[heritage03]

Got a 25 hp 4 strk Mariner and it runs great, starts and runs on low speed just fine. When I go to throttle up it will stall. If I ratchet the throttle a few times it will catch and run wide open as long as I leave it there. When throttling back if too fast it will stall. Always starts right up. Had carb off twice and sprayed choke cleaner through all openings, jets are clear.
Fuel is clean I'm wondering if I have a timing advance problem.

[CharlieB]

The 4 stroke carbs have a small accelerator pump, yours may have a faulty piston seal or check valve, not pumping/squirting adequate volume for a rapid throttle opening.

With the engine turned off, remove the air box from the front of the carb. Disconnect the throttle cable, while watching down the carb throat, open the throttle completely. Can you observe the accelerator pump squirt lasting the duration of time that you were opening the throttle?

Did it squirt or dribble?

If it fails this test then you need to remove the carb, clean completely, and pay particular attention to the accelerator pump assy.

[heritage03]

I did check out the accelerator pump while the carb was disassembled and it pushed gas out seversl holes however I didn't check it as you described. Will do at earliest chance, (better weather).