1977 Mercury 850 woes

Hi there all. I am a nautical novice. I was given a 1971 Higgscraft (built here in Austin) with a trailer and title. After a year and almost $1000, i've repaired 4 holes in the bottom, put in new stringers and transom and deck, carpet, seats, and finally, a 1977 Mercury 850. That's an 85hp, if you didn't know. She ran super sweet at first, after a little fuel stabilizer.

Last week I took her out to Mansfield Dam on Lake Travis. She ran well, but I was having considerable trouble with the control box. The forward/reverse lever would not go all the way forward unless I lifted the cold start lever all the way and then set it back down after engaging the motor. Then it would remain stuck in the forward/full throttle position and I would have to turn the boat off and then wiggle the cold start lever back and forth to get the forward/reverse lever to go back to neutral.

I took it the control box apart and saw that the two levers have parts that are either shared or work together. Some of the metal parts in there were stripped out. I put it back together and managed to move the boat most of the way back to the dock, but when we got almost there, the engine died. I managed to get it restarted, and it was just fine and smooth at idle. When I tried to engage the prop, the engine started jumping and shuddering like it was trying to rip the back of the boat off. I had already been having problems with it vibrating a lot at low rpms when you first engage the prop, and reverse had just about quit working. I also felt like perhaps the boat should be moving a lot faster at full throttle. It's only an 85hp, but the boat is extremely small and light (15' fiberglass hull).

Here is what I suspect:

The control box is in need of overhaul/replacement (I know this for sure, but I'm not sure if it's the cause of the engine misbehaving).

The control cables are in need of replacement (I know this too, because they have rust patches and sieze up a bit when it rains).

The lower unit is damaged, or needs fluid? (I'm not even sure if the lower unit has it's own fluid, or what type to add or how to check. I hope its not busted).

The throttle linkage on the powerhead needs to be adjusted? (I was thinking of this for the speed issue).

Carbs in need of adjustment? (One day I found a bolt that had fallen out of the carb laying in a puddle of gas underneath the powerhead cover. I tightened it all the way so it wouldn't fall back out.)

Ignition or fuel problem? (I added some octane booster. I used the recommended amount of 1 oz per gallon for marine engines, but I still felt like the gas looked a little thin. Is it possible the engine got to hot because there was too much viscosity due to the mix being a little thin?)

I'm not sure if it's any or all of these, they probably all need attention anyway, but I'm not made of money. If anyone knows anything that I don't, or has other suggestions, I'd be happy to hear them.

Re: 1977 Mercury 850 woes

Hi!

As a start, I would check out the control box and replace parts where needed. Cables can be greased with MERC grease

Alex

Re: 1977 Mercury 850 woes

ok, here's an update on my situation, in case anyone sees this.

i took the boat to the marine engine tune up class at the local community college. the professor rebuilt my control box and told me to replace my cables. i went to south austin marine and got a pair for $65! i thought i would spend at least $100, but i digress.

now i've got the motor running smoothly at idle, but when i move the throttle/shifter lever forward, the prop seems to almost engage, but will not quite get in gear. i can get it into reverse (thank God, or i'd still be out in the middle of Decker Lake). even if i move the throttle/shifter lever all the way forward, i can not get the prop to quite catch, although it does hit really hard, like it's trying, but falling back out of gear. i'm going to try to adjust the linkage between the shifter cable and the engine, and see if i can get it to engage.

one other note. when i put the earmuffs and start it on land, then shift it into forward, the prop starts to spin like it is in gear. is there a lower unit problem that causes the prop to no be able to create any thrust in the water, even though it is in gear? any thoughts would be greatly appreciated.

Re: 1977 Mercury 850 woes

Most likely spun rubber hub. replace the prop. Well actually the hub can be replaced by a prop rebuilder.

Re: 1977 Mercury 850 woes

With the shift linkage disconnected, you should be able shift by hand between forward, neutral and reverse. There is a "detent" for each, the lever will try to stay in whichever gear. Try to turn the prop with the motor in forward and in reverse to make sure it is engaging. Reconnect the shift after adjusting the length to the middle of the neutral position.

Re: 1977 Mercury 850 woes

Pap, There is a positive neutral detent, but forward and reverse have minimum detent, if any.

Use outboard gear oil to refill the gearcase. Pump it in the bottom hole until it flows out of the top hole.