ignition timing for 25/65 cam in 1500

[hypoid53]

I have just reset my 25/65 cam timing on my Spitfire 1500 using a vernier gear wheel to achieve more accurate cam timing and it occurs to me that the 'standard' Spitfire 1500 ignition timing of 10 degrees BTDC, should not necessarily be correct for this cam.
As it is a Mk3 Spitfire type cam I checked that models timing and it is 6 degrees BTDC.
At 10 degrees I cannot get the idle speed below 1000rpm with correctly set up carbs and there are no vacuum leaks. At its recent MoT my CO reading was only 1.2% instead on 2.5 so I richened it up a bit!
I have now reset to 6 degrees BTDC (vacuum advance disconnected) and achieved a more reasonable 850/900 rpm idle, so I will try that for a while.
Has anyone else had similar issues with the 25/65 cam in their Spitfire?

[That Man]

hypoid53 wrote:

I have just reset my 25/65 cam timing on my Spitfire 1500 using a vernier gear wheel to achieve more accurate cam timing and it occurs to me that the 'standard' Spitfire 1500 ignition timing of 10 degrees BTDC, should not necessarily be correct for this cam.
As it is a Mk3 Spitfire type cam I checked that models timing and it is 6 degrees BTDC.
At 10 degrees I cannot get the idle speed below 1000rpm with correctly set up carbs and there are no vacuum leaks. At its recent MoT my CO reading was only 1.2% instead on 2.5 so I richened it up a bit!
I have now reset to 6 degrees BTDC (vacuum advance disconnected) and achieved a more reasonable 850/900 rpm idle, so I will try that for a while.
Has anyone else had similar issues with the 25/65 cam in their Spitfire?

Personally i would say that the petrol you are using would have more effect on the static timing than the cam, you must remember that these cars were designed to run on 4/5 star leaded petrol, so even with a completely standard engine the original static timing wouldn't necessarily be optimal. Trial and error always works for me, just keep advancing the timing a degree at a time with a road test until it starts pinking then back a degree. Also you may find that the advance curve is not right for the cam you now have, only a rolling road session will sort that out.

Gordon

[drofgum]

hypoid53 wrote:

.
As it is a Mk3 Spitfire type cam I checked that models timing and it is 6 degrees BTDC.

hypoid53,
If you check you will find that it is also the Mk2 Spitfire type cam (it was the same part number). Mk2 used 17 degrees static advance. Once the cam is changed it is very unlikely that the advance curve in the dizzy will be right, it would be good luck if it is acceptable throughout the rev range.
                                                                Cheers,
                                                                Paul