field rescue

I am restoring a 1976 Thompson with an 86 V4 VRO 120HP Johnson. I have removed and cleaned fuel tank, all new hoses, removed the VRO and installed direct fuel pump, changed filter and spark plugs, gear oil, and installed new water pump. had carbs checked (above my pay grade). Motor runs great until exhaust is lowered into water at which time the engine stalls. I am not a mechanic, but am willing to give it a shot. In layman terms can anyone give me any advice. Last time the engine ran was 2013.

Sounds like the motors still needs work-----Always start with a compression test before spending a dollar on an abandoned motor like that.----Then check for spark on all leads.----Sounds like it is running on 3 cylinders.

racerone said:

Sounds like the motors still needs work-----Always start with a compression test before spending a dollar on an abandoned motor like that.----Then check for spark on all leads.----Sounds like it is running on 3 cylinders.

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thanks: compression checks good on all cylinders. Spark plugs leads must be good, starts instantly. stops is you cover exhaust. Had it checked out by mechanic with great reputation with no success.

lawms38 said:

compression checks good on all cylinders.

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What is good? Please post numbers for each cylinder.

lawms38 said:

Spark plugs leads must be good, starts instantly.

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An engine with poor spark can run and even 'sound good' when it's out of the water running on hose muffs. Out of the water there is no load on the engine so it doesn't take much to run. To verify spark you need to search this site for Joe Reeves' method for spark testing. here's the short version: all plugs out, fully topped off battery, using an air gap tester each lead should be able to jump a 7/16" gap. If not, then you have a spark issue.

lawms38 said:

stops if you cover exhaust. Had it checked out by mechanic with great reputation with no success.

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The "mechanic with great reputation" should have been able to do the basic troubleshooting that we are encouraging you to perform. When an engine won't run under load checking the compression and spark are always the first things to do. There's more troubleshooting to do once these are verified but please post the exact numbers of each then we can move forward.

As Kevin states in not so many words... do not reply with generalities such as good spark, great compression... replies which really has no meaning. You wouldn't want us advising you to take that rubber covered doo-dad from the top area of the carburetor and move it to the other side! You'd be flying back at us with... What the hell is this guy talking about, what doo-dad to which side of what?

On a flushette, out of the water, any engine will sound pretty good... and loud, especially a looper. However, usually it really isn't and the fact that the engine will not run properly (or not at all) when in the water proves it.

Standing in back of the engine, facing the spark plugs, the cylinders are numbered as follows on that 1986 Johnson 120hp Loop Charged engine:

2.....1
4.....3

* - All spark plugs must be removed during both tests:
* - Compression - What is the actual individual psi reading of the numbered cylinders?
* - Ignition/Spark - The spark must jump a 7/16" sir gap with a strong blue lightning like flame... a real SNAP! Does it?
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You state " had carbs checked (above my pay grade)" <--- What does this mean?

At the present time, I can only assume that you mean that the mechanic simply glanced at the carburetors, smelled the stale gasoline, then gave you a outrageous cost estimate to clean them which you couldn't afford.... so the carburetors are as they were in 2013 and NOT cleaned or/and rebuilt. <-- If this is the case, I can guarantee that the carburetors are fouled, gummed, clogged simply due to sitting for six (6) years.
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Air gap spark testers can be found at any auto parts store... or build the following:
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(Spark Tester - Home Made)
(J. Reeves)

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

..........X1..........X2

.................X..(grd)

..........X3..........X4

This can obviously be modified to a 6 or 8 cylinder setup tester.
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Get back to us with what you find and we'll do what we can to help you.

kevinj said:

What is good? Please post numbers for each cylinder.


An engine with poor spark can run and even 'sound good' when it's out of the water running on hose muffs. Out of the water there is no load on the engine so it doesn't take much to run. To verify spark you need to search this site for Joe Reeves' method for spark testing. here's the short version: all plugs out, fully topped off battery, using an air gap tester each lead should be able to jump a 7/16" gap. If not, then you have a spark issue.


The "mechanic with great reputation" should have been able to do the basic troubleshooting that we are encouraging you to perform. When an engine won't run under load checking the compression and spark are always the first things to do. There's more troubleshooting to do once these are verified but please post the exact numbers of each then we can move forward.

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Thanks for all the posts. I will do as suggested and appreciate it, but probably not this week. High 90s and will feel like over 100, and I"m over 80. Probably going to leave it alone until fall. Again, thanks for the posts.

lowest cylinder 105, highest 115.
spark tested with spark tester,not missing, is a redish color'
engine idles smoothly n yard. In water, hard to start, will not idle.

lawms38 said:

lowest cylinder 105, highest 115.
spark tested with spark tester,not missing, is a redish color'
engine idles smoothly n yard. In water, hard to start, will not idle.

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The engine must crank over at least 300 rpm in order for the stator (under the flywheel) to energize the powerpack.

The stator under the flywheel, look closely at it.... Is it dripping a sticky looking substance down on the powerhead area?

A slow cranking engine will generate weak, erratic, or no spark.

A reddish color........ jumping a 7/16" gap??.......... The 7/16" gap is important.

When idling "smoothly" in the yard... pull off one spark plug lead at a time to see if all cylinders react the same... drop the same amount of rpms? What happens?