So, I've been fooling around with this motor for a couple of weeks. 1976 Johnson Stinger 75 hp longshaft. The motor would start out okay, then after a minute or so, it would bog down.
I checked compression, rebuilt the carbs, rebuilt the fuel pump, adjusted all the linkages, put a new water pump in, put all new fuel lines in, put in new plugs, pulled the flywheel and inspected the timing base, looked at all the wiring. I've had it in the water a couple of times, and while there was some improvement, it would still bog down on WOT. I even hooked a timing light to it while on the lake yesterday to see if I had spark on all 3 coils. I had spark and still couldn't figure it out. Today, after adjusting linkages, I went fishing with my stepson. The boat ran worse than it did yesterday, before I put in a new high speed jet in the #1 carb. I pulled into a calm cove, and while my stepson fished, I took off the motor cover and the air silencer. I fired up the motor and BINGO, she ran with no problems. I took her for a spin, opened up the throttle and she sounded like a small block Ford with a 4 barrel. At first I thought she hadn't been getting air flow, but then I realized that EVERY time I put the air silencer back on, I was putting pressure on the fuel line to carb #3, as well as the main fuel line, thus restricting the fuel flow. TOO SIMPLE.
That's it. Problem solved. I wonder how many similar "bogging down under WOT" could be due to restricted fuel flow from the air silencer.
I checked compression, rebuilt the carbs, rebuilt the fuel pump, adjusted all the linkages, put a new water pump in, put all new fuel lines in, put in new plugs, pulled the flywheel and inspected the timing base, looked at all the wiring. I've had it in the water a couple of times, and while there was some improvement, it would still bog down on WOT. I even hooked a timing light to it while on the lake yesterday to see if I had spark on all 3 coils. I had spark and still couldn't figure it out. Today, after adjusting linkages, I went fishing with my stepson. The boat ran worse than it did yesterday, before I put in a new high speed jet in the #1 carb. I pulled into a calm cove, and while my stepson fished, I took off the motor cover and the air silencer. I fired up the motor and BINGO, she ran with no problems. I took her for a spin, opened up the throttle and she sounded like a small block Ford with a 4 barrel. At first I thought she hadn't been getting air flow, but then I realized that EVERY time I put the air silencer back on, I was putting pressure on the fuel line to carb #3, as well as the main fuel line, thus restricting the fuel flow. TOO SIMPLE.
That's it. Problem solved. I wonder how many similar "bogging down under WOT" could be due to restricted fuel flow from the air silencer.