Mercury 1973 150 hp 1500 top end miss

Anyone have any advice on why my 1973 150hp Mercury inline 6 has a miss at wide open throttle. I know it's old. Rebuilt the carbs, set the timing at about 20 deg.max advance, checked primary pickup at 2-4 degrees and secondary pickup at 20 deg. Primary and secondary have nothing to do with WOT. Seems to idle decent, and accelerate OK, but at WOT it seems to buck every now and then. Compression is about 100psi on all 6 cylinders which is lower than it should be but even. Fuel pumps maybe? Also very hard to start when cold. Fires right up when warm. Any ideas how to improve cold starts?
Thanks for any help. New to outboards. Had I/O's before

Re: Mercury 1500 top end miss

Have you had the distirbutor cap off, is there signs of carbon tracking in the cap or a crack look carefully. check the rotor plate and see if there is any build up of anything on it should be nice and brass looking.

Make sure the wiring from the trigger to the switchbox is good they tend to frey with years. A trigger on that motor will cause a high speed miss but eliminate all the other obvious things first, because they are Expensive.

Do you have any signs of water on the plugs this is always something to keep an eye on with an in-line.

All you settings look fine, you are safe to stay within 2 degrees less than the max spark setting; secondary is set at 20 but is it picking up the carb cluster exactly when you hit max spark.

What Fuel are you running and at what mixture? Do you have a Water Separator filter installed?

On Cold starts, Prime the bulb until you hear a solid WOOSH at the motor then prime once more, put the warm up lever at 1/2 and hold the choke until it kicks or starts, if it spits out the bendix on starting then bring the warm up lever back a little and no more choke that should fire it every time cold and make sure the motor is trimmed all the way down.

Re: Mercury 1500 top end miss

Thanks for getting back. Had the cap off. Cleaned all the contacts and rotor. Looks decent, no cracks. I run 50/1 mix regular gas. Have filter/water seperator. By water on the plugs if you mean outside yes. Have a new water jacket gasket but haven't installed it yet. By trigger, it has the thunderbolt ignition and the trigger is inside the distributor under the cap. Cleaned it as best I could. It is a bear to start cold unless you prime it till gas starts running out of the carbs everywhere. Should be a better way. The miss seems like it's starving for gas but carb fuel levels are as high as possible without overflowing. Was on the river and going with the current and the wind was Ok but going against the current and wind seemed to miss. Strong current and wind.
Again thanks for the advice. Looking for a newer motor.