Johnson 1978 85 HP Running Issues

[Sobbleson]

Hello! I recently purchased a 1978 Cobia Charger that came with a Johnson 1978 Javelin 85 hp outboard and it’s giving me issues (as could be expected with the age). It’s been a fun restoration project!

A bit of background since getting the motor:

1. I changed the water pump with a kit - motor pees now and doesn’t seem to have any circulation issues.

2. I replaced the throttle cable (was cracked and rusted). It wasn’t the same model number but the difference (I think) is in the connector end. I just rigged it up to work with my control box and it doesn’t have any issues pushing and pulling the wire.

3. I changed the spark plugs with the recommended one for the motor. 4 brand new plugs (less than 6 months old) and they all look wet with black oil when I checked them the other day. I wiped them clean and reinstalled. I have since rebuilt carbs (see #4 below) and tested the boat on muffs before going out on the water today. I plan on checking the plugs again this week to see if they’re all definitely sparking and how dirty they are now.

4a. This past week I cleaned and rebuilt the carbs with new gaskets and seals. For 40 years old, the carbs were extremely clean! No sludge and I only found 1 blockage (in the orifice plug at the bottom of the float bowl), but after some compressed air, it was gone. The float needle was not worn, but I changed it for the new one any ways. I soaked it all in carb cleaner for 20 minutes even though it was clean. Washed and let it dry. Reassembled and then I tested blowing in the gas connector to the carb and the float blocks it one way, but allows air when I flip it over. I reinstalled on the motor.

4b. I replaced the fuel pump with a new one. Old one didn’t have any blockages that I could find, but the diaphragm was a little warped. I managed to get the motor running well yesterday on muffs. I could turn it off and back on without any delay or issues.

5. My friend (who has been around boats since he was 14) has been helping me tune up the motor. We previously messed with the idle screw since we weren’t able to shift from neutral to forward or reverse without the motor turning off. We found a sweet spot on muffs where it can idle low and then change gear. When tested at the dock, the motor shuts off.

6. Today I got new fuel hoses that I’ll replace this week.

Which brings us to today…

Since I had it running well yesterday on muffs after the carb rebuild, we decided to test it at the dock today. I was able to get it started and it ran with the warm up lever all the way up - high RPMs. The motor seemed to be doing well, so I lowered the lever and played with the idle screw since it sounded like it wanted to shut off. I got it running, a hair higher than as slow as it could before turning off, for about 8 minutes and then it sounded like it was running out of gas and then shut off. There was still gas in the portable tank, I even held it so there was definitely gas at the withdrawal, and then I tried restarting it but couldn’t get it to stay on longer than 15 seconds. The gas bulb was tight. I noticed some gas was leaking out of the carbs when I choked it (it does that every time I choke it, so I assumed that’s normal). There’s a small connector at the bottom of the air silencer plate that seems to also leak fuel in the space between the air silencer plate and the carbs. We finally gave up and went home.

I know that’s a lot to read and I’m probably leaving out some info. We’re going on a camping trip in 2 weeks, so I’d love to get this figured out by then. I appreciate all the help I can get!

[Sobbleson]

Update: I unscrewed the spark plugs and they didn’t look really any dirtier than when I cleaned them the other day. Wiping them did reveal some black oil on the rag though. I plugged them in and started the motor. From what I can see, all 4 are sparking normally and in the center of the gap (not off to a side or behind it). I am tempted to rule out spark plugs as a culprit, but I can’t find my multimeter to test the ohms.