V4 johnson 90hp outboard motor wont reach high revs in gear

[DrewnKate]

hi guys, recently brought the above motor took it out for a test drive and motor will start and idle fine, will engage gears but will only do about 5 knots flat out. If its in neutral can manually maintain high revs using throttle body, so thinking cant be a carby issue.. Any help would be greatly apprieciated

 

[Bosunsmate]

Careful reving in neutral that can blow them up.
You need to check you have spark jumping a 7/16 gap on all cylinders
You could also do a drop test (pulling each plug off with insulated pliers and checking the engine drops a similar rpm per cylinder). That checks that whether every cylinder is pulling a load.
Ive seen these rev up in neutrak with only one cylnder working

 

[DrewnKate]

Thanks for the info will give that a go.