1985 MerCruiser 3.0L Tune Up?

bill 22

Petty Officer 2nd Class
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1985 Mercruiser 3.0L M# MCM 140, SN: 6922598, with Mercarb, with electronic ignition kit (NO points or condenser).

I need to tune up my engine. I am sure that there are many good post and write ups about tuning up an old Mercruiser.

Do the pros out there have one or two favorite post that list detailed tune up steps? I don?t see any reason to ask someone to rewrite what is already done.

I?m having trouble starting my boat when the engine is warm. The choke is opening up all the way when the engine is warm.


Thank you,
 

bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

here are some more details:

This is a normal day: put the boat in the water, pump throttle 1-2 times, turn key & boat starts up, boat runs 30 sec. & stops, adjust idle screw up 1/2 turn, start boat & runs GREAT, when engine warms up idle is high, adjust idle screw down 1/2, idle is fine now, shut off boat, try to start boat again & boat will not start, pump throttle and try several times boat still will not start, adjust idle up & pump throttle, boat starts.

I know something needs to be adjusted/cleaned or is not working because I should be able to set the idle and leave it.

Bill
 

bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

I did some preventive maintenance yesterday;

installed new fuel filter in fuel pump, installed a new distributor cap (old one was very old), cleaned the rotor button, cleaned and check gap of spark plugs, cleaned the flame arrestor.

The flame arrestor was dirty. I cleaned it three weeks ago by pouring gas on it, shaking it out and blowing it off with compressed air. Yesterday I used carb cleaner and got a bunch of black junk out of it.

Next I plan to run it and spray some carb cleaner down in the carb. Then put it in the water for a test run.

Any other ideas?
 

Don S

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Re: 1985 MerCruiser 3.0L Tune Up?

Do you use the throttle only position on your throttle/shift control?
 

bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

Don,

I wish that my shifter had a throttle only button. It looks like it might of had one and was broken off. It has never had one since I bought this boat.

In a differnt thread that you are also helping me you said, With those compression numbers you need an overhaul.

I don’t understand why my compression is so low. Compression test numbers, something like 1= 115psi, 2= 95psi, 3= 75psi & 4= 55psi (I have the readings at home). I just had the engine completely overhauled by a pro four years ago and have low hours since then.

Thank You VERY much for your help,
Bill
 

Don S

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Re: 1985 MerCruiser 3.0L Tune Up?

Post a picture of your control.
If it is broken, then fix it, or replace the control.

I don’t understand why my compression is so low.

Hard to say, maybe you did the compression test wrong, did you look at the service bulletin I posted on your other thread about the compression? Please don't post the same question in multiple threads, makes it really confusing.
 

bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

did you look at the service bulletin I posted on your other thread about the compression?

I read the bulletin and printed a copy. I will repeat the compression test following the bulletin.

I’ll let you know what I find.


Sorry for posting on multiple threads.
 

bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

I have a feeling that it is the head gasket. The head gasket blew out last year at the #4 cylinder. I cleaned the block & head and checked them to be flat. I use a carpenter square and did the best I could. They looked ok to me. Then I installed a new gasket.

I was hoping that the old gasket failed because it was defective.
 

bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

shifter 1.jpgshifter 3.jpg This is my throttle. You can see in the first pic there could have been a button there.
 

Don S

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Re: 1985 MerCruiser 3.0L Tune Up?

Put in neutral, pull the handle out away from the control and move the lever forward. Throttle only. Pull it all the way back to neutral and the handle will pull back in and you will be able to shift gears again.
 

bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

Put in neutral, pull the handle out away from the control and move the lever forward. Throttle only.

That is great news. I feel a little stupid that I did not know that. Our old boat had a button for throttle only. The guy that sold me the boat did not tell me that important little bit of info.
 

bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

thank for the help!
 

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bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

Put in neutral, pull the handle out away from the control and move the lever forward. Throttle only.

Don,

I gave this a try and no go. I pulled on the shifter and it never moved out or went in to throttle only. I pulled at the base and at the top of the sifter handle. I gave it a good tug but it did not move.
 

Don S

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Re: 1985 MerCruiser 3.0L Tune Up?

Was you in neutral when you tried to pull it out?
 

bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

Yes, I was in neutral with the engine running and boat in the water.
 

bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

Don, Thank you for the help with the control.

For my compression problems should I start over with a new thread or continue that topic with this one? I have the procedure you gave me and I want to do more testing to get to the root of my compression problem.
 

Don S

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Re: 1985 MerCruiser 3.0L Tune Up?

For my compression problems should I start over with a new thread or continue that topic with this one? I have the procedure you gave me and I want to do more testing to get to the root of my compression problem.

I gave you a link to how to do the compression test, did you read it? Do the test again using the proper procedures and see if they come up. With the compression you have, you're lucky it will run at all.
If you had that engine rebuilt 4 years ago, then you really need to find out what is killing engines.

You have burned up head gaskets, lean running? Timing incorrect? if that is happening to the gasket, what does the valves look like.

It would have been real handy to have done a leak down test prior to taking the head off. Just so you know what and where to look at.
With the head off, you are down to visual inspection, and if you don't understand what you are seeing, you have no way of knowing if what you see is good or bad.
 

bill 22

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Re: 1985 MerCruiser 3.0L Tune Up?

I have not removed the head or head gasket. The pic above if from when the head gasket went out last year. In August 2011, I cleaned everything and installed a new head gasket. At the time I looked at the valves and they looked ok. Also I looked at the cylinder wall and it looked good as well. I put a straight edge on the head and block. Both appeared to be flat.

I did read the leak down test procedure. Also, I borrowed a leak down gauge from a friend. I plan to follow the procedure and do the leak down test soon. I'll let you know what I find.

Thanks,
 
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