1986 Mercury 900, running then wont start...

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Insaneplmr

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Feb 1, 2011
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Good morning and Happy New Year,

I bought a used Mako 19 center console with a mercury 900 on it. It ran with the muffs when purchased, and then again before I took it out this last sunday. Put it in the water, started right up, got out of the marina, came up on plane real nice and quick, held it there for a minute or two and as I backed out before the shallows at the channel, it died. I could not get it started again. after a quick tow by the local sherif (thank you) I got it home.

Did compression check, although low numbers(#125 I think it should be higher) in all cylinders they were within 2 psi of each other, I checked for spark but only in one cylinder, had spark. I checked the vent on the tank, checked for clogged fuel filters, can pump gas with bulb to the point where it dumps out the throat of the carbs. still no start. while cranking a small shot of starting fluid by the carbs will get it to fire off for a sec.

Will be trying to play with it some more today, had to recharge the batteries after all this cranking. Also if someone could explain to me the wiring configuration to the controls that would be nice, I found a diagram with the color codes but I still don't know what all they are for and its a rats nest under the console.

Thank you for any ideas,
B
 
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Maxz695

Guest
Re: 1986 Mercury 900, running then wont start...

125 PSI on all cylinders within 2 psi is fine. Having spark on on cylinder shows you may have a bad switchbox but testing will have to be done to assure you this is the case. Other issues like a bad trigger wires plugs coil grounds connections to the switchbox or if distributor modle engine It could be cap rotor wire etc etc. There are online manuals in the sticky notes that can assist you in trouble shooting the electrical system. Boatinfo - The library, containing manuals, brochures and other technical documents from the last hundred years!
 
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Insaneplmr

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Re: 1986 Mercury 900, running then wont start...

Thank you for responding,

I looked through that section that you linked me to last night. I could not find my particular model or serial number. it seams that all the manuals cover 1987 and up. It is possible that I overlooked it as there are 6 or 7 books for a 90hp. The serial number is# A902602, appears to be a Canadian model 1986. Inline 6cyl no distributer, just coil boxes.

I will check for spark in the other cylinders today after the neighborhood wakes up. I only checked for spark in one cyl assuming there would be spark in the others.
 
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carholme

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Insaneplmr

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Re: 1986 Mercury 900, running then wont start...

Thank you Gerry,

I will have to wait until payday for the manual on ebay. I appreciate the parts list and the link, it is downloaded and printing as I type.

Brett
 
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Insaneplmr

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Re: 1986 Mercury 900, running then wont start...

So I went this morning, pumped the ball until hard ant then a little extra, pushed the key down for a five second count and cranked. after two false starts and a repeat of the bulb pump it started and ran at idle for a good 15 min. shut it down and it fired right back up. One of the neighbors informed me that they are super cold blooded and to let them warm up at dock for a good five to ten minutes.

So my question is if it died because it was run to hard while cold and shut down on its own after backing off the throttle why could I not get it started again? Are these motors easy to flood? or just seriously temperamental...lol.
 
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narvlebenoit

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Nov 22, 2009
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Re: 1986 Mercury 900, running then wont start...

I have one just like it very hard to flood them check all your gas lines to make sure you dont have any air leaks and yes they are cold hearted motors.
 
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Insaneplmr

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Re: 1986 Mercury 900, running then wont start...

I checked the gas lines, they appear to be ok. instead of hose clamps they have zip ties. is this normal?
 
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carholme

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Re: 1986 Mercury 900, running then wont start...

If you look at item 23 under FUEL PUMP AND FUEL LINES (NEW STYLE FUEL PUMP), you will see that they are quite normal. You always have to be sure that they are the marine straps which circle the tubing completely as opposed to the normal tie straps which when tightened will bunch up the tubing causing a possible air/fuel ingestion/leak.

Gerry
 
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Maxz695

Guest
Re: 1986 Mercury 900, running then wont start...

proper mixture screw setting are essential to get the engine running on a cold start and having it just right for a good clean holeshot. I think if you take it out and experiment with the carb mixture adjustments it should get better. It may be running either too rich or too lean to cold start. Best thing to do is close all mixture screws to a light seat. then back out 1 1/2 turns. (Do this for all carbs).Start the engine. Now starting with the lowest carb turn the mixture screw in until you hear it start to stumble. At this point turn it out 1/4 turn. (Do this to all carbs working your way to the top carb). Now take it out leaving mixture screws accesible for fine tuning. Try gunning the throttle. If it picks up and goes like hell then it should be good. if it falls on it,s face then bring all carb mixtue screws out 1/8 of a turn and try again. Repeat until a good clean solid holeshot is aquired. This should bring the low idle jets to an acceptable adjustment for the best starting mixture when cold. Remember to choke after priming the bulb until she wants to start then increase the Hi idle lever and turn it over with no choke. run a few seconds then bring it down to a complete idol good luck.
 
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Insaneplmr

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Re: 1986 Mercury 900, running then wont start...

Maxz695 said:
Remember to choke after priming the bulb until she wants to start then increase the Hi idle lever and turn it over with no choke. run a few seconds then bring it down to a complete idol good luck.
Click to expand...

I will do that on sunday if I get time to go out on the water. Unfortunately the controls are not for the motor, I don't have the hi idle lever, nor does it have the ability to rev up in neutral, only in gear. It also doesn't have a neutral safety switch so I really need to look into mercury controls for a center console.

The choke assembly appears to be missing as well. It typically doesn't get below 40deg so having a choke would be nice but untill I find out whats missing I will have to do without.

Thanks for you help today guys!
Brett
 
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Mi duckdown

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Apr 14, 2007
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2,575
Re: 1986 Mercury 900, running then wont start...

You need choke. what ever the temp IS.
 
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