1978 mercury 900 starting issues (90hp outboard, tower of power.)

[terry kozmo]

Hello and help, Koz here, I need some help figuring out whats up with this motor. I had a running motor, and one day, is seemed to run like it was getting no power on take off, at an idle ran great, I hear all this "ticking noise" sounded like plug wires bad.. so I got it home. and figured I'd get new 7mm plug wires and replace them (had to put them together, screw ends, and all). Got that done and put cap back on. In this process, I made note off a lot of the "common" bad wiring insulation falling off on some of the motor wires. So I proceeded to replace those wires and ends, tried to match the correct wire sizes. Now I can not get it to start, it has spark at all plugs, removed the fuel line from top of fuel pump, and getting fuel to the carbs. but it just wares the battery down trying to start, choke works, and I tried the manual 'link & sink", and still nothing. If I spray starting fluid in carbs, it seems like it try's to start, but briefly, and shakes real bad.
Thinking Many things could be wrong here. Questions, could the spark be two low? do to improper wire size (7mm, should be 8mm wires?) they look correct size, wire core wires. Could I have used wrong wires in the wire replacement areas? I have spark at the plugs? Could this be a faulty trigger? I even ordered a new coil that I am waiting on to try, but I have spark? any help here, I am very lost... This motor ran great until that one day when I lost power and it sounded like ticking plug wires when given gas. I have been unable to start it since I replaced the wires........

 

[Boomyal]

I think you need to post this question in the Mercury outboard forum. You'll get many more knowledgeable responses there,

 

[southkogs]

Moved it for ya'.

Welcome aboard.

 

[terry kozmo]

thank you, I am new in this and don't quite understand this forum page, now I have to find it here..... .

 

[Chris1956]

The OEM spark plug wires were stranded stainless steel. Replacements must be solid wire, stainless is best, but copper will work. Are the plug wires on the right spark plugs? The cap should only fit one way, as it is keyed. Make sure that is correct, and the cylinder numbers should be cast into the cap as well.

 

[terry kozmo]

Yes they are solid wire core (I believe copper strands), and I made sure they are on the correct cylinders, and the cap would only go one way (keyed cap with little movement). Are 7mm plug wires correct size for this application? I am getting spark at all plugs, wondering if its fuel to the cylinders?, I am getting fuel thru the pump up to the carbs. Its funny, I do not like using starting fluid, but when i give the cards a squirt, it will fire for a sec, ruff shakes, but fires? back fired once and caught the excess gas on fire, (quickly put out), could this be a trigger problem? what's weird is it ran ok and started fine before I replaced new spark plug wires, and repaired some bad engine wires, (before this, I just started getting this ticking (like spark plug sparking noise at exceleration, and lost power). (It sounded just like the ticking you got when you turned it over with a plug wire off plug, times many) now messing around with it, I may have the timing off, tried to link and sink, seems to be close. but I never removed the timing belt, or flywheel, or distributor. I have a timing light, but can't get it to fire to use it....

 

[Chris1956]

Well, you need to determine if you have spark at all plugs. If not, you need to troubleshoot the ignition.

The coil wire to the dist. cap unscrews from the cap. It pulls out of the coil. I would put the timing light on it and crank the motor and see if she fires 6 times/revolution. If so, maybe the spark plug wires are not made correctly. You can buy OEM replacement wires on the web for $6/$7 each. Look for "Yellow Tiger Tails". They will come with the screw terminals, and you can install the boots.

 

[terry kozmo]

Thanks, I will try the timing light this weekend, but I pulled all the plug wires, and had spark at each plug.

 

[terry kozmo]

Question here, Is the 7mm plug wires ok? what was on there from the factory?, were they 8mm? I no longer have the old wires........

 

[Chris1956]

If they don't arc under high load, they are fine. If they arc, they are NG.

 

[terry kozmo]

I believe no arc on them, they do give spark to the plugs..... The arc I assume would be around the outside of the wires ?...... , Chris thank you for your input here, I am soooo baffled by this whole thing.... I am now to the point of replacing a lot of probably unnecessary items, ordered new coil, and carb rebuild kits, This motor in its life has never had these things replaced or repaired. Figured it can't hurt, But still not really sure the problem, this boat ran good for over a year and one day it at throttle gave me this strange spark knocking and loss of power, but at idle it was fine, and would restart right back up when shut off. I did replace the gas tank when I first got the boat with a alum tank so I would not have fuel problems, before I even started the motor after sitting for many years. I just wish this was more uncomplicated that it is, and maybe it is? something simple that I am missing, But after many starting attempts, nothing. no fire, but it will hit on starting fluid. So process of elimination tells me no fuel getting to the carbs?, But what does this have to do with me replacing the plug wires? It started fine before all this wiring replace and repairs. I feel the plug wires are fine now, I have spark? I will check that timing this weekend with the timing light and see where that takes me. And maybe find a way to check the control unit to see if 12v there where needed. I'll trace all the wiring on motor to make sure power is there were needed. I hope this weekend I find some answers.....Again Thank you Chris, I sure am leaning a lot about the "tower of power".

