1985 75hp mercury starting trouble

marzoid

Seaman Apprentice
Joined
Oct 12, 2011
Messages
40
1985 75hp 4 cyclinder
Serial # 6616110 If someone wants to double check that I got that right.


Ive been going at this for a very long time. My motor will not start properly. Any help would be greatly appreciated.

Compression readings from top cylinder to bottom...140, 140, 130, 130
Is this anything to worry about?

I should also mention that a few months ago I was not getting spark on 3,4. After replacing spark plugs, spark plug wires, and the powerpack(coils.) I found out it was my harness wires that connect from the switchbox to the coils. Once I replaced those I was able to get spark. Thanks again for helping me out on that.

At this point I was able to get the motor started and running only when I would pushed the throttle button in and moved the lever all the way forward. It would then be able to start. When I would move the lever back down it down soon die. I was not able to start the boat in idle without the throttle lever pushed forward - at all.
Note: This was my problem before I had to replace the harness wires as well.

I have tried the following.

-Adjusting the idle screws on both carbs. I only stayed between 1 and 1 1/4 turn. It sounded somewhat close once but nowhere near actually starting. I feel like I tried every combination. Wish I marked where it started at full throttle now Im having trouble finding that.

- I took apart the carbs and cleaned them with carb cleaner and air compressor. Things I should mention the first carb was missing the inlet needle and the second one had the needle put in backwards. I replaced the first one and put the second one in the correct position. This is according to the specs shown below....could this possibly be wrong...Part Number 3 is the one im talking about. I also replaced the gaskets. I did not touch the float or the pin needle(part 7) Seemed in good condition from what I could tell.

http://www.**********/parts/search/...6432901 AND UP/CARBURETOR ASSEMBLY/parts.html


- Ive recently taken apart the bottom to check the shape the impeller was in. It seemed like it was in good shape. I replaced it anyways. Im having trouble putting the bottom back onto the motor. Seems like its close but cant quite get it. I have both drive shafts lined up and the waterpump valve connected. Screws are lined up. Is there something Im missing? sorry to get off topic.

I noticed a pinhole sized hole on my exhaust tube. PART 10....on the picture it is located on very near to the bottom...the back left side that is not shown in the picture. Is this something I should fix somehow?


When I press the bulb the bulb does stay hard. I do have a very very small leak by the fuel filter that I believe can be fixed with a new gasket. It only leaks when I keep pushing on the bulb after it is hardened up. It will unharden a little after trying to start the motor.

Where should I go from here?

Ive been told my carbs could be clogged up in the chambers and need professional cleaning (ultrasonic to break down whatevers jamming them up)

Neutral safety switch could this be causing this? not exactly sure how to test this. Have not looked into it yet.

Is it my timing? Have not tried setting this as I do not properly understand it when I have looked it up. Dont want to make things worse.

Is my compression bad?


Any help would be appreciated. If possible I would like to fix this myself. Enjoying the learning process although Im putting a little too much time into this. Thanks for any help/suggestions.
 

aussieflash

Lieutenant Junior Grade
Joined
Feb 5, 2011
Messages
1,004
Re: 1985 75hp mercury starting trouble

Serial # checks out fine.Compression OK..(maybe seafoam treatment down the track may even them up).Strip down carbs completely and spray every crevice and let sit for 1/2 hour,rinse then repeat with solvent and blow dry.Replace all needle n seats to make sure.All carb floats should be checked for cracks or saturation,most important they must be reset to exact height spec.(Mercury Service Manual)<<<< A MUST.
Starting problem could also be faulty/misused enrichener/choke.
 

xanderman

Cadet
Joined
May 12, 2012
Messages
7
Re: 1985 75hp mercury starting trouble

Serial # checks out fine.Compression OK..(maybe seafoam treatment down the track may even them up).Strip down carbs completely and spray every crevice and let sit for 1/2 hour,rinse then repeat with solvent and blow dry.Replace all needle n seats to make sure.All carb floats should be checked for cracks or saturation,most important they must be reset to exact height spec.(Mercury Service Manual)<<<< A MUST.
Starting problem could also be faulty/misused enrichener/choke.

To get the bottom end the last little way up you might have to align the splins of the drive shaft with the power head. Slowly turn the flywheel by hand a tiny bit then try again to push the bottom end up.

Also make sure the throttle is in the forward gear position and the smaller spline gear on the front is rotated all the way counter-clockwise, so both the control lever and the gear box are in forward.

Do not force it, it will slide in relatively easily if everything is aligned correctly.
 
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