1973 Mercury 850 Thunderbolt is possesed...PLEASE HELP!!!

TenE3072

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Mar 15, 2011
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This motor has been a nightmare, but I wont let it win and all I want to do is take it to the lake. I bought the 1970 starcraft supersport with the 1973 Mercury 850 thunderbolt a couple months ago and have not been on the water yet. My days are limited here in Wyoming before it is time to winterize it. My first problem was when I got it home and was testing to see if it would start. My neighbor came over and was talking to me about the new project. It started fine then died. I was talking to him and he looks over my shoulder and said "your motor is smoking". I turn around and noticed smoke was coming from the CDI ignition pack. On further inspection it got so hot it was dripping plastic. I found it had some bad sheathing on the positive and negative wires under the splash well that were touching, I then electrical taped the wires. So then I get a used OEM ignition pack from a boat graveyard here. It starts up fine and I think it is good to go to the lake. Then it wont start sometimes and I started moving wires when it is running and found a bad boat to motor wire plug that had an issue. So I hard wired the motor and it started and I thought again I could go to the lake. Not so fast... It then starts to randomly start and not start. I found a worn carbon pin in the distributor cap and replaced that. Still starts and wont start randomly. I do the Ignition pack test many times when it wont start and I get spark every time I test it. So I go back to the boat graveyard and get a used trigger and it started so I thought it is time to finally take it to the lake. Not again but it sometimes wont start. It is a spark issue because when it does get spark it fires off instantly with the key engaged. It runs and sounds perfect when and if it starts. It has gone as many as three days of starting about 5 times a day without any issues and as few as ten minutes between starts to not start. The last two days it wont start at 9 am then starts instantly at noon and will start the rest of the day until the next day. Sure seems like once it gets spark it it good for the rest of the day. When it wont start I have tried moving wires with no success. I had my neighbor checking volts when cranking and dont remember the numbers but they seemed good. On the ignition pack the red wire always has power and the white wire has power with the key on. Any help would be appreciated! I have already spent the money to register the boat and I am too worried to drive to the lake just in case it wont start. All this makes no sense. I can do nothing to it when it wont start and next time i go try it, it fires right up...
 

gm280

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Jun 26, 2011
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TenE3072, :welcome: to iboats...

I read you thread and have a question. Does it seem like every time it won't start the temps are cool? You kind of alluded to that possibility with the " it wont start at 9 am then starts instantly at noon and will start the rest of the day until the next day". Sound like there could be a temp issue when it is cold. I would check the key switch like SoCalBoatGuy suggested above AND remove and clean every electrical connection on the engine. You can't look at a connection and tell it is good or bad. But you can remove the connections and clean them to clean shiny metal again and reattach. And make sure you clean the ground wire at the battery and engine. Amazing how many iffy engine problems turn out to be the ground wire. JMHO
 

TenE3072

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Mar 15, 2011
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Thank you for the responses! It seems like it that last few days it wont start when cool. It is Wyoming and last nights temps only got down to 50. That is pretty warm for this time of year. If I can think back I am almost positive I have started it on colder days. It has just had the 9 and noon thing the last few days. I will look at all the connections again and take apart the mercontrol and see if the ignition looks weird. Thanks again!
 

Chris1956

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Mar 25, 2004
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First check your battery cables, their whole length to make sure they are good. Next Jumper the ignition to remove issue of intermittent wiring. To do that run a jumper wire from the power wire on the starter solenoid to the red wire on the switchbox. Next jumper the red wire on the switchbox to the adjacent white wire. That removes all the rest of the ignition wiring from the circuit. Now see if the spark is steady.
 

TenE3072

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Mar 15, 2011
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I dont even know where to start... This darn motor is getting the best of me! I am still having the same problem of not starting when its colder in the morning. At the end of last year I took it camping with me and it ran when first out on the water. Then started running worse and sputtering. It was getting late and decided to beach it. For the next three days of camping I tried starting it around 20 times a day with no success. I was so frustrated I didnt touch it for a month until I was going to winterize it. I turned the key and it started right up... So this summer I got a new ignition and ran all new battery cables and ignition wires. Then the motor fired up. I thought I had it fixed. Nope the next morning at 9 it would not start and started right up at noon again... So went back to the motor graveyard and tried different switchboxes. After two bad boxes I found one that worked and it started the motor all afternoon, about 6 different times with many starts and restarts. This morning at 9 with hopes high that I fixed the problem I went to start it and cranked it for about 2 minutes and not a single sputter out of it. CRAP NOT AGAIN!

So far I have tried:
New Ignition switch
New battery cables and ignition wires
2 different switch boxes
2 different triggers
New carbon pin in distributor
New Spark plugs

I am tempted to try an Ice pack on the ignition components one at a time in the afternoon to see if it gives me a no start when it is warmer.
Any other suggestions would be greatly appreciated!
 

TenE3072

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Mar 15, 2011
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Went home for lunch at noon today and the motor fired right up like it is supposed to. This seems to me a little more than cold blooded. I am afraid to take it to the lake because our waters here in Wyoming are always COLD!
 

TenE3072

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Mar 15, 2011
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I go turn on the water to muffs. Open gas cap on tank, then screw it back on. Connect fuel line to motor. Pump fuel bulb till pressure. Turn key.
I do the same procedure all the time. If it is in the morning and it wont start I try to advance the timing and try the choke. In the afternoon It starts with no choke or advanced timing with about a second of starter. It starts instantly when its gonna start.
 

TenE3072

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Mar 15, 2011
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So I have tried cleaning the grounds and still wont start in the morning. Can someone please help, I am planning on taking it camping on Thursday but I am almost positive it wont run sitting in the lake if it wont start in the morning out of the water. Any suggestions are extremely grateful!!!
 

mrmotts

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Dec 27, 2016
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they can be a bear to start in cold temps, but it's odd you're not getting anything. it's hard to flood them and they need lots of gas to start. here's my cold day start procedure:
fully charged battery
trim engine back all the way so fuel runs down into carbs
prime the heck out of the bulb, should see some gas dripping from carbs
advance throttle halfway in neutral, choke while starting
if nothing after 2-3 tries, prime again and retry
then try full throttle in neutral - gotta be jonny on the spot to bring it back down after she kicks over though
could also try squirting some 50/50 premix into carb throats
 

TenE3072

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Mar 15, 2011
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Thank you so much for the suggestion! I got stung on my nose by a wasp today that had made a nest under the rail of the boat. I will try to almost flood it out in the morning if I get a chance.
 

TenE3072

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Mar 15, 2011
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I tried to keep pumping the fuel bulb and starting about 5 times until I saw gas coming out of the carbs. No start again this morning. I put my spark tester on my spark plug and as I have noticed before, I am getting no spark in the morning... As soon as I get spark it starts every time, so I dont think it is a fuel issue. Any other suggestions would be greatly appreciated!
 

TenE3072

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Mar 15, 2011
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UPDATE!!! I got my first 9 am start and on one of the coldest morning we have had in months! I looked at my coil that was off and I took off the metal cover and noticed there was a ground wire embedded in the rubber. I pealed the ground wire out of the rubber and pealed up the rubber and noticed the ground wire was embedded under the rubber also. I moved the ground wire out of the old ruts and screwed it back on the motor and it started right up like it is supposed to! I will keep testing in the morning and hope for a trip to the lake soon. Our camping trip is being postponed till next week, so my fingers are crossed that I will have the boat work at the lake!
 
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