 

[Chris1956]

If she runs for a few seconds on starting fluid, or better yet gas/oil fuel sprayed into carb, then the carb is likely clogged. If she won't start w/o starting fluid, but then runs after starting, you are either not choking it enough, or the motor is not cranking fast enough or both.

If the carbs have never been cleaned, and she sat for a while, it is likely the carbs are clogged. You will want to disassemble, clean all passages and reassemble with new floats, inlet needle and seats and gaskets.

There are some pinhole-sized air passages in the carb throat, on the bowl side. These are part of the idle circuit. Make sure they are clear.

 

[terry kozmo]

ok Chris, exciting news, (I think?). I pulled the coil, and its cracked.....pretty good crack, now that would explain the spark like ticking noise we last heard when running, and maybe why it would idle ok then.... could this be my whole issue???? probably didn't need those plug wires....... I have a new coil, but it looks like its a little different in the base area. The old one fit into a round metal like half moon, with a rubber seal around it. This replacement part # from pro marine is #18-5186, or 339-832757a4, it looks the same except for the bottom is not round like the old one. And I need to use the metal brkt to mount this new coil. There is a rubber bottom seal also on the old coil, Is that needed on the new coil? just wondering if you knew this before I call manufacture of the new part. GOD I hope this is the HOLE problem.? Although I may have some adjustments to now fix from dinking with all the other stuff..... not putting new coil back in boat until I make sure it will work....thanks again, and feeling good if this is it.......

 

[Chris1956]

A cracked coil would arc to the metal cover I would think. The coil you provided (18-5186 )looks to be the correct one, and should fit into the metal cover you have. I would not worry about the rubber seal, it was probably to reduce vibration.

 

[terry kozmo]

update, ok I now have awesome spark (replaced coil), and did the link and sink, but after a starting attempt, no fuel getting to the plugs, the squeeze ball seems to stay hard, I now wonder if I have plugged carb inlet, I am getting fuel past the fuel pump. Any idea here? could this have anything to do with timing, link and sink? I have carb rebuild kits, should I attempt to rebuild the upper carb first? help.......

 

[rcwannab]

I'll be watching this thread as I recently acquired a 1979 90 hp that will fire if premixed fuel is sprayed in cylinder but nothing else after a full fuel pump and carb rebuild. I can manually choke(cover with my hand) and have hand full of fuel.

 

[terry kozmo]

ok , still had trouble starting, and got great spark now, I took the top carb off, and took it apart and cleaned and replaced the float needle and seat, got it to start and idle, (happiness), so I now know I may have had carb issues, I took and dropped in the lake, Hard start, but did, had good idle, and good take off, I haven't even made any ajustments yet and got it to take off quick and full throttle. , When crusing across the lake full throttle, I Iooked back at the motor, and the center carb was pushing a lot of fuel out the front, bad, I never seen any thing like this, I shut it down, and now think I may need to rebuild the other two carbs also. I may have the float needle stuck on that carb... and or, maybe the plastic lever from top carb , to the middle one is off adjustment, I wonder if that may be it... back to drawing board, but it will now start, I think its now down to adjustments,,, carb issues.....

 

[terry kozmo]

Update, going to remove the other two carbs this weekend, and replace floats, and needles and seats and clean, hope this solves this heavy gas flow out the center carb issue, I am confused about this, I have never seen this on anything before, it was like gas just pouring out the neck of center carb at high speed, wow. What adjustment would cause this?, Is it maybe because the plastic lever from the upper carb to second carb is off adjustment? I wonder here, I will know this weekend I hope.... I will check the idle air holes on the carbs make sure they are not plugged.... Carb idle adjustments still need to be made also, I have the screws at 1 3/4 turns out now.. (I have to admit, I have learned a lot working on this thing.......

 

[Chris1956]

Well, it does sound like your carbs need attention. Replacement of floats is a standard maintenance item as the original floats were foam and alcohol in gasoline disolves them. Replacements are hard plastic and they can crack. Inlet needles and seats just wear out. New gaskets are real cheap, so replace those as well.

Set the carb float height and drop to factory specs as well. Initial idle mixture screw settings is 1-1/2 turns open, They will likely need to be abit more open to allow smooth acceleration.

 

[CV16]

If you run that reformulated gas, I'd replace all of the fuel lines with new. The old ones were not made for the new gas.