Car taxd and out on the road but same problem as last night, car has 1700 xflow with twin 40s.

Runs ok fan kicks in temp at 80 - 90 and down to 80 again
put new thermostat in as it was running without and flushed the system
runs ok then after you come back froma drive and take it out again it splutters and back fires and dies, cools down and ok and then starts the cycle again.
1 & 2 plugs sooty as if over fueling.
Any ideas, i have put extra vents in the bonnet and exhaust is wrapped with heat shield.
Possible air lock?
Please i want to enjoy the summer

I would be looking at starting with a compression test.........

From you description there absolutely nothing wrong with your cooling system.

It could be a heat soak problem or a leaking float valve on the front carb.

My first suspect would be the front carb is overfilling due to the residual pressure in the fuel line from the pump. It may need a new float valve or float level reset or it could be an excessive fuel pump pressure problem. What type of fuel pump are you running ?

A heat soak problem can often be fixed by putting your fan on timer so it runs for a minute or so after the engine is stopped.

Heat soak can also show up a fault in the coil or ignition module

Check your valve clearances as well. Too tight (even just a bit) and you'd get the symptoms described

Fan has a timer, a bit blackish smoke if you rev it from standstill, running unleaded fuel electronic ignition. Will check the valve clearence at weekend a nd check the carbs.
Its git a facet fuel pump pressure regulator set 2 on the dial.

Well checked the float levels, starting with the second carb which was set at 6mm the first carb which looks like was causing the problem was at 23mm. Now both set at 12mm as specified just need to try it and get them set up.

Fingers crossed

[Edited on 3/5/13 by kj]