1998 Evinrude 150 rattle and runs bad only in the water

[Briankpo]

I just bought a 1998 Hydrasport with an Evinrude 150 that has a rattle or knock only in the water and on deceleration. I can't get it to make this noise with muffs on. It will make the noise just revving the engine in neutral which I found out because of the idle/acceleration from idle problem I also have. I'm not sure if they are related or not. It seems to run fine on muffs. In the water when first starting or starting after sitting for about 30 minutes or more it will start right up and then die or want to die. If you try to rev it up it or put it in gear it dies most of the time. Once I can get it to rev up and get going it runs great at high speed and then if I bring it to an idle after going at a high speed it idles fine. Any ideas Thanks Brian

[poolphilter]

I dont know a lot about boats, Im new to them, but I know about engines. Is it carburated? If it is, sounds like your carbs are gummed up. Try by first spraying carb and choke cleaner through the intake while running. If you have injectors, there is probaly something similar for that. I dont know if you have already tried this, but its could be an easy fix. Thats where I would start.

[rebuilt]

Seems to me a compression check is in order. KR

[The-Machinist]

Try by first spraying carb and choke cleaner through the intake while running.

Baaad Idea. Carb cleaner contains no lubricant, and will wash any lube that is on the bearings right off. Also, this does nothing for the carbs towards cleaning them. The only way to clean carbs is disasemble and soak in carb cleaner and blow compressed air through every hole, no matter how tiny.
I highly doubt it is your carbs causing the problem though.

[iwombat]

Does the knock seem like it's coming from under the flywheel at all. Could be a loose fastener on the stator causing it to rub.

If you have a piece of fuel hose, use it as a stethoscope to try and locate the source of the rattle.

[Briankpo]

I think the running problem could be in the carbs. When it dosent want to start I can spray a little carb clean into the carbs (6 of them) and it will start right up and run for a bit. It also seams to be loading up though. I have to get it to rev up and blow it out if you know what I mean. I put some sea foam and octaine booster into the gas tank to try those. Compression: all check between 90 and 105 Thanks Brian

[rebuilt]

Can't overemphasize what themasterofmachines said. NOOOOOOOOOO starting fluid. NOOOOOOOOOOOO running it on carb cleaner. Clean bearings run dry is what you get. Possibly scored walls or worse. If she won't run on a mix, the problem is deeper than what kind of liquid is used to get her to fire. Contrary to shade tree misconception, these motors are a unique mix of mechanical ingenuity. What worked on the ride in the driveway may or may not (probably not) be a good idea to try on your 2 stroker. A seasoned shade tree myself, I had to get re-edumacated.

[Chris1956]

Brian, Is it possible that the noise of the motor when running on the muffs masks the rattle?

Normally a rattle is either a piston slap (no load rev or deceleration) or perhaps a bearing. if it is a bearing, it should occur under load, or all the time. It could also be something loose. My old distributor Merc had a rattle when the distributor pully cover vibrated loose.