Merc 850 Thunderbolt

[Bluewater84]

Hey There!

I have recently purchased a 15ft Glastron T-172 Beau Jack with an 850 Thunderbolt ignition merc on it. I got it for a steal and the lady I got it from said her husband ran it all the way until 2015 when he passed away. The motor looks to be in factory condition. Photos to follow.

My my question is what to initially look for. The red battery terminal is shot and will need to be replaced for I can even check trim and other electrical settings. I plan on running some fresh fuel to see what kind of “kick” I get off of the initial start. I figure since it’s sat for 3 years I’ll need to clean the carbs.

This is is my first “big” motor. I’m used to 25hp and lower outboards so any guidance would be much appreciated. I’m pretty mechanically savvy but I know marine can be a ***** if you’re not experienced.
Thanks in advance!!

 

[Bluewater84]

It says my pics are too big to upload. Any suggestions?

 

[Bluewater84]

Sorry the serial number is 4596628

 

[Chris1956]

The serial number indicates that it is a 1977 model. If so, it will have the modern ADI ignition system with 4 coils, which is good.

I would check/clean all wiring connections, with the battery disconnected, one at a time, so you cannot mix them up.

Change the gear oil and grease the motor swivel, tilt and steering.

Next take a compression reading and spark test. There is a sticky about awaking a sleeping outboard. You might read it.

You will obviously want to mix up some fresh 50::1 fuel. Regular unleaded gas and TCW-III oil is recommended.

Connect a flusher to it and see if she will run. To cold start, cold start lever all the way up, pump primer bulb firm, hold choke button down and crank her until she fires. If she won't idle well with the new fuel, she likely needs carb cleaning.

 

[Bluewater84]

Wow thanks! I had planned on doing most of that but didn’t think about the connections. One question. You talk about cold start lever. Where is this located? Is it the lever that is between the hull and the accelerator? I found it last night but wasn’t sure what the lever was for.

 

[Mercurylips]

Blue- Make a concerted effort to check the wiring (interior and exterior) on that motor for degrading insulation. Those year classes are notorious. I have a 77 Merc 500 and all of my wiring has now been replaced. Suggest you get a Mercury Service Manual for it and keep coming back for help when you need it.

 

[Bluewater84]

I’m glad you brought that up Lips. Any ideas where I might be able to find a manual for this model?

 

[Mercurylips]

I found one on a famous website that rhymes with day. I did some checking and sampling and found the Mercury Service manual to be a bit easier to interpret. Cost was not prohibitive.

 

[Bluewater84]

Found one. Thanks!

 

[Bluewater84]

So I got to looking in the rear well where the battery and gas tank are. I have found 2 sets of black battery cable terminals. One is coming from the motor and the other one is coming from up near the throttle. My question is what is the one coming from the throttle? Is that the electrical hookup for the power trim? Thanks!

 

[Mercurylips]

That could be from a few things, not sure. It may be for a front mount trolling motor that someone rigged up "their way".

 

[Bluewater84]

There is a foot pedal Minn Kota on the front of the boat. I’m sure that’s it then. I just got the new cable and new fuel lines tonight. Gonna hook it up tomorrow and give it a few turns and check all of the electrical. I’ll post and update then.

 

[Bluewater84]

Ok. So I got the battery cable and fuel lines replaced. Fresh gas. Went to fire it up and all I get is a “click” when I turn the key on. And click when I let off of the key. I’m assuming it’s the starter? But I’m not 100% percent sure if I’m missing anything or if there is anyway to bypass this. Thanks!

 

[Mercurylips]

Hope the pros are reading this. You need more help than I can give you. Could be your solenoid but it also could mean a poor connection or weak battery.

 

[racerone]

Key has 3 positions ---engine off ( not running )----engine on ( running ) and engine cranking to make it run..-----When you turn key to " on " there should be no " click " at all.-----Electrical problems can be difficult to explain / trace.----Therefor you need to be very clear in questions / explanations as to what is happening.

 

[Bluewater84]

My apologies Racer. Thank you for the clarification. The clicking begins when I turn the key to crank the motor.

 

[Bluewater84]

Merclips, I thought the same thing. While looking in the motor I’ve found the starter cable is exposed and in bad shape. I also thought replacing a solenoid at first would at least give me peace of mind knowing I had a new solenoid on it. Anyone know the correct usage of a multimeter on this to tell if I’m getting the correct amps/voltage to each part?

 

[racerone]

Some will argue----I would take the starter apart for inspection.---An ohm check from commutator to the shaft should show infinity.---That inspection costs no coins !

 

[Bluewater84]

Commutator to shaft? Can you elaborate? I’m not familiar. Or maybe a link that explains? Thanks for the help!

 

[Chris1956]

You can jump the starter directly from the battery, bypassing the solenoid, key switch and the quick disconnect plug. These can and do get dirty or fail.

Mercury starters are mounted in rubber, so they need a ground cable. It will run from a bolt on the top of the starter to the upper cowling support. Make sure yours is clean and sound.

Next jumper the starter to the battery, bypassing the rest of the ignition system. To do that connect a jumper cable from the battery + terminal to the lower connection on the starter. The motor should crank. She will not start, unless the ign key is in the run position.