On the muffs: needs LOTS!!!!! of water pressure.
Get a temperature gun and check the temp as it runs and see if it is really getting as hot as it says??
Is the new thermo the right heat range?
Pump installed right?
Here's a pic of the starting system. It should match your starter. Pick the pieces you need??? Then post them and Ill look up the part numbers.
Then you can look on this site or boatsdotnet or ebay to find the pieces..
Probably got the wrong prop for the load.
You can adjust the air screw all day long but if the motors not set up for the boat/load it will always be a slug :(
Pitch of the prop now?? If it's a 9p then go to a 7p
Or contact Michigan Propeller or Solas propeller and give them the specs and they...
Always include the year? Model? Serial#
Like Racer suggested, probably just needs the diaphragm kit.
That too is NLA :(
Found this for you. You should be able to make it work.
857005A1 On ebay 16$
To check the coils: swap them around and see if the spark follows the good coil.
Try Franz marine for the hard to find stuff.
Also Google: Force Outboard Parts Or Chrysler Outboard Parts. That opens a ton of places that sell Force/Chrysler parts.
If the coil tests good?? You can seal it with...
Like Racer said: "MORE INFO" ???
Spark?? Compression numbers?? Fresh gas? Test for water in it??
Anything else?
The more info the better the chance of us answering your questions.
Kinda sounds like water in the gas or the stator maybe a cable not moving??
More info please??? What ignition system? Points or CDI(Magpower)?
Usually an older model needs the flywheel removed and the points cleaned/ filed down.
Pics if possible.?