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Engine tune... idle speed

Rui Guimaraes

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I've just decoked the cylinder head on my mk1 GT6 with new valves and guides and made the engine setup.
I'm happy with the overall result specially with the high rev performance when warm, but I notice two things that are not allowing me to achieve the perfection....

1. Unstable running cold with the choke pulled.
2. Idle speed 950 to 1000 rpms (can't go lower than that)

1. I've tried to setup the choke acceleration cam/bolt like the manual describes (around 1/16") but if I let it like that, the engine stalls as soon as I pull the choke (lack of acceleration and too rich). To work I have to put the bolt head touching the cam without the choke pulled.
I've opened the carbs and they look to be perfect. The only strange thing is that they are assembled with 1.75 needle valves instead of the 1.5 standard ones. Do you think that this could be the problem? Should I change them to 1.5's?
2. Can the needle valves affect the idle speed also?

Engine setup parameters:
Fuel: 98 octane
Static timing: 10º
Carb mixture: 3 turns each
Valve clearance: 0.25mm
Contact breaker gap: 0.4mm


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