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Abiorca, Marine Mechanic
Category: Boat
Satisfied Customers: 1824
Experience:  Over a 15 years of working on all the brands of outboards.
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1980 90hp MERCURY. Has been hard starting. Have to use ...

Customer Question

1980 90hp MERCURY Inline 6. This model does not have a distributor. It has been hard starting for a while and have had to use starting fluid to get it start when cold. I can get it started and keep it going but only over 1000 rpm. It sounds good at that speed. But below that, it dies. I was told it might be reeds. But I never saw or heard any spurting out of the carbs. Someone else told me it might be an electrical thing or timing. Your thoughts please.
Is there a way to determine if the reeds are damaged without tearing down the engine. These reeds are on the crank shaft.
Could the idle stabilizer cause this problem?
Submitted: 9 years ago.
Category: Boat
Expert:  Abiorca replied 9 years ago.
Hi Hals,
Ok where to start, all the thiings you have pointed out can cause a problem to the idle, what you need to do is take a methodical approach to this problem, remove the plugs and do a spark check do you have a spark on all plugs?
While doing the spark check do a compression check, all cylinders should be over 100psi and within 15psi of each other.
If the spark check and compression come out ok then assume its a fuel problem, strip out the carbs and clean them out, I use a product by Quicksilver called power tune DONT FOLLOW INSTRUCTIONS ON THE TIN use it to blow through everything on the carbs it will deglaze everything and is the best carb cleaning product out there! While the carbs are off you can shine a torch down the inlet manifold and just about see most of the petals on the reeds, I think if the one of the reeds had gone this will be evident on the compression test as they usually take out a piston on the way through the engine.
Once carbs are on and you have synchronised the carbs back up if the problem is still there then you will need to move onto the electrics.
Many Thanks Orcamarine
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Customer: replied 9 years ago.
I will check the spark and compression but both are probably ok because it runs ok above 1000 RPM. Carbs were cleaned already. Is there a way to check the reeds without breaking down the engine. Shouldn't there be a vacuum created at each carb at least one that can be felt with your hand. What does the idle stabilizer do. If I remove plugs and crank engine, can the low speed timing be checked. What should the timing be at idle and WOT.
Expert:  Abiorca replied 9 years ago.
Hi Hals, as its a 6 cylinder the compressions can still be low on 1 or all 6 if the engine is worn out, I know this sounds contradictory to what you know but the engine may only be producing 60 hp with lowcompression not the full 90,
The idle stabalizer plugs onto the cdi unit and basically stabalizes (smoothes out) the idle. this needs to be disconnected before you can do the timing, I cannot remember from the top of my head what the timing should be but both idle and WOT can be done statically, if you get to the point that you are convinced it is the timing as its quite an involved job I would reccomend you get the manual.
Many Thanks Orcamarine
Customer: replied 9 years ago.
I have swapped out this 90hp with an old 85 I had. Next week I should be able to get the 90 home and will do the things you recommended. Is it possible to continue this issue if I cannot resolve the problem. How would I do that, so I get you instead of someone else.
Expert:  Abiorca replied 9 years ago.
Hi hals I am not sure but I guess if you go into "my questions" and just continue this one, or start a new question with my name in the title.
Many Thanks Orcamarine