1979 Mercury 900 Running Rough AFTER I Ran Aground

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chuck25624

Cadet

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Jul 7, 2008

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13

• Aug 31, 2011

• #1

Hello! I have a 16' 1979 Glastron Sportster XL with a 1979 Mercury 900. The motor ran great until I hit some rocks, in the shallows. I tore up the prop pretty good. I had to jump overboard and pull the boat out into deeper water and away from the rocks. I got back in and tried to start the motor. It didn't want to start. It was like she wasn't getting enough fuel. I chocked it, gave it throttle and she started...barely. Now, I have to get it into gear. Long story short, it took a bit of trickery to get her going. I got in, got home and started her up. She shakes and runs real rough. Could I have knocked her out of time when I hit the rocks? Any info is appreciated. Thanks!

 

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Mi duckdown

Commander

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Apr 14, 2007

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2,575

• Aug 31, 2011

• #2

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

Could Be. Got pics of the Prop.

 

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Chris1956

Supreme Mariner

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Mar 25, 2004

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27,149

• Sep 1, 2011

• #3

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

Probably you did not change the timing. You may have bent the propshaft, and likely you ruined the prop.

Inspect the powerhead for any damage.

 

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chuck25624

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• Sep 1, 2011

• #4

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

OOOOOHHHHHH yes. The prop is destroyed. I put a new one on, and it appears to be true. What kind of damage should I be looking for on the powerhead? Thanks!

 

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Chris1956

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27,149

• Sep 1, 2011

• #5

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

I would look for broken items, pinched or rubbing wires, frayed fuel lines, leaking carbs. That kind of physical damage.

 

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chuck25624

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13

• Sep 1, 2011

• #6

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

Everything looks good. Nothing out of the ordinary.

 

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daydreamer1252

Petty Officer 1st Class

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Aug 7, 2007

Messages

212

• Sep 2, 2011

• #7

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

Not been in one myself....but does the the flywheel use a key and key way for location??? Wouldn't be the first time one broke and a flywheel slipped....

 

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chuck25624

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13

• Sep 2, 2011

• #8

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

I will check that out! It didn't occur to me.

 

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Chris1956

Supreme Mariner

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27,149

• Sep 3, 2011

• #9

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

Those Mercs have a "w" machined into the flywheel and crank. No woodruff key to shear.

 

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chuck25624

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• Sep 3, 2011

• #10

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

Correct. Just for kicks, I'm going to check the compression. I'd like to get out at least one time this weekend.

 

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CharlieB

Vice Admiral

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Apr 10, 2007

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5,617

• Sep 3, 2011

• #11

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

A serious jolt may have stirred up some crud from the bottom of the fuel tank and now is in the carbs.

Remove the float bowl drains, one at a time, pump the primer bulb and see what gets flushed out.

It may be a good idea to install a water separating fuel filter to prevent future problems.

 

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chuck25624

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13

• Sep 3, 2011

• #12

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

Compression is 115 in all cylinders except #6. That one is at 100. Any thoughts?

 

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Garrett1992

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Mar 13, 2011

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28

• Sep 3, 2011

• #13

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

I would definately start by checking the timing...then maybe check to see all cylinders are firing

 

Gomer50

Chief Petty Officer

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Sep 5, 2009

Messages

507

• Sep 3, 2011

• #14

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

First I would drop the lower unit and and inspect the drive shaft.Then I would start the motor with the lower unit off and water hose attached to the plug/hole right below the number 2 cylinder.There should be a brass bolt/plug.This way the motor will have water cooling while running.
This will give an Idea if the motor still functions without a wobble should there be any problems with the lower unit.As for your compression numbers 100 Psi is a little low actually 115 psi is a little low as well.But given 10% difference between all cylinders is good news.I dont think the power head suffered any damge,If anything the lower unit suffered and maybe the the splines on the bottom of the crankshaft or driveshaft.

 

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chuck25624

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• Sep 6, 2011

• #15

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

What should the compression be? Actually, I took the compression when the engine was cold.

 

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Chris1956

Supreme Mariner

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Mar 25, 2004

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27,149

• Sep 6, 2011

• #16

Re: 1979 Mercury 900 Running Rough AFTER I Ran Aground

Your compression is fine, on a motor that old. I vote for there being crud in the carbs.

After you get it to run on the muffs, prop off. Inspect the spin of the propshaft in forward. See if you can detect any bending. Next test is water test with known good prop.