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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I have a 1985 mercury 115 inline six outboard. It runs fine

Customer Question

I have a 1985 mercury 115 inline six outboard. It runs fine when just started and will run at any speed you set the throttle at. After about 10 minutes after engine warms up and you back it down to idle; it will not accelerate again and falls on its face. if you let the engine cool down about a half hour it will work fine again until it warms up. I ran it for about 30 minutes at 2500 rpms with no problem when first starting, but when I went to idle speed it would fall on its face again. Any suggestions?
Submitted: 1 year ago.
Category: Boat
Expert:  Jeff G. replied 1 year ago.

Do a couple things. First on top of the float caps is a brass air jet. Remove the jets. Don't put anything in their place. This richens the mixture at midrange which cools the engine. See if this doesn't cure the problem.

If you have a IR non contact thermometer, check the temperature at the top of the block. Does your engine have the tell tale fitting on top of the block?

When it goes to accelerate and falls flat, look into the carbs, are they dry or wet?

Try a quick application of the primer then accelerate. But remove and try the engine without the jets first.

Let me know how it does.