Carb single screw adjustment?

[Tim Good]

Question: how do you tune a 2 stroke carb which has just a single pilot a screw adjuster? How do I know if it’s too lean or too rich?

People say it takes only 1/4 turn adjustments to get it right but when I alter it by that much you can’t tell.

Background:
I recently cleaned my carb on my Yamaha 2 stroke 5hp after some issues. I’ve got it all running again and it feels great. But when I’m in the dingy with my girlfriend we’re barely able to get on the plane, whereas previously we could easily.

I fear I may not have reset the single pilot screw adjuster to where it was.

Before anyone says that a 5hp will never get two people on the plane then that’s just not true. We’re only lightweights and it worked just fine.

I’ve seen this video but it only explains how it works, not how to time it.

 

[TernVI]

If it's a pilot jet screw, it will probably have no influence at large throttle openings.
The carb in your vid looks like something off a chainsaw, most outboard carbs are quite different.

Screw it all the way in then back it out 1 or 1.5 turns is a common starting point.

 

[LONG_KEELER]

I think you can only adjust the slow running circuit on my Mariner 2T which I believe is
the same as the Yamaha.

As you say, seems odd because nothing else has changed. Is the travel on the throttle arm
open fully ?

 

[Mark-1]

I think this ^^^^^ is the video that helped me most, but as others say your problem is probably elsewhere.

I'm no expert but I think you need to take the carb off and give it a good deep clean and inspection and if that doesn't fix your problem take it off again and do it again even more thoroughly.

 

[Mark-1]

As someone else says, if it's the ubiquitous Mercury/Mariner 4hp or 5hp 2T which I thought the Yamaha was, then it's 1 1/2 turns out from lightly seated.