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Mercury Black Max XR2 1986......motor runs like ONLY IN

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Mercury Black Max XR2 1986......motor...
Mercury Black Max XR2 1986......motor runs like crap ONLY IN THEWATER
Submitted: 2 months ago.Category: Boat
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Customer reply replied 2 months ago
I have lots of detailed technical information to share as well regarding what’s been tried and other observations
Answered in 3 minutes by:
5/25/2018
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago
Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 18,203
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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Hi Michael, good morning, my name is***** read what you wrote. Is there any kind of story or history to this engine, have you ever personally seen it run correctly. What have you down on your own so far?

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Customer reply replied 2 months ago
Glad you responded.... i’ve actually gone through a transcript you had regarding this motor with another customer as guidance.....ok are you ready?
Customer reply replied 2 months ago
Engine is well maintained and until recently ( just before I purchased ) it ran like a monster.....it was purchased from a longtime friend so I’m not worried about deception or abuse
Customer reply replied 2 months ago
Compression is very good.....120-125 on all cylinders.
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

okay got it. Did you buy just the engine and did you stick it on your own boat, or did you buy the boat and motor as a combination?

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Customer reply replied 2 months ago
Fuel is clean and oil is mixing proper, tank cleaned, zero water, carbs spotless, fuel pressure 1.5-2lbs before and after the filter. switchpacks replaced but tested ok Incl Ohms test on bias circuit
Customer reply replied 2 months ago
Boat and motor bought together
Customer reply replied 2 months ago
Stator tests proper, trigger tests proper, idle box in the trash where it belongs, timing set to 22 WOT
Customer reply replied 2 months ago
Runs like an animal in the driveway with muffs......but as soon as you put it in the water......like a potato in the tailpipe
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

Got it. Did you test for spark output on all 6 cylinders by taking the timing light and hooking it up to each plug wire 1 at a time, and seeing if that timing light flashes or not?

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Customer reply replied 2 months ago
Spark good on all cylinders. New coil packs too
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

Did you check the spark on land, or with the boat in the water and under a load?

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Customer reply replied 2 months ago
I’m 99.9% confident I’ve covered all the bases on ignition and fuel.....I’m looking at backloading from the exhaust
Customer reply replied 2 months ago
Spark tested on land only
Customer reply replied 2 months ago
I have a video clip of the motor idling while in the water......there is zero exhaust coming out the lower leg/prop hub......only through the relief holes in the cowling
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

The spark test really should be done one on the water. The engine can show good spark on land, but that spark can break down in the water, especially if the flywheel mags are weak or broken. So you will need to do the spark test with the boat in the water. Have you tried running it with the engine cover off while in the water? Or have you always run it with the cover on?

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Customer reply replied 2 months ago
Cover on. Flywheel was off to change the Stator so I know there are no loose/broken magnets as well
Customer reply replied 2 months ago
Engine only run with cowling on in water
Customer reply replied 2 months ago
Nothing I’ve mentioned about the exhaust is putting up any flags I take it?
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

Nope, nothing with the exhaust is raising any red flags. When do you think you can get back out to the boat to check a few things?

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Customer reply replied 2 months ago
Of note regarding the flywheel.....it runs a little out of true.....it’s fine across the top so the bearing isn’t shot......but on the lower side with the teeth.....it has a slight warp to it....obviously not good but a super longshot to be causing this problem
Customer reply replied 2 months ago
Glad to hear about the exhaust.....I was very disinterested in pulling the powerhead off....I can put the boat in the water any time
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

Nope, nothing with the exhaust is raising any red flags. When do you think you can get back out to the boat to check a few things?

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Customer reply replied 2 months ago
It’s here in my driveway, I can work on it anytime.....I’m self employed and I’m on a short term prescription from Dr. Summeroff
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

Do a couple of things. First, pop the engine cover off, run the engine, then with it running, hold your palms as flat as you can against the throat of each carb. You are looking for 2 different things here. You are looking for 1. You want to see if you feel suction against your palm, or if you feel any pressure or fuel spitting back out at you and 2. You want to feel if the suction feels equal on all carbs, or if certain carbs have noticeably more or less suction than others. The 2nd thing you want to do is throw the boat in the water, and see if it runs better with the engine cover off. Let me know how you make out.

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Customer reply replied 2 months ago
10-4......vacuum check?
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

Similar to a vacuum check.

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Customer reply replied 2 months ago
I may not be able to do the water test until Sunday ( weather here ) I assume this conversation can be picked back up at any time?
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

yes of course, there are no time limits here.

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Customer reply replied 2 months ago
You want the airbox cover off while on the water too I assume?
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

No, just the engine cover.

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Customer reply replied 2 months ago
DVA adapter for my meter literally just arrived......so I have a baseline....what would be the correct way to check spark without accidentally numbing my arm?
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

With the timing light. Hook the timing light up to each plug wire one at a time, bring the engine up to full throttle, as fast as it will go with the boat in the water and under a load, and see if the timing light flashes evenly and consistently with engine rpm or not.

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Customer reply replied 2 months ago
I meant intensity......I can already verify I have consistent spark both on land and in water ( I DID do the timing with the leg in the water )
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

That's all you need to do for the actual test.

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