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I am wanting to perform a compression test on my motor, altough it still runs good, idle is quite rough and can stall at idle when in gear.
I have seen all sorts of DIY videos on the web on how to do this, but it just seems too easy, I did not see one grounding the plug wire to motor block.
My understnding is that if the spark plug wire is not grounded it can cause serious problems to the ingition system.
Can someone indicate what is best procedure for grounding or is it better to get a remote starter switch and connect to the starter solenoid while leaving the ignition key at off to do the test.
I want to get the carbs done, but most service shops do not want to touch as it is too old and parts are getting very scarce.
Last week we went out twice and ran a total of 37 miles, of that 18 was pulling a tube, not a single failure.
All new gas lines
New fuel tank
Idle mixture adjusted as per manual
Carb cleaner used on carbs
Gear case does not take on water
If not for idle issue the motor still looks like new under the cowling
But before I put money into the carbs I want to at least sure I have good compression in the cyslinders, do not want to spend money for nothing
Although I am not an outboard mechanic and use Mercury dealers for engine service problems, I do have some experience with your generation engine, albeit the six cyllinder version. I own three of them (see Montauk and 21 Outrage photos on personal website link). The 75/80/85's are the 4 cylinder version of the six cylinder "towers". If everything is checked out as you say, and idle stop and low speed carb setting are correct (600RPM in gear idle speed), and the engine still idles rough and dies out when shifting into gear, first of all be sure the carbs are clean and completely overhauled, and installed and sychronized properly. I would also make sure all of the electrical/electronic components are good.
If those are good, you are wise to check compression. I can't tell you how to do it, however!
Lastly, if the idle situation STILL does not correct itself, with everything else checking out and compression within normal wear limits, and with a skilled mechanic doing the work, you probably have a reed problem, which requires an engine teardown and rebuild. A weak idle, and inability to fix it with all of the above mentioned work, usually means bad or worn out reeds. All of the parts needed to re-build one of these engines are readily available. Hopefully that won't be your problem. I would get the engine to a service shop experienced with this generation of Mercs even if travel is required.
There are two good on-line website sources for technical help on old Mercs. You might inquire there also.
Last week we went out twice and ran a total of 37 miles, of that 18 was pulling a tube, not a single failure.
Might try running some carb cleaner through them before you get too carried away with the rest of your list :) Also, insure your gas tank and gas is fresh, you might have had some separation of the gas/alcohol or even water condensation if the boat set up for a few months right before you had the problem.
Gas should be good, it is a new tank (2 weeks old) and has had only premium fuel in it, no ethanol. Fuel line and bulb were replaced last year with top quality parts
Took out the plugs this afternoon and they were in worse shape than I expected, there was carbon deposit on 3 of them except one had less carbon deposit than the others.
Cleaned the plugs, need to go buy a new set of plugs and spares
Put it on the muffs and ran some Sea Foam though the carbs, followed instructions and noticeable smoother idle on the muffs.
Will water test on the weekend, would still like to do compression test. Neighbor has a compression gauge, just need to make sure I follow proper procedures not to create more troubles.
The lower cylinder is the one that had the less carbonized plug and is the probably the one that will be the hardest to test with the lower cowling leaving little room to work.
By the way this is a great site, in my second summer with my Newport and the knowledge found here has been of tremendous value.
So far where I boat I am the only Whaler on the water and I get stopped regularly and people ask what is it, they are amazed when I tell them it is 36 years old
I will need to post pictures of all the work done so far.
Since you mention carbon on the plugs, the other thing you should definitely do is run a shock treatment of Mercury "QuickClean" through the engine. Use a whole bottle with 12 gallons of gas. This will completely decarbon the cylinders, pistons, rings and engine internal passages, and clean up the carbs also.
Then use it at it's prescribed dosage once a month.
Quickclean is the best product you can buy for keeping a 2 stroke, traditional or DFI, decarboned internally. Yamaha makes a similar product called "Ringfree", equally as good, and for the same purpose.
Thanks Finnegan for the suggestion, will give a try early Saturday morning, I will turn on the GPS and find out out how far i go on 12 gallons without stopping.
I have tried your shock treatment for my old Merc and the results are quite positive, I went out yesterday morning with the intention of running my 12 gallon tank empty but after 23 miles I decided to stop and fish instead.
So far the engine is running smoother at idle, does not stall when putting in gear.
I also noticed that at the prop exhaust a good coat of black soot, so something is being blown out of the engine.
Well the shock treatment worked for awhile, but now idle is good but motor is harder to start and after some 10 to 15 minutes of cruising the motor dies and does not restart, also fuel is accumulating in pan in front of carbs
So it will be off to the repair shop shortly, I did do a compression test and all 4 cylinders were at 125 pounds
