Hello I have a 18hp mercury two cylinder single carb engine. When I'm at WOT the engine loses power after running for about one minute. it drops to aproximatly 70% power and stay there consistently. When I back off the throttle it will regain full power for that given throttle position. this problem is very consistent.
Things i've tried:
1. fuel is high octane and new
2. the fuel pump is good and tank properly vented (hose ball stays hard at WOT and pumping it does nothing).
3. carb is clean and adjusted perfectly for idle.
4. adjusted timing advance rod forward and back but the original position ran best
5. fixed all fuel and air leaks on the engine and carb
6. spark plugs are new and look mid-dark brown (possibly slightly rich)
7. cylinder heads have some carbon buildup but nothing excessive (possibly running rich).
8. exact 50:1 fuel mix in tank
Things i've tried:
1. fuel is high octane and new
2. the fuel pump is good and tank properly vented (hose ball stays hard at WOT and pumping it does nothing).
3. carb is clean and adjusted perfectly for idle.
4. adjusted timing advance rod forward and back but the original position ran best
5. fixed all fuel and air leaks on the engine and carb
6. spark plugs are new and look mid-dark brown (possibly slightly rich)
7. cylinder heads have some carbon buildup but nothing excessive (possibly running rich).
8. exact 50:1 fuel mix in tank