Old 25 Johnson -motor idles fine but from half throttle and up it’s like it’s not getting fuel or choking out. I’ve never let it cut of completely. When I’m running over half throttle it will slow and speed up over and over untill it works itself to an idle.
I have rebuilt the fuel pump,replaced most fuel lines including line from tank to engine. I have not replaced tank itself or spark plugs.i have however inspected both but didn’t see anything wrong with either. Oh also pulled off carb and cleanedit.
Sounds like you’re starving for gas. Is the tank vented or is it just pulling a vacuum on it. I’d make sure that’s not the problem before going any farther. Open the crack open the fuel cap next time this happens and see if it helps. Have also had same problem from primer bulb, but I assume you already replace it with the fuel line. Also quick connect fittings won’t open up they are basically check valves if they don’t seat properly and are inexpensive to replace
You said old 25hp Johnson,what tank are you using? I had a 91 15 hp that did basically the same kinda thing. Up to around half throttle it was fine but after that it would start surging and bog down. After new hose set and everything it still did it. Had the metal tank that came with it. Don’t remember why but I took the connector assembly off the tank and found the copper or brass tube was cracked. Switched to the plastic tank and a few years later the plastic pickup tube on it did the same thing.
That sounds like it! I have a plastic tank with all new fittings. I’m going FTP replace the fuel intake clip on the motor today and see if that works. Thanks