Engine wont return to idle speed

[Tommy c]

We've got a 40hp 2 stroke that starts up and idles lovely.
It revs up really responsive too.
The problem is it won't fully return to it's idling speed when throttling off and idles at a speed far too high to engage gear.
All the fuel line, filter and carb are spotless.
Has anyone got any ideas where the fault could be?
TIA

[User name]

Might the butterfly valve be sticking open slightly? If you push directly on the linkage, does it go back to normal?

[Tommy c]

Originally Posted by User name

Might the butterfly valve be sticking open slightly? If you push directly on the linkage, does it go back to normal?

Haven't tried anything yet other than clean the carb etc.
If it returns to idle speed if pushing on the linkage, is it just a matter of cleaning to rectify

[Peter_C]

Disconnect the throttle linkage inside the cowl and see if you whack the throttle open and gently open it if it still sticks. That will tell you if it is the throttle side (in the tiller?), or carburetor side.

Possible the carbs just need to be dialed in. Syncing them and adjusting mixture is not always the easiest thing to do, but how much more can you screw up?

[Fenlander]

Tommy I forget what is your setup, remotes I assume?

[Tommy c]

It's currently on tiller

[User name]

Originally Posted by Tommy c

Haven't tried anything yet other than clean the carb etc.
If it returns to idle speed if pushing on the linkage, is it just a matter of cleaning to rectify

Possibly cleaