Somehow I doubt the motor had 150 psi when it left the factory floor but maybe....a used motor should not test to 150. Something feels wrong with your test.
That being said, sounds like you have crud in your head. Remove head and check. Someone knew it had a problem and tried fixing it by...
50 to 1 will be 16 ounces per 6 gallons of gas not what was mentioned before.
Also, just like Racerone recommended, compression test. It will give you indications if you have internal damage
Pull this fitting off the block and start it up and see if water squirts out....I've scene them plug behind it.
Also, buy an IR gun and shoot the head and see if it's overheating.
When checking for spark and doing compression checks your coils need to be grounded otherwise you are putting extreme pressure on them.
I'm also assuming you have checked all grounds.
Here's my 1985 right after I put a new fuel pump in it ...there's a service bulletin on my year to run the timing up 1/4 to 1/2 past the marks before the carbs open when doing the linc and sync....used to cough at going from idle to wot.
Just because it pumps water doesn't mean it's flowing around the engine. Sounds like an overheat...do not run this motor until you find out what's wrong. These are easy motors to work on.
On the 40 I think it's an 87 or 84... L being the model year designation.
The 50 must be a TLHU but I'm trying to get that verified....which I think equates to a 1996
Trying to verify years here..... Not sure why Yamaha makes it so tough. The 50 HP on the tag says 6h5L590258. 50ILHU and he was told 1996
The 40 has these tags and he thought it was an 1994. Looks like a 1984 to me, anyone know?
