1984 Johnson 150 GT, no power at WOT...

[HVACRat]

This is a 1984 Empire hull with the afore mentioned motor. I have owned this boat for 4 years, the powerhead was rebuilt 6 years ago. I bought this boat from the second owner; the first owner was Texas Parks and Wildlife, it was a Game Warden boat. The VRO had been disabled before I bought the boat, I pre mix the fuel at 50:1 and it has never had anything but synthetic 2 stroke oil since the rebuild.

I have never had a second's worth of trouble out of this motor and it absolutely flies when working correctly.

Time before last when I had her out I had trouble with it running well at WOT, I found what I thought to be the problem; some pretty seriously degraded fuel lines. I replaced the fuel lines from the tank (midship) to the motor, including a new filter. Vent line seems to be fine.

However, when I had it out this weekend it was even worse; it didn't just not run well at WOT, but it didn't want to run at all (really boggs down) and would stall at WOT. It idles (not in gear) fine, or as fine as it always has anyway. The idle has always seemed a little rough to me, but it will idle for hours if I let it without popping, coughing or stalling. It starts fine, pump the bulb, prime the carbs, starts right up. Pumping the bulb when under way, at idle speed, does not seem to help either.

I've read a few things from Google searches, but wanted to tap the true brain trust and see what y'all had to say. From what I've read it sounds like I should replace all the fuel and vacuum lines under the cowling, rebuild the carburetors and change the spark plugs. I'm sure one of those is the cause, but I'm no mechanic.

What would you look for, what do you think is causing this and what do I need to do to get her back in shape.

 

[jakedaawg]

Start with a compression test, open air gap spark test at 7/16", and a fuel sample into a clear jar....Report back results.

 

[HVACRat]

Start with a compression test, open air gap spark test at 7/16", and a fuel sample into a clear jar....Report back results.

Roger that, what do I do with the fuel in the jar? Send it somewhere...?

 

[jakedaawg]

Just look at it, make sure it looks like gas and is not cloudy or phase separated.

 

[boobie]

See if there is any water in it. Water will go to the bottom after sits for awhile.

 

[HVACRat]

See if there is any water in it. Water will go to the bottom after sits for awhile.

Sounds good. I will get he tools tomorrow and report back the findings.

 

[HVACRat]

Compression results:
Port side, top to bottom
80
85
83

Starboard side, top to bottom
90
90
90

Spark:
Port side, all spark across the gap, but I don't know if it is weak or not, but they all spark.
Starboard, no spark at any of the plug wires.

Looks like I have a bad Power Pack? How do I test to be sure?

 

[HVACRat]

No fuel separation either, no water, not cloudy or anything. It does look like the wrong color though. It is a kind of dark amber, like iced tea, maybe not that dark. I expected it to be tinted blue due to the oil but I don't really know. The fuel isn't that old, it had half a tank left from February and I added half a tank this weekend.

 

[HVACRat]

Also, spark plugs are crap. Starboard side are really rusty on the outside, port seems fine. The color of the plugs on the inside is very different from port to starboard. Port, which has the operational spark, seems to be cleaner than the starboard side; all of those look very dirty and black. New plugs are a must, might as well get new wires as well, I'm guessing that if the plugs are that rusty it might have effected the plug wires as well.

 

[boobie]

Your spark has to jump a 7/16 " open air gap on a spark tester. Does it ??

 

[HVACRat]

Your spark has to jump a 7/16 " open air gap on a spark tester. Does it ??

Yes, on the port side cylinders, but nothing on the starboard side cylinders.

 

[boobie]

Check the shift cut out switch to make sure it's not grounding out the cylinders. If that's okay go to cdielectronics.com for trouble shooting.

 

[HVACRat]

Check the shift cut out switch to make sure it's not grounding out the cylinders. If that's okay go to cdielectronics.com for trouble shooting.

I've looked all over this dang thing and can't find anything that resembles a shift interrupter switch and I can't find any reference to one on this year model, looks like I need a manual.

What is the best place to get a good manual, a good manual I mean, for this specific motor (if that is even possible).

 

[jakedaawg]

Switch packs from one side to the other and see if problem moves.

 

[jakedaawg]

Also check blk/yel wire for short to ground.

 

[boobie]

Sorry for the mis-information. There is no shift cut out switch on that motor. You may have a bad pack. Try E-Bay for a factory service manual.

 

[HVACRat]

Sorry for the mis-information. There is no shift cut out switch on that motor. You may have a bad pack. Try E-Bay for a factory service manual.

7hanks, I thought I was going crazy or something. I'll try ebay for the manual.

jakedaawg, I will try both of these if I get home before dark tonight.

7hanks for the help.

 

[HVACRat]

I just changed both packs, now I have spark everywhere! I will get her out on the water tomorrow for the real test. Thanks for all the help everyone! Happy boater again; dove, ducks and deer had better be on the lookout!

 

[trailking82]

From the initial comment of degraded fuel lines, leads me to a carb rebuild. Hose could have started degrading during you WOT run and clogged the highspeed side. OMC rebuild kits are about $30 here on iboats... if it hasnt been done yet in all these years it couldnt hurt the problem any more.

 

[HVACRat]

The water test went great on Saturday; she runs like a champ again. Thanks for the help!