1988 Johnson 150GT Bogs down badly after 15 minutes

[dgoock]

I got this boat this fall and when we took it out it severely bogged down after 15 minutes or so. I was wondering if it is possible the charging system might not be working and the battery be discharging and there is not proper voltage for a spark? Can that cause this to happen?

 

[ONERCBOATER]

Re: 1988 Johnson 150GT Bogs down badly after 15 minutes

would suggest load test on the battery, if it is in good condition it should run the engine for a rather long time if the engine is not charging (i have driven V8 powered vehicles 60+ miles with failed alternators/generators without issue on a fully charged battery. what makes me curious is that most outboards I am familiar with have magnetos and don't need a battery after start up.

things that would be on my checklist include

Fuel tank vents, are they open, are they plugged. 15min of operation would create a rather large vacuum in a tank that was sealed, enough so that the fuel pump could not draw against it.
for that matter is the primer bulb flattening while in operation staying rock hard, or anything else.

Water stream, is the pisser (water indicator) working, and is it putting out a good stream when the engine is cold then slowing up as the engine gets warmer. I have found this easiest to read when at an idle.

how hot are the heads and block getting, perhaps you have blockages in the water jacket(s) that are causing it to overheat and lose power.

do you still have spark on all cylinders when the problem manifests it's self. could be a failing coil. loose connection heating up after some run time.

others will be more helpful i am sure, there are many far more knowing than I.
the more information giving regarding your problem the closer they can narrow it down.

Sean

 

[dgoock]

Re: 1988 Johnson 150GT Bogs down badly after 15 minutes

Thanks Sean. The other symptom I just found it that the wrong spark plugs were installed. The previous owner put them in just before we test drove it on the water. They were a much cooler plug. They were wet fouled when I swapped them out for the correct plugs. But I think the fouling was due to what ever problem we have and not the cold plug.

 

[ONERCBOATER]

Re: 1988 Johnson 150GT Bogs down badly after 15 minutes

15min to fouling would be pretty strange, were all the plugs fouled alike?
when you say wet i assume you mean fuel/oil foul rather than water, if water you have a bigger issue.

something i forgot to include as to possible issues, water in fuel (more of an issue with this ethanol crud they call gasoline now, and clogged fuel filter.

 

[metriccrescentwrench]

Re: 1988 Johnson 150GT Bogs down badly after 15 minutes

That engine should have a SLOW mode where if it overheats it limits rpm to around 2500 or so, and when SLOW mode kicks in it does indeed run like crap. However, if that's what happened you should have heard the alarm buzzer (unless it's been disabled) so I'd check to see if the alarm buzzer is working. At the top of each head is a thermal switch, each one has a brown wire going to the powerpack. With the keyswitch on (but engine not running) disconnect the brown wire and ground the end going to the powerpack, you should hear the alarm buzzer.

You didn't buy your engine from a guy named Frank near Savannah, GA did you? Ask me how I learned about SLOW mode and overheating.

 

[dgoock]

Re: 1988 Johnson 150GT Bogs down badly after 15 minutes

Fouling is not water, it is fuel/oil mixture. I think it is fouled because we had to go about 3 miles with it running very poorly. I don't think it was hot. I pulled the cover and it didn't seem to be hot. We also squeezed the fuel bulb to see it it was a fuel issue and even took off the cap to the tank to make sure it wasn't a vent issue.

I will check to see if the alarms are disabled. It was smoking a lot too. And it would surge every once in a while like it wanted to run, but then it would bog down really bad when we were coming back in.

The fuel could have been bad too. I put new fuel in the tank. I have bought a new permanent tank to replace the portable tank he had. I looked in the old tank and saw a leaf in it, so I know it wasn't good! But I ran it on a new portable tank I bought to check it out before I got the new tank and it did the same.

 

[emdsapmgr]

Re: 1988 Johnson 150GT Bogs down badly after 15 minutes

The slow mode feature came out when they went to the single power pack the next year- 1989. Yours does not have it. It is possible that you have an ignition problem-one spark plug may not be firing once the engine warms up. Weak ignition components tend to fail once the engine heats up to normal operating temps. Take the boat out on the water-when it starts to miss, pull the cowling and put an inductive timing light lead on each plugwire and see what the flashes in the gun tell you. The gun flashes will show misfires, no fires, weak firing. Best to check the spark when the engine is in gear under load. With an extra person, it's easy to do on the water and it's a simple test. If you find the spark is fine, then you can get into the fuel system.

 

[dgoock]

Re: 1988 Johnson 150GT Bogs down badly after 15 minutes

Thanks for the message. If the weather cooperates I will check that today. I have replaced the plugs and wires and rebuilt the carbs.