Ignition Timing

[stebec]

I want to check my ignition timing this week with a timing gun on my 1975 Spitfire 1500, what is the best setting for the timing?

Steve

[Nigel Clark]

Start with the workshop manual static setting of 10 degrees BTDC. Make sure valve clearances are correct (10 thou cold), the spark plugs are in good condition and there are no air leaks around the carbs (carb to manifold gaskets, vacuum hoses and manifold to cylinder head gasket).

The ideal ignition advance for your engine depends somewhat on the condition of the engine, and the octane number of the fuel used. 97 RON super unleaded works well, 99 RON Shell V-Power or Tesco Momentum is even better.

Using your chosen fuel, the optimum ignition timing is best found by trial and error. Most of our engines run best with a degree or two more advance than specified in the manual. With the engine warmed up and the ignition timing set as per the manual,try advancing the timing slightly, usually the idle speed will increase. Go out for a drive and - where safe to do so - floor the accelerator at around 2,000rpm in top gear. Listen for the characteristic sound of pre-ignition or pinking. The aim is to find the most advance the engine can take without quite pinking.

Take care though, too much advance will damage the engine, while the optimum setting will give crisp performance and good fuel economy.

Nigel

[dougbgt6]

Yup, what Nigel says, advance till the revs stop rising then back a gnats, go for a run, pinking? Back a gnats more. Or by vacuum, advance till maximum vacuum then back one bar. Fun to do them in tandem and find they're both correct!

Doug

[johny]

To add Steve, in case youre not sure, pinking is a light rattling/tinkling sound you can get from the engine and as Nigel (and Triumph) says you will hear this when accelerating in 4th on the flat but it should stop by the time you reach 2000rpm. Its usually worse the hotter the engine and if it doesnt stop then the timing is too advanced👍

[AlanT]

Don’t be worried it your timing ends up quite a bit advanced of factory settings. Mine requires this with modern fuels. There’s no power at factory setting level.

[dannyb]

My 1500 spit was set at 17 deg btdc on a rolling road.

Danny

[Wagger]

On 22/02/2024 at 12:25, dougbgt6 said:

Yup, what Nigel says, advance till the revs stop rising then back a gnats, go for a run, pinking? Back a gnats more. Or by vacuum, advance till maximum vacuum then back one bar. Fun to do them in tandem and find they're both correct!

Doug

Many of us have desrcibed how we do this in the past.

I set the throttle so that the engine is revving between 2500 and 3000 rpm. Distributor clamp previously slackened and vacuum pipe blocked. Turn the Dizzy until you achieve peak revs then go back a tiny amount. Clamp the distributor, unblock the vacuum tube and do a test drive.  If it pinks when going up a hill at 2000 rpm, retard it a little at a time until it does not pink.

Those of you with a Dizzy with a vernier adjuster are luckier than me. No vernier on mine, sadly.

I have done this on all of the classic cars that I have worked on and it achieves the best results wrt economy and power delivery. Stick to using the same fuel. If you have High Compression (over about 9 to 1) use Highest octane  available.

Some of our cars were designed for 5 star leaded fuel that was 101 octane. Unleaded fuel burns totally differently from unleaded so there is hardly any point in setting the timing to what the book states.

[PeteH]

Question?. The static timing for a 13/60, according to Haynes is 9Deg. However the engine in Plum, is an ex 1300 Spitfire (HC?). I assume the static timing will be different? but by what?.

Pete

[dougbgt6]

I'll get my coat. 

Doug

[Pete Lewis]

just use your ears  as said   simpluze 

Pete