Engine Tuning Help Please

[JuNK512G]

Trying to sort my friend's 1098cc Trav which suddenly went seriously out of tune on Drive It Day, backfiring, no power & stopping for short periods.
I have found a number of things wrong, the most serious of which is really bugging me. Less than a year ago the timing was set to 3degs BTDC, I found it to be in the region of 10degs After TDC which no doubt explains the running problem. It's been suggested the timing has jumped but I just can't fathom how that could happen, the Dizzy was completely tight & no evidence of movement. If it did jump, then obviously it could do it again.
Without at this stage going into the several other things amiss, has anybody any knowledge or suggestions in this matter please.

[Jefftav]

How are you checking the timing? Statically or by timing light? Yos say there was other problems with the car it may be worth listing these in case they have any bearing. My first thought would be the vacuum advance fitted to teh dizzy as the diaphram can go on this which might affect the car when you are driving.

[bmcecosse]

I'm constantly amazed with the fascination with measuring 'the timing' to the finest degree! But whatever it was - if you now advance it - does the engine run properly ? As Jeff says - worth checking the vacuum advance to see if it's working as it should.

[JuNK512G]

Thanks for the replies so far, I wanted to understand first if it is really possible for the A series timing to jump, so I didn't want to muddy the waters with the rest of the problems so here we go.
I checked the timing first with a light bulb then with strobe.
Having reset the timing, yes the car drives fine.
The dwell was 70 which I've reset to 63.
Gunson colourtune check showed bright yellow which I've reset to bunsen blue.
Vacuum advance was not working at all due to the metal tube being quite loose at point of entry to vacuum unit, I've managed to tighten the brass union nut & seems to be okay now.
Points condition okay but were .012 gap which I've reset to .016.
Trailing 1/8th inch of Rotor heel slightly burnt.
Brass segment of rotor loose, with burning in evidence at centre contact point.
So far I've only done one cylinder compression, (hot & dry) with Gunson pressure gauge, results are disturbing,
No 1 - 200psi. No2 - 180psi. No3 -165psi. No4 - 200psi. Handbook pressure states 160psi to be correct.
Sparking plug colours, No1 Light. No2 Brown. No3 Light brown. No4 Brown
Valve clearances, 7 at .012 & 1 at .013 therefore as near perfect as one can get.
Negative earth battery terminal was loose, coil appears connected correctly but I haven't tested the polarity at the spark plugs yet.
Although the car wasn't boiling, it appeared very hot so have changed the thermostat although on test this appeared to work.
Replaced the by-pass hose but there was nothing wrong with the old one & no blockages.
Flushed the rad, nothing significant.
Sods law, after re assembly, the disturbance had created a hole in the casing of the pump,(not the one underneath) & that's where I'm at at the moment.

[alex_holden]

Gunson colourtune check showed bright yellow which I've reset to bunsen blue.

I found that when you get the mixture right, it burns a bit yellow at idle but immediately goes blue when you rev it up.

[bmcecosse]

Only problem I can see there is the rotor arm - the 'timing' was probably seen as being different because the vac advance wasn't working - no - it can't jump. but as points wear it will slowly change. Colour tune is waste of time - just test with the little lift pin. The comp checks are exceptionally good - 200 psi would normally only be obtained on a competition engine - so I suspect the Gunson ( ) gauge is reading high. The lower reading particularly on #3 suggests a damaged valve/seat - but if it's running evenly enough I would leave well alone for now, and keep an eye on it.

[JuNK512G]

Just to finalise this one, having righted the obvious wrongs, the car runs well again. I guess the main culprit was the non-working vacuum advance unit although I still can't understand how it could have become some 10 - 15 degs retarded on tickover.
I rechecked the cylinder compressions & found them all 15 psi lower pro-rata than the first test supporting 'bmcecosse' suggestion of a faulty 'Gunson' gauge.
Many thanks to all for the help.

[bmcecosse]

Even so - 185 psi is still exceptionally high for an unmodified engine. No matter - all being same is the main thing, not the actual reading. The vac advance pulls the timing up at idle - so when it fails - the timing is horribly retarded at idle.