Spitfire Spitfire Engine Surge

[doates]

Hi Again,

I have been able to temporarily empty and seal my floats; hopefully until new ones arrive.

I have been fighting an engine surge (70 Spit) for a couple of months now. At idle it surges from 800 to 1000 rpm's every couple of seconds. It does not start surging until the engine gets hot. I have set timing to 6 degrees BTDC, adjusted carbs to their initial settings per Haynes and fiddled with them until it sounds like they are sucking the same amount of air (tube in ear) numerous times with no success. It starts great and idles well until it gets hot. When driving it around the neighborhood it seems to lack power and I can feel the surge (not as extreme as at idle). I have sprayed the carbs and all intake joints with carb cleaner and it does not cause a change in idle.

I just took my distributor apart and it looks pretty clean inside except that there are two different sized springs inside. Is this normal? Very little play in the shaft.

After only a couple hours of running the cap and rotor show some wear and crud build up on the terminals.

The plugs are slightly sooty but not extreme.

Any suggestions greatly appreciated

Thanks...Dennis

 

[poolboy]

200 rpms suggest 2 things, at least to me. Either the Vacuum Retard is acting up or the Throttle Bypass Valve is floating.
The only part that doesn't fit into either Scenario is the correlation to temperature.
There is a Temperature Compensator, but I've never seen it make that much difference in engine speed whether it was fully open or fully closed.
And yes, there are 2 different springs on the centrifugal advance weights.. The engine has to be beyond idle speed, though,for them to even start doing their job.

 

[doates]

Good News - I got the engine to purr at 825 RPM's. The bad news is that the timing is at 28* BTDC. I had never heard of "vacuum retard" but is mine acting up and what do I do about it? I will take it around the block tomorrow to see if it will actually get up to the speed limit.

Thanks for any suggestions

 

[TR3driver]

Your timing mark must be wrong. I don't believe a 70 Spit would have vacuum retard anyway; according to the factory service notes it only had an 'extended' advance curve so the timing could be set retarded at idle.