[lookingforluck]

I have gotten a Mariner Magnum III 150 and have another post about it with the 70# compression. I did the decarb and gained five pounds of pressure but now it is hard to start, I have to let it turn over a good 7 or 8 seconds before it will hit. I think it made it worse. Any suggestions? It will start right up after that if you let it idle for 10 seconds.

[WillyBWright]

You need to address the 70# compression before you do anything else. I'd pull the heads and see why. When it gets that low, it doesn't pull gas into the cylinder. The gas carries the lubrication, so it won't get lubricated and will get worse til the pistons disentegrate, destroying the block which might still be salvagable at this point. If you keep running it, it'll be scrap soon.

But first let's address your compression testing. I let the motor spin with a helathy battery with all the sparkplugs out til each cylinder has 7 to 9 strokes. You can count them by sound, it happens in 2-3 seconds. I also try to watch the gauge as I'm testing. It should reach peak compression around the fifth stroke. It's also possible that your compression gauge is inaccurate. It would be odd for all cylinders to be equally bad. You usually get a few good ones and one or more bad ones. If all six are reading 70-75#, I'd be looking into trying with another tester, or try the tester on a known healthy motor.

When compression gets low, the pistons have a hard time pulling fuel into the cylinders. If that's the case, it'll be hard to impossible to start.

Let's also go over the starting procedure...
Pump the primer bulb til firm.
Give it a little throttle
(with the warm-up lever on remotes with the key in back, or by pushing in the button in the center of the radius, or pulling out the lever whichever the case may be, and engaging Throttle-Only mode on remotes built into the side and key on the dash).
Push the key in as you turn the key to Start and keep pushing til the motor starts.

Don't keep holding it in once it starts, but you might have to give it a few quick pushes to keep it going for the first several seconds.

If that's an EFI, give it no throttle and pushing the key does nothing. You might have to give it some throttle, but try without first.

[lookingforluck]

something has happened to my boat that when you hold the key in and try to start, it does nothing. I turn it to on push in and hear the choke click, turn it again with the choke pushed in and nothing happens until I let out on it and then the motor turns over.???

[WillyBWright]

Then your problem is probably the key switch. You have to be able to choke while cranking.

[lookingforluck]

Where do you get one?

[gss036]

(Where do you get one?) I assume you mean an ignition switch? Firast I would try starting w/o the cowling, there is a small button on top of the enrichner, turn you key on and push on it, then try starting w/the key. That should have put fuel into the carbs. Otherwise spray fuel into the nouth of the carbs from a spray bottle. An old blow torch can works great if you had one, less dangerous than plastic.
But, until you get the compression issue resolved, I think you are spinning your wheels, as indicated above. Advise is only helpful if you use it.

[lookingforluck]

I am going to get another compression tester to double check myself. I can't believe that is right because it wouldn't be starting and running very good with that compression. If the new readings are 100 or above, then what might my problem be? I tried the turning of the flywheel and holding my finger over the spark plug and it would blow my finger off, just barely. I didn't hear the air really escaping anywhere except the other plugs.