The diagnostic kit was brought into action at Geoff Jones' in Tylers Green, Bucks whose long Jupiter restoration project had suffered a stall due to engine problems. At Bill Lock's 70th it was decided to have a team effort, so Richard Gane, Bill Lock (transported by Diana) and myself started with ignition timing. Anyhow suffice to say we found, the timing to be 180 deg out, two spark plugs (of course they were Champion) not functioning, and tappets incorrectly adjusted. Then the distributor was found to be unstable (so was swapped) and finally one carb was found to be not functioning properly. The latter has been left to fix for another day.
I hope people have learnt that a methodical approach is necessary.
There is probably no set way to approach such a situation with people saying the car ran, and I think it is valve timing. Basically, listen and remember, but do not let it alter a systematic approach.
In this case, we checked to see we had a spark at No 1 plug that had been removed, that this occurred at TDC ( by using a flexible probe down a cylinder and feeling for TDC, and making sure this TDC occurred when No 1 cylinder was on its firing stroke with both valves closed (by removing rocker cover).) The TDC was double checked with the mark on the flywheel. We failed first time round to check that a spark occured on all four plugs when they were removed. Even this is no guarantee that a spark will occur at cylinder compression, but in this case it showed that two of the infamous Champion plugs failed even on this simple test. Do not assume a new plug is a working plug.
However, the cylinder compression test revealed one cylinder down on compression (90 psi) and this was fixed by adjusting the tappets which had been done using the old method in the manual and not using the method that superceeded it ( adjust valve when opposite valve is fully open) e.g (No1 inlet when No2 inlet open). In most cases the valve opening was over twice what it should be as the valves had been adjusted using the old method. After adjustment all cylinders were within 5 psi of 120 psi. Valve timing was not checked as eventually we decided the initial pops and farts and loud bangs were ignition timing.
The car then ran after a few more swaps of the order of the ignition leads, although not smoothly and a timing light revealed a wayward distributor, caused either by worn bearings or worn mechanical advance. So the dizzie was changed, not easy as the drive shaft needed changing and the 'stupid' 90 deg ignition leads needed unscrewing. I always use a plug-in vertical cap, better water insulation and easy changing of firing order. Care is needed to make sure that NO 1 lead is going to the correct terminal , alignment can be deceptive. Also make sure your rotor arm is fitted!!! Static timing was checked on contact breaker
The car now ran better but still would not accelerate, vacuum advance did not seem to be working but that was not the cause. By putting one hand over one carb inlet, we discovered the car ran better on one carb. Probably a main jet or bowl gasket failure. Something for next time. We had blown out the bowls and checked the jets previously, so some spare bowls or a spare carb will be pressed into service next time.
Here is Richard contemplating the next move.
Please click thumbnail for better image.