing (mine is missing that one)

I went full retard on the slot, and nothing, no marks. The distributor was already at full advance when I got it.

The next step was to tighten those bolts back up, and loosen off the main clamp, for maximum adjustment freedom. This circled nut tightens the clamp, and loosening it off allows full freedom of turning the distributor.

I turned it a further 20 or so degrees and BAM, I saw the marks finally come into view. I set the timing to the 10 degree mark. It’s a little more advanced than the 7 degrees Haynes says it should be, but it’ll be fine. I’ll run 95 or 98 octane in the car in the future anyway.

I locked down the distributor, check the timing again, and we were firmly on 10 degrees. Don’t forget to reconnect the vacuum advance, which is blocked off by the black cap in the below photo

With the timing in the correct place, the engine was running smoother, and would allow me to lower the idle, but I still had a stumble. Looking at the spark plugs I was running very lean. I had a very white spark plug with only minor traces of brown.

The engine also stumbled, and stalled when the piston lifting pin was pressed. This is a clear sign that the mixture is too weak, and I needed to enrichen it.

To enrich the mixture you use the jet adjusting nut hanging under the carb. This nut raises and lowers the jet assembly, allowing more or less fuel into the carb. The nut is circled here

Its pretty hard to see, and harder to get to. You cannot get a normal spanner on it easily, so I found it easiest to turn it with my fingers. One hand on each side of the carb, using both of my index fingers to turn it.

To enrich the mixture you want to lower the nut, turning it down, away from the carb body. If you were looking down at the top of the carb, you want to turn the nut clockwise to enrichen, and counter-clockwise to lean the mixture. In my case I had to turn the screw a hell of a long way, the mixture was very lean.

Having come from my last tuning experience being the Speeduino, where everything is basically handed to you on a screen, with figures, gauges and logging to work from, this was far more… personal. This kind of tuning is all done by feel and ear.

When I was turning the nut, I could tell I was getting close as the idle speed started to rise, and the engine smoothed out. If you turn the nut too far and the mixture gets too rich, the idle speed will start to drop off again. You want to stop at the peak of the idle speed. When you start to get to the point where you think you are near, after each adjustment give the throttle a couple of good blips and wait for the idle to settle again. Happy? Tweak and blip again. Sometimes you may need to rev and hold the engine at a higher RPM for a little to clear any excess fuel in the inlet, and then continue.

The piston lifting pin also comes in really handy here too. With the VERY lean mixture I had, as soon as you looked at the pin the engine would stumble, the rpm would drop and it would stall. This pin was invaluable to identifying where the mixture was. If your carb doesn’t have the pin you can do the same thing by sticking your finger in the carb inlet and lifting the piston with you finger a couple of mm.

What you want with the piston lifting, is for the idle speed to either stay the same, or in my case since I left it a little on the rich side, the idle to jump up a tiny bit and then settle again.

I still have a little tweaking to do to lean the mixture, as I left it on the safe/rich side, but its happy for now. The idle is now a lot smoother, the engine is more responsive and its happy for me to drop the idle speed down for a nice tick over.

The idle speed is adjusted by the screw inside this recess at the front of the carb. I use a narrow flat blade screwdriver to turn it. What it’s actually doing, is it’s just a long threaded pin that just pushes on the throttle linkage (that the cable pulls on) under the carb. Not technical, but works.

I took the car for a quick hoon around the block and it feels a lot more lively now. Its faster, and doesn’t bog down or hesitate. No signs of a misfire anymore either.

One thing that makes me happy is the fact that it starts so easily. With the engine warm, it starts immediately, with no other inputs.

So with the timing set right, the mixture set close enough, and the idle nice low and smooth, it’s actually a nice little car. Cant wait to get it legal and see what it can really do.