Mercury 850 Thunderbolt Serial 4102281

[Island_oki2000]

I just traded for this boat and motor. I've been reading the posts and checked the serial and I'm pretty sure it is a 1975. I have a few question to start with.

1. The motor has been sitting a while, I think a year. I had the guy start it and it tokk a little starter fluid and the choke and he got it started. What would you recommend I do before running it again? The motor was peeing good while he had it running for the few minutes.

2. The power tilt and trim clicks when I try to put it up and nothing when I try to put it down...any idea what I can do. I read a post from a guy on a different motor with the same problem and he said he took it apart and cleaned it and now it works fine.

 

[Island_oki2000]

Re: Mercury 850 Thunderbolt Serial 4102281

Also,

The guy I got the boat from didn't remember the fuel oil ratio. Can someone tell me the correct ratio or where to find it?

 

[emckelvy]

Re: Mercury 850 Thunderbolt Serial 4102281

Starter fluid is bad on these motors since most don't have any lubricant in them. Better to carefully spray fuel/oil mix into the carbs.

Maybe the guy didn't know how to start a Merc. You need to pump the primer bulb until it's hard, then a few more pumps for good measure.

Raise the fast idle lever up (with the gearbox in Neutral). Depress and hold the choke button (or push in on the ign switch if the control box is a later style) and crank the engine over until it starts. Be ready to pull the fast idle lever down or turn it off if it revs up too high. Once you start it a few times you'll know how much fast idle it needs.

If that doesn't help, it could be a myriad of things from lean idle mixture to tune-up to worn-out motor. A compression check is probably in order. Of course it's hard to do any water testing if you can't get the motor up and down!

Far as the PT&T goes, sounds like it could be a solenoid. One way to troubleshoot this problem is to "jump" across the solenoid with a set of jumper cables or a stout wire. Be careful of sparks, especially around fuel! If you put power directly to the motor and it doesn't run, you may have luck cleaning it up. Hopefully the brushes/pigtails aren't burnt up, as they are quite expensive. In that case you may have luck taking it to one of the electrical places that rebuild car & marine alternators & starters.

I'm assuming you've got the separately-mounted pump with (4) hoses and hydraulic rams mounted on the motor where the shocks normally go. Later-style with integral PT&T transom bracket uses (2) solenoids and they are almost always the problem.

HTH.........ed

 

[Island_oki2000]

Re: Mercury 850 Thunderbolt Serial 4102281

Thanks for the starting point Ed. By chance do you know what the compression should be? What is the name of the tool used to check the compression. I will have to buy one.

As for the PT&T, I'll need to look tomorrow when it's light, it is mounted under the rear seats and I think you are right about the 4 hoses. I also think it might have had a leak or something because the rear under the seats is full of oil and water mixed. I noticed as I was cleaning it out today. I'll proabably remove the whole thing from underneath and open it up to see if I can clean it up. Is it a pretty hard thing to do to remove it and open it up? Also, looking at the wires and connections, they are very corroded, so I will also need to rewire. I'll probably clip all the wires to get clean connections.

I too was worried about the starter spray. The guy told me he bought it from an older guy who told him never to wind out the starter and to use the spray, so I think he might have been using it all the time. I'm thinking I should take it to a mechanic to have it checked to see what I should do to make it right. Like I said, it only ran for a minute so it never even got warmed up. I wanted him to turn it off just in case there is something wrong and it got worse.

 

[emckelvy]

Re: Mercury 850 Thunderbolt Serial 4102281

Just called a compression gage or compression tester. To get to the bottom cylinder you'll need one with a flexible hose, and may still have to unbolt the cowling supports at the back so you can drop the lower cowling down a bit so you can screw in the hose.

When you do the test, the carbs must be wide open. Easiest to do is have the motor in gear, thottle advanced with the key off. Apply +12V to the terminal on the starter solenoid with the yellow wire attached. Watch out for the turning prop!

Compression should generally be around 120-140 psi, the specific number is not so important as the variance between cylinders. Ideally, they should be even or within 5 psi of each other. As much as 10 psi might be OK but could indicate carbon buildup or piston ring problems. The carbon issue can be handled by use of a decarbonizing agent such as Seafoam but if you have greater than 10 psi diff between cylinders, internal problems are likely.

Here's some good info on decarbonizing an outboard:

http://forums.iboats.com/showthread.php?t=158076&highlight=seafoam

On the PT&T pump, once you unbolt from its mounts you can drag it out a bit to work on.

I dug into my service manual and here's the procedure for testing the motor directly:

Disconnect the black and blue motor leads from the solenoid, then connect (-) battery terminal to the black wire and (+) terminal to the blue wire. If the motor runs your problem is not there. Check the solenoid and control wiring/switches (including the tilt limit switch that should be installed on the transom clamp and visible from the back of the boat when the motor is fully tilted up).

If the motor doesn't run, undo the (2) thru-bolts at the top of the motor and, after match-marking the motor frame to the pump housing, you can pull the end cap, pull the motor armature and frame off the pump. The motor armature's drive shaft goes thru a seal at the top of the pump and engages the pump via a slip-fit.

This is just a simplified description, you'd be well-served by picking up a service manual. Even my lowly Seloc manual has a pretty good breakdown of the pump, and a decent troubleshooting section.

Anyway, that should get you pointed in the right direction, HTH........ed

p.s. Here's a link to parts diagrams for your motor, unfortunately I don't see a PT&T breakdown:

http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=63271

 

[Island_oki2000]

Re: Mercury 850 Thunderbolt Serial 4102281

Ed,

Thanks for the info, I will be using it to try and get this thing in good shape. For the PTT, there are 3 wires coming out of the motor. The black one is bolted to the top and then there are two wires coming out of the motor connected to what I think is the solinoid. One is connected to the side of the solinoid and has a black rubber boot over it. The other connects to something, looks like a black plastic piece that is not connected to the solinoid, it's connected to the top of the pump. I'm guessing the black wire is the ground and the wire connected to the side of the solinoid is the one that should be blue like you explained.

Also, there is a little fuse looking thing, which splits the power wire that connects directly to the battery. It is real corroded but I don't know what it is to get another one.

If you can get me an e-mail address, I can send you some pictures of the PTT. I opened up the oil fill whole and had to turn it upside down for anything to drain out and not much did. I'm thinking it might need oil too.

Thanks,
Kyle