1977 Johnson 70 hp bogging down with cowl on

[hatboat]

Hi all, I could use some help. My 70 hp 1977 Johnson outboard is bogging down with the cowl on. With it off, it performs well. I've had the fuel pump changes, impeller done and just added some sea foam which seems to have improved performance, but still with the cowl off. The carbs have recently been redone. The compression is 135, 132, 128 respectively. I'm assuming there is an exhaust leak but are they any quick fixes I can do to see if it does the trick. I'm not a boat mechanic and don't really want to sink more money into it.

One thing that I've noticed is that when I run the motor for an hour or so, it runs well. After that period, it bogs down and in some cases, stalls when I put it into gear. I'm assuming that this is due to it heating up (although it is not over heating).

On a side note, just behind the fuel filter, there is a little hole and gas is leaking out of it..it drips a little bit constantly.

Many thanks for suggestions and help.

 

[Bosunsmate]

Have you checked the air inlet on the cowl is clear?
Otherwise you will need to undo the powerhead and lift it up to replace the gasket unless that fuel dripping is making the air mixture in the motor too rich. Id sort out that leaking fuel first as that means air can also be leaking into the system

 

[hatboat]

Just checked the air inlet on the cowl and it's clear. Any thoughts on why the fuel filter would be dripping gas like that out the back?

 

[racerone]

Post a picture of the fuel filter !

 

[hatboat]

Thanks, see attached. It was just rebuilt about 2 weeks ago.

 

[Bosunsmate]

why was it rebuilt?
try tightening the screws a tad

 

[hatboat]

Thanks, this is what I did this morning. I checked the filter, the top right screw was a little loose, but all the others were tight. The center big screw was loos and was able to turn it twice. What I did discover was that one of the clamps on the center fuel line going into the filter was completely loose....I tightened that. It's still putting out some gas but near as much as it did prior to tightening it.

What's interesting was that I put the cowl on to try it and it worked. It planed nicely and got up to top speeds. Keep in mind that it was a cold engine. I did drive it for about 30 minutes, slowed down to idol, went back up again no problem. Turned off engine, sat for a bit, turned it back on and it planed and went up to top speed no problem.

Yesterday, I put seam foam in the gas and let it idle while revving the engine and lots of smoke came out. It seems to be going faster then it was before. There is still a little drip every 10 seconds or so from the fuel filter though. Here's my questions, did the sea foam have anything to do with the no bogging down with the cowl on or was it tightening the center screw on the filter and clamp? It seems to me the sea foam helped with the performance overall an has not bogged down yesterday afternoon or this morning...any thoughts?

 

[tblshur]

If I'm not mistaken the thing that says filter is the fuel pump , it being loose caused the bogging and carbines up the plugs which the seafom cleaned improving performance good job ! Now stop the leak ,may be fuel lines or cracked plastic barbs there is also seals on the back side of fuel pump I think maybe not.go to boats parts diagram and look up fuel pump and see. Hope this helps :joyous:

 

[hatboat]

Thanks for that. I'll check the lines, could be that. I did drive the boat some more with the cowl on and notice a bit of hesitation on the start up but soon opened wide up. This means that there is still a leak. What are the plastic barbs you're referring to? Thanks again.

 

[hatboat]

The gasket (number 2 in the attached diagram) was ripped around the center part, so basically 2 pieces. Could this be the issue?

 

[hatboat]

Replaced the gasket and there is just an intermittent drip from that back whole of the gas pump. What's weird now is that the bogging down at the beginning has returned with the cowl on. It bogs a bit then opens up again to full. Previously that but all disappeared. I'm assuming there is still a leak. Any other suggestions on what to look for? MAny thanks

 

[Bosunsmate]

was there a small gasket between the pump and the motor?

 

[racerone]

The 70 hp pump mounts on a bracket.---No gasket required on it !

 

[Bosunsmate]

so it runs ok at high rpm now? Maybe your link and sync needs doing to fix the bogging down at low rpm
and find the leak cause

 

[hatboat]

Update: Thanks all for your suggestions. The boat is operating like it use to so am very pleased (knock on wood). This is what I did. Ran seafoam and it improved performance. Found the leak at the top of the exhaust manifold, there were actually two, but in the same place. Did not want to replace gaskets because 1) would have to get a mechanic to do it, and 2) didn't want the boat out of the water. So what I did was take that JB Steel (puddy stuff) and placed it over the hole. It dried and did stop the leak. Not sure if this is a permanent solution and I'm assuming I need to replace the gaskets. Has anyone ever used that stuff for a permanent solution? The boat now runs with the cowl on and is like I remembered it. The fuel pump is still leaking out the back but I believe it's a diaphragm and that comes in tomorrow so I'll replace it then.