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1988 mercury 100

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Frige

New member
I just picked up a 1969 Thunderbird with a 1988 100. Last time it was started was at least 4 years ago. Where do I start? Also the last owner says the trim doesnt work. Should be a fun project.
 
Also I read somewhere that the only difference between a 100 and a 125 is the carburetor. So can I bump up the hp just by changing the carb?
 
Well got her to fire up. Only runs on 3 cylinders. No fire to #1 Switched wires with #2 and there is fire. I believe it is the little black box. Found one on Ebay for 60 bucks. Also looks like the trim pump motor is done. It has power but doesnt run. Ugh looks like I have to pull the motor.
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You need to purchase a factory service manual for this engine, specifically for this engine group. You need to educate yourself before you start pulling the engine and replacing "black boxes". Don't make assumptions about the repairs that you don't understand. Everyone here will help you if you want the help.
 
Well thats why Im here to ask for help. So how should I troubleshoot this? I am replacing the impeller and the seals in the lower unit. Im kind of a jack of all trades around engines. But I have never worked on a mercury.
 
It's a unique design engine called a 2+2 engine. It only idles on the top 2 cylinders at idle, but it is has spark on all 4 with no fuel delivery to the bottom 2 cylinders with just enough to lubrication to lubricate the rotating components without enough fuel to fire. There are no idle mixture screws on the bottom 2 carbs.
 
Interesting. Guess I better not get the carbs mixed up. Lol. When I was troubleshooting the lack of spark on #1 I switched the low voltage wiring on the coils. #1 then had spark and #2 did not.That is how I determined it must be the the cdi module. While I havent pulled the flywheel I assume it must have a crank trigger. If so it only tells the cdi where the tdc is and so the cdi triggers the spark to the individual coils. Is this correct?
 
Just to let y'all know, the cdi fixed it. We also had to disassemble the trim motor as it wasnt working. Found it badly corroded and stuck. Pulled it apart, cleaned and lubricated it and now it works fine.
 
If it was a later model you can put the 125 carbs on and vola...125Hp. You have the small bore 88 100hp and its doing all it can do...
 
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