Engine is afraid of the water

[Enginefixer]

I am a newbie to all this. I bought an older boat and motor combo, and the engine is a 1979 100 hp (100ML79S)Johnson. I sat for a couple of years but was drained and flushed prior to putting away. Got it home, fresh gas and oil, changed the oil in the lower unit and test fired. Seemed to run great. Changed the gas line, as the old one was hard as a rock, and added a filter. Once again the engine ran great on the flusher, no overheating, good flow out the pee tube etc. Once warmed up will fire at a touch of the key. Brought it to the river and dropped it in the water. Ran like crap, wouldn't idle even after running in warm up for a bit. Thought maybe I was sucking air. Checked all the fittings, changed the hose to tank and hose to engine connectors, tightened all the clamps etc. Ran again at the house and sounded like I had a winner. Brought it to the river again, and as soon as it got wet, same thing all over agian. Started fair, idle went down to nothing and died, pian in the butt to restart. Drug it home again, and here I sit. Any and all ideas would be much appreciated.

 

[nwcove]

i would start with a compression test, then a spark test. they will run quite well on muffs without actually running on all cyls.

 

[Enginefixer]

Thanks that is what I was thinking, just wanted a second opinion

 

[racerone]

The compression test is the first thing to do.--------I am amazed at how well these engines will run with broken pistion rings.---I buy these motors all the time and see this damage.----Amazed that folks will keep running them untill they basically lay down and die !!!

 

[Enginefixer]

Compression is 115 all cylinders, so that is a good sign. right lower cylinder is not getting spark. Have to look at troubleshooting the ignition system. Coil readings are the same for both cylinders, as is the plug wire reisistance for both right hand cylinders. Have to figure out how to troubleshoot the powerpack and see if that is the problem.

 

[Enginefixer]

Ok, so I swapped the powerpacks from right side to left side and the problem followed the powerpack, so next up is a new powerpack and then back into the water for another op test. Didn't think that just putting in the water would make that much difference. Hope this works.

Thanks for all the input. Hope that I can help others out some time!

 

[KRH1326]

I think that I am learning a lesson about setting the timing on a hose will result in bad/ low idle and stalling at the dock. Timing should be set, in the water because of the back pressure...Maybe same issue is at work here...

 

[emdsapmgr]

You can't set the idle when the engine is on the trailer. The idle will be completely different when the exhaust comes out 20" underwater. You have to set the idle when the boat is floating normally in the lake and it's in forward gear. Set the idle to 650-700 rpm's.

 

[1946Zephyr]

I was going to point to faulty ignition system. I have seen many cases where they run good in the yard, but crappy on the lake. The humidity on the lake is enough to make them arc out on the nearest piece of metal.

 

[Enginefixer]

Changed the powerpack, also got a new rectifier while I was in there messing around. Engine started and stayed running in the water, which it would not due previously. Tach still does not work, but based on the age of it, go figure. Took it out in the river and at first very little throttle response. As i was about to concede defeat, the engine took off like a rocket. Guess it just needed to cobwebs knocked out of it, and ran like a scalded dog for about half an hour. Thanks again for all the replies. Now to fix the gauges.