1978 700 series 70hp mercury high idle

[Vinsta]

Hi all,
I cannot work out why my engine is idling very high..(3200rpm)
I have removed the choke linkage
I have checked the butterfly’s which are working how they should ( opening fully- and shutting completely - they are also in sync.
Throttle linkage from the controls is not even touching the the linkage on the carburettors ( so butterfly’s are in the fully closed position)
I have put a brand new switch box in a brand new trigger assy under the flywheel and 3 brand new coils.
And the cold start (ignition advance) is in normal running position….
Starts first pop every time but instantly goes into extreme idle.
Any help would be very appreciated.
Thanks

 

[Nordin]

Check if you have an air leakage around the carbs mounting to the crank case (intake manifold) or at transfer passage cover.

 

[racerone]

Serial # of this motor ?

 

[Vinsta]

Serial # of this motor ?

 

[racerone]

Sounds like timing issues.----Too much advance at idle.-----Did you remove entire flywheel or just the flexplate to replace trigger ?-----You are sure that the splined flywheel is installed correctly ?

 

[Vinsta]

Sounds like timing issues.----Too much advance at idle.-----Did you remove entire flywheel or just the flexplate to replace trigger ?-----You are sure that the splined flywheel is installed correctly ?

Removed entire fly wheel… was the only way to remove the trigger assy. Flywheel spline has a key so it can only be fitted in one position.
When I pull the manual choke out 3/4 the revs die down to about 1800rpm.
I unscrewed the mixture screws to 4 rotations out and archived the same result but its seem to be running to rich

 

[racerone]

Motor slows down with choke because it is flooding.----I do not believe this is a fuel issue.----In my opinion it is a timing issue.