Tuning a 2 stroke with single pilot screw?

[Tim Good]

Summary: I think I need to tune my 5hp as it lacks power compared to previously. Can you recommend how I can tune with just a single pilot screw?

Long Story:
I have a 5hp yamaha. Couple of months ago I disassembled the carb to clean it after the mesh filter collapsed in the fuel tank.

Stupidly I didn’t take a note of the pilot screw (mixture) position. I’ve tuned it the best I could using YouTube videos with the pilot and the idle screws but it feels like it is perhaps 80% power of what it was. You’d never know with just one person but with two of us previously we could plane in our dingy quite easily. Unknown what you’re thinking.... you’ll never plan with two people and a 5hp but we’re both very light and we could.

The only other thing that has changed is the inclusion of an inline fuel filter-between the and carb.

Could it be average fuel? Would high octane fuel make the difference? The fuel is only about 8 weeks old.

 

[Caraway]

In a word. No.
The pilot screw allows you to get the air/fuel mixture correct at low revs. The full power mixture is controlled by the jet. Perhaps there is some blockage. Modern fuel is awful for leaving jelly-like deposits inside the carb. A soak in carb cleaner and a good blow with an air line helps to clear the passages and jets. Jets can be poked out with SOFT wire. You don't want to be opening the small orifices up at all.

 

[VicS]

The pilot screw will not have any significant effect at high throttle openings

To adjust it set it at 1.5 turns open from gently seated .
Slow the rpm to a minimum. Gently screw the pilot screw in a fraction of a turn at a time , reducing the rpm if necessary , until it falters. Then back out the screw until the engine runs smoothly. Finally adjust the idle rpm
clean the main jet and passages again as suggested above before attempting to adjust the pilot screw.

use a soft copper wire or nylon monofilament fishing line to clean jets.