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how do i test to see if all the cylinders are firing???
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how do i test to see if all the cylinders are firing???
hello all, i am working on my dads 78 mercury 90 hp outboard. i replaced the fuel line and water seperater and inline filter, i start it up and she still sputters once in a while. last year when i was pulling the boat out of the slip, it started right up and i started speeding up and she bogged down!! what is the easiest way to test to see if all the cylinders are firing??? without getting shocked.
RE: how do i test to see if all the cylinders are firing???
Quote:
seaswirl - 5/21/2005 1:59 PM
hello all, i am working on my dads 78 mercury 90 hp outboard. i replaced the fuel line and water seperater and inline filter, i start it up and she still sputters once in a while. last year when i was pulling the boat out of the slip, it started right up and i started speeding up and she bogged down!! what is the easiest way to test to see if all the cylinders are firing??? without getting shocked.
Go down to the auto parts store and buy a little spark tester that goes in between the wire and the plug
Re: how do i test to see if all the cylinders are firing???
An inductive pickup timing light can be used for this as well. The adjustable spark tester mentioned by Vectorfish above is great because it lets you see if the correct strong spark jump width with can be obtained- important under compression & with fuel/air mix swirl.
Re: how do i test to see if all the cylinders are firing???
With the motor running grab one sparkplug wire at a time. When you grab it if it makes you bite your tongue chances are it's firing. The first few times you check it you will not feel good but after a few hundred times you'll get to the point where you will enjoy it.
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Re: how do i test to see if all the cylinders are firing???
This test will work with a single cylinder engine, but it is pointless to do so. You will notice a significant RPM drop when performing a power balance test on a "one lunger".
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Re: how do i test to see if all the cylinders are firing???
Here's an easy way to do a cylinder balance test while the engine is running and not get blasted. Go to the parts store and buy a 12 volt test light and a foot of 3/16 vacuum line. Cut the vacuum line into 2 inch lengths. Remove each plug wire and reinstall it with the vacuum line between the plug and the wire. Secure the clip end of the test light to some bare metal on the engine to ground it. It must be grounded. Now just start the engine and once it's warmed up, simply touch the probe of the test light to one vacuum line at a time and make note of RPM drop. It's best done with a tach to see if each cylinder drops the same amount of RPMs but even listening to the RPM drop will tell you if the cylinder is dead. If the cylinder is weak as opposed to dead, I would strongly suggest a tach as it will be a much more accurate test. Now before I get flamed by someone who wants to point out to me that vacuum line is rubber and therefore doesn't conduct electricity, let me point out that MOST vacuum line has a high carbon content (Just like plug wires) and will conduct some current. If you want to be sure, check the resistance of the vacuum line using a high scale on an Ohm meter. Any reading at all other than OL or open circuit will work just fine. This test works great and is so much better than pulling wires off while the engine is running which can hurt like hell but can also take out expensive ignition components.
Re: how do i test to see if all the cylinders are firing???
thanks everyone, i have someone that is an retired mechanic, i am mechanically inclined but im no mechanic. i will let you know how i make out. thanks again
Re: how do i test to see if all the cylinders are firing???
I don't have an outboard, but I do have a snowmobile with a liquid cooled 500cc twin. When it feels like its only running one cylinder, a simple test of putting my hand near the end of the plug wire will tell me. It one cylinder isn't firing, it stays a lot cooler than the other one. I assume teh same would work for an outboard.
RE: how do i test to see if all the cylinders are firing???
I havent tried it on an outboard but it works on an inboard and an IO most of the time.
Take a spray bottle full of water adjusted to spray a narrow stream.
With the motor running spray the exhaust manifold close to the cylinder head. The water will instantly vaporize on cylinders running well and will not on the non-firing cylinder.
Its worth a try. No tools to buy.
Re: how do i test to see if all the cylinders are firing???
My guess is carbueration trouble
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how do i test to see if all the cylinders are firing???
