Re: 1990 Johnson 90hp outboard...need advice
In the long term, some honest advice may prevent the next motor from going the same way this one went. These things need some maintenance in order to keep working without blowing up. I had a feeling advice wouldn't be taken as such and you'd be insulted and I'd get slammed.
I have owned about the same motor as you have now (slightly older) and there is nothing wrong with them design-wise, other than them sucking down too much gas for the V4's. Fixed a bunch of them too.
The block is probably trashed, but that won't be known until it is inspected. I don't see how the mechanic can give you a good price without at least taking off the LU and head, but he is probably just quoting you the price to switch out the block with a rebuilt one. It's smarter for him to do that, as that would be guaranteed to work and he could work a long time on yours and it still might not work.
Some things to keep an eye on next time:
Check the gear oil occasionally for water intrusion. A piece of fishing line at the beginning of the season will ruin the seals and there will be water in there for the rest of the season and the gearcase will lock up.
Pull the spark plugs every now and then and check the color. This will show if a cylinder is having problems.
Keep a close eye on the VRO oil level (if equipped) to make sure it is actually pumping oil. I do know some paranoid folks that have VRO systems that still premix at 100:1 "just in case".
Check for water flow out of the tell-tale a couple of times during the day to make sure it's pumping water.
Listen to the motor and trust your gut. If it sounds "off" then something is wrong and fix it. With a multi-carb system, it is real easy for one carb to get clogged and run lean. This will destroy a cylinder, but it will not be running quite right before this happens.
Get a good fuel-water separator. This will keep the trash out of the carbs.
If you look at my 4000-odd posts, you would see that I go out of my way for hours pretty much every day to help people with their J/E motors and am happy to help anybody. I've been working on these stupid things for about 35 years, some of that in a marina/ repair business and I think it is a good thing to spread some of this knowledge around. There are guys like Frank (F_R) and boobie that have been at it even longer.
On the brighter side, there is a chance that there is just a broken connecting rod that didn't take out the crank and cylinder, or that the lower unit is locked up. Take 'er apart! You've got nothing to lose at all and it's kind of fun taking this stuff apart.
