140hp Johnson No Top End

[richcraft]

I have rebuilt the powerhead on my buddies 1979 140 Johnson. It is on a 16' Peterbourough. Before th rebuild it would top out at 57mph. After the rebuild we could only get 43mph. I have cleaned the carbs, changed the fuel line, had the fuel pump apart and cleaned the screen. Nothing seems to make a difference. I did not check the timing but we didn't adjust anything so I think it should be fine.
The motor was bored .030 and added new slugs, bearings, gaskets etc.

Any ideas would be much appreciated.:thumbsup:

[flabum1017]

How's the compression? And why did you rebuild it?


Timing is very important,,,,,,, you really need to chek the timing.

[richcraft]

Reason for the rebuild, it blew up. Buddy lent his boat to another buddy for the weekend and apparently he did not mix the gas. Burnt 1 piston.

I will do a compression test and check the timing.

Thanks

[Forkin' Crazy]

Are you sure it's running on all 4? Check the spark. I've seen a bad plug out of the box and fought that too.

[EMDSAPMGR]

What do the plugs look like. Wet, dry, all the same? Check each plug wire for spark with an indcutive timing light.

[jody504]

Check the plugs on the power pack you may have one pin that didn't line up seen that more than once on them older v-4.Make sure the trigger can move the hole distence from stop to stop.

[omcnut]

I had the same problem with my 79 140 Rude, and I immediately started jumping guns. I replaced all 4 coil packs, plugs, and wires. Ran fine afterward. Not sure what it was and still dont care. Figured 25 year old packs had well paid for themselves. Good Luck!

[richcraft]

Got the 140 running in the driveway last weekend. Ran like *****. I pulled the carbs and rebuilt them. Still ran like *****. I changed the fuel pump being 30 years old and it ran sweet. I took down to the river and could only get 45 mph out of it. On the second pass the motor quit. I pulled the plugs out and found melted aluminum on them. Paddled back to the launch and brought the boat home, p*ssed of course :mad:. Pulled the heads off and found 2 melted pistons on the port side.
Anyone know what would cause this? My guess is high speed jets are plugged or the reeds are stuck. My buddy is not high in the maintenance department and left gas in it over the winter. I did put new gas/oil before the test.
Motor is firing on all 4.

Thanks

[flabum1017]

Can you post pictures...... where did the pistons melt on top or on the sides?

[richcraft]

Right on top, sides are fine.

[flabum1017]

Ran lean....... not enough fuel. Sounds like the carbs need to be cleaned better. Did you pull the jets and soak the carbs when you cleaned them?

Could also be a fuel system restriction or air leak.

[EMDSAPMGR]

Some things to check. I'd pull the 2 port high speed jets in each carb and check for debris in them. Could be some dirt restricting fuel. That will cause a lean condition. Could also be that the failed cyls did not get cooled well. Since the failure occurred on one side, that could be related to the fact that each thermostat cools one side of the powerhead. Possilble that the port thermostat is stuck or that the port pressure relief valves did not function properly and restricted the extra water flow when on plane. If they every got overheated, they will deform and not function as designed. Check the condition of the water diverters in the block. If they are missing or misplaced, they can cause piston failure. You'll need to know what caused the failure before (if) you decide to rebuild it again.

[wrechin2]

I have a 150 merc here now that melted a piston and damaged some of the other ones. Found the culprit was water in the fuel. Water is heavier and thicker than fuel and will not pass through a jet as fast and will cause a engine to lean out. When I drained the carb it was full of water. Guy had a sock for a fuel cap!!!!!

Did you get all the old fuel out??? Just a thought. After you get the engine repaired it is very simple to have a repeat failure. On all the rebuilds I do, I remove ALL the fuel. Just a thought and a suggestion......

EMDSAPMGR,
Got that modified X-flow to pull a 25 4 blade to the limiter. Hole shot still sucks!!! Thanks for your help on it....

[richcraft]

Thanx Men,

We have another rebuilt 140hp powerhead we are going to put on. I will definately pull the thermostates and replace. And definately go through the carbs more thorough. When I ran the motor in the driveway the heads did not get hot and seemed to be equal temp from one side to the other. Gotta be the high speed jets.
Anyways, I put buddy's boat off to the wayside cause I just got my 175hp Looper back together. I am putting on my 20' pontoon boat. Repowering from a 90hp. Can't wait to try it. I built the boat myself and am adding a center toon with lift strakes. Will post pic's when I getter done.

Thanks again.

[flabum1017]

Overheating would have scuffed the skirts, running lean melts the tops. Check the entire fuel system for leaks or restrictions too.