1973 mercury 850 carb broken and fixed

bugelingkayaker

Seaman Apprentice
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Nov 13, 2019
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49
So I got a 1973 motor and boat for free last week (awesome!) but it was free because it wasn’t running (not awesome!) and as someone who doesn’t have much mechanical skills but with a basic understanding of how it works I set forth to YouTube to learn as much as I could to see if I could fix this thing. I successfully fixed my lawnmower the other week so how hard could a boat motor be? LOL well Hours and hours of videos later I felt confident enough to start taking it apart. Got everything off and opened up the carburetors to start cleaning them.
All going well until I’m putting the carbs back on. Tightening down a bolt, and tightening, and tightening.... and then suddenly it’s getting looser. Oh no. Oh nononononono please tell me I didn’t just do what I thought I did. Figure ok maybe if it’s just the bolt that broke I can get it out and find a replacement... got it back off and realized nope... I broke the top of the carburetors float cover off.

​​​​​​​After spending a few moments contemplating which cliff I should throw myself off of I decided to look closer at the damage and saw some promising news: 1 the break was well above the first inlet so it’s only the part the bolt goes into that broke. 2: it was a clean break. So maayyybeee all is not lost. Checked online to confirm my fears that the part is not available anymore. So fixing it was my only hope. Tried roughing up the sides and then carefully applying some jbweld around the break and letting it sit. And while it seems to be holding I don’t want to take the chance of it popping free from the force of all 85 stallions in full gallop 5 miles out to sea. So I hit the workbench and cut out a couple pieces of steel, some pieces of gasket material and created this little bracket assembly. The part that had initially broke was to hold the little bell thing down against the rest of the carb, so to avoid stressing that too much, my bracket just goes around the whole side of the carb gently but firmly pressing it together.
anyways, as a non mechanic, how do y’all think I did here, am I a genius for finding a workaround? Or a moron for breaking it in the first place (I agree :( ) and then for thinking this might work?
anyways, words of praise, criticism, advice, all welcome. Thanks y’all
 

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racerone

Supreme Mariner
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Dec 28, 2013
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That part was used for many years.-----Dime a dozen for used ones in some areas of the country.
 

Chris1956

Supreme Mariner
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Mar 25, 2004
Messages
28,074
As long as it doesn't leak fuel out or air in, it should work. However, those carbs were used for many years. A new (used) carb cover should be pretty easy to find. They come in the style you have plus a newer "back drag" style as well.

Your motor should have a distributor with battery powered CDI ignition. Inspect the wiring harness as they tend to be bad by this point in time, if not replaced. Also, the distributor rotor is not removable, and very fragile. The distributor cap usually doesn't need replacement, but if it does it is $100+. Coils are cheap, but usually don't break.

Switchboxes are $200+. Replacement rotor+ shafts are $225+ and a PIA to install.

I would recommend a Mercury service manual, rather than U tube videos.

Best of luck.
 

jimmbo

Supreme Mariner
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May 24, 2004
Messages
13,638
I doubt it would pass a USCG inspection. Being only clamped/cinched on one side is an Accident waiting to happen. As previously mentioned, those parts are very common. Most dealers have more than a few of them littering the Back 40
 

bugelingkayaker

Seaman Apprentice
Joined
Nov 13, 2019
Messages
49
Thanks for the responses! The pics don’t show it well but the bracket I made does have bolts going on either side of the carb so the the pressure is even across it.

any tips on how to test the distributor for what you are talking about? I have a multimeter but I’m not sure what I would be testing for exactly. I am getting good spark from the plugs so hopefully the electrical stuff is all good.
I tried doing a compression test, on the top 3 cylinders the results were: 92, 89,88, and unfortunately the 4th is such a pain to reach I couldn’t get the gauge down to reach it.
Assuming it’s close to the others do you think this motor is worth spending time and money on getting it running well? I was expecting higher compression as most things I’ve seen online show 120+ but I figure it’s promising that they are all so close in range. I figure i probably won’t be getting 85hp out of this thing but that’s not a deal breaker for me if it will still run well and last me a long time
 

The Force power

Commander
Joined
Feb 3, 2019
Messages
2,350
Thanks for the responses!
I tried doing a compression test, on the top 3 cylinders the results were: 92, 89,88, and unfortunately the 4th is such a pain to reach I couldn’t get the gauge down to reach it.
Assuming it’s close to the others do you think this motor is worth spending time and money on getting it running well? I was expecting higher compression as most things I’ve seen online show 120+ but I figure it’s promising that they are all so close in range. I figure i probably won’t be getting 85hp out of this thing but that’s not a deal breaker for me if it will still run well and last me a long time

Don't assume the forth cyl. is the same reading! & your numbers are too low maybe check with a different gauge?
IF.... these numbers are true, it will never run "well" (on a hose or in a bucket yes, on the lake no)
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,074
I installed a brass tee on my compression gauge to reach the bottom cylinder.

A lot of compression gauges are inaccurate, but most are reliable. That is if they show close compression across all cylinders, the motor has even compression. Even compression is real good, and usually indicate a good motor.

The CDI electronics web site has a test for your ignition system, or at least for all components but the trigger. I recommend you perform it.
 

The Force power

Commander
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Feb 3, 2019
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2,350
I recommend a liquid-filled gauge as the needle cannot bounce and is not easily get thrown out of wack by rough handling
a flex hose attached to the gauge can be helpful
 

bugelingkayaker

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Nov 13, 2019
Messages
49
Good news! Harbor freight compression gauges are 💩💩💩 took it to a nearby boat shop Because they offered to let me borrow their gauge to retest and try and reach the bottom cylinder. Their gauge read:
cyl 1: 140
cyl 2 141
cyl 3 132
cyl 4: 139
so I guess I’m in a lot better shape than I originally thought 🙌🙌🙌
 

The Force power

Commander
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Feb 3, 2019
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That's great news! those are pressure you'd like to see, once you have it running & some carbon cleaning; the lower numbers might come up.

you're off to the next phase
 

bugelingkayaker

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Nov 13, 2019
Messages
49
So the carb seems to be holding together fine so that’s good, but to be on the safe side id still like to replace that float cover. A couple of you mentioned that I should be able to find the part used somewhere. I’m new to boat motors though so I’m not really sure where to start looking. Should I just call around boat shops and see if they happen to have one laying around, or are there any sites in particular that are good for finding cheap used outboard parts?
 

The Force power

Commander
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Feb 3, 2019
Messages
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Marketplace/Ebay/local sources look for it
sometimes you can find a donor motor cheaper then the part(s) you're looking for
 
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