Speedo Wobble!..... Fixed

Had a problem on the way to Gaydon heritage motor museum where the speedo appeared to be connected to the rev counter so I disconnected the speedo and made my way home in convoy with some lorries to make sure my speed was steady and sensible (no speedo in average speed camera zones is very tricky!)

I got home and had a play. When stationary I could rev the engine and the speedo needle would fly round. Clearly something wrong going on.

After being very worried with an oscilloscope seeing all sorts of noise on the speedo sensor wire, and on the main power wire I took the top off the distributor (not the cap, the coil cover) and noticed that where the three pin plug fits into the dizzy cap, the terminals in the cap had been pushed up so presumably they weren't all making good contact. I wiggled it all around to make sure the plug was actually in and started the car and hey presto! Speedo no longer connected to the rev counter!

Here are the offending terminals in their "pushed down and fixed" state:

Another thing I trialled was my "Neighbour Happiness Device" aka some aluminium ducting attached to the exhaust that trail outside the garage with baffles on the end. With this ingenious arrangement I can sit in the garage with the door closed and play around to my hearts content with mixtures/timing etc and have vastly reduced noise.

Pipes were attached on with copious amounts of aluminium tape as I didn't have large enough jubilee clips

Jetex silencers shoved in the end with the good old stainless scouring pads:

Lasted about 30 seconds until I gave it a bit of a rev up to 2000rpm or so before the ali ducting was literally blown apart

and one of the baffles ejected from the other end:

Gaydon Heritage Motor Musem

Dizzy Tweaking

Here is the recurve kit trial-fitted. The weights they supply were very poorly finished and I had to drill out the holes on the centre plate so it would fit! Bit nasty.

This is the dizzy with original weights and centre plate.

Carb on fire

Well today was interesting. My distributor advance recurve kit arrived so I removed the distributor to swap the weights and springs. My first mistake was removing the distributor - I realise now I could have done this with it in the car but oh well.

The recurve kit was very badly made and when I put the rotor back on the distributor it wouldn't sit down properly and wouldn't snap back with the spring tension. Original weights and springs back in and the advance mechanism works as it should.

It all started going wrong when I refitted the distributor. I found TDC on cylinder 1 by removing all the spark plugs and turning the engine by hand with my finger over cylinder 1 spark plug hole. You can feel pressure on the compression stroke, I know my TDC mark is correct on the harmonic balancer so that was done. I adjusted the distributor so the rotor was at the cylinder #1 tower in the dizzy cap. Fine so far. I knew the timing wouldn't be perfect but I figured we would get it started then I was ready with the timing light to adjust it.

Started the car, it caught and ran for about 5 seconds then POP and a small flame out the top of the carb. Stopped the engine. I suspected perhaps the timing was too advanced so it was igniting the mixture when the intake valve is still open and blowing through the carb. Pulled all the plugs, rechecked TDC and set the dizzy conservatively retarded (read "most definitely retarded") from where it was.

Started the car again and it immediately went BANG again, this time a foot high flame roared out the top of the carb. I assumed this was bad.

I then went away and read the internet for a while and discovered if the timing is too far retarded you can also have a backfire.

Plugs out again to verify TDC and...... came to remove the plug on cylinder 2 and CRACK, the ceramic insulation shattered. No spare plugs. Early night then.

12 degrees BTDC? Check!

Verify its definitely on compression cylinder 1? Check!

Rotor lined up with wire #1 tower (white paint mark on machined dizzy body) Check! - yet still flames out the carb!

I eventually resolved this, it was just massively retarded. I failed to appreciate the fact that the spark comes when the rotor leaves the contact i.e. the trailing edge. Combine this with the fact that I underestimated how small a rotational adjustment of the distributor is required to start piling on the advance/retard and it's not difficult to be 10,15 or 20 degrees out. Now I know what I'm doing I won't fall in this trap again if I have the dizzy out in the future. I have to keep reminding myself that I've never really done any work on an engine before apart from changing spark plugs so this is all still a learning curve.

More engine tweaking parts

 New bits arrived in the post - distributor recurve kit and a variety of accelerator pump nozzles.

The recurve kit contains advance limit bushes so I can bump up my initial timing to get smoother lower rev running without going too high on my total advance. Currently I'm at about 12° initial and 34° total (22° mechanical advance). Plan A is to fit 18° limit bushings so I can run 16-17° static and 34-35° total. I know that around 17-18° static is the sweet spot for idle vacuum so we will see how that goes. EDIT - It turns out that the accel kit is rubbish. The Moroso kit is the one to get - see this post: Moroso kit fitting

The accel pump nozzles will hopefully cure the lean bog. I've got the pump adjusted for the biggest shot (volume) but the speed its delivered is restricted by the nozzle size.

Other jobs half started - I checked the float height and it was fine at 7/16" but I didn't check the float drop - should be 1".

I also haven't yet measured my fuel pump pressure.

In other news I had to fit a new fan temp controller. The old fan relay died and latched itself on, then seems to have burned out the temp controller. I've got a higher current rating relay to replace the old one. Its all mounted on the inner wing just behind the radiator so I expect excessive heat has killed it, both engine heat and heat from the higher current draw of the bigger Spal fan. Unless I want to do major rewiring the relay has to go back in roughly the same place so I will make a heatshield out of sheet ali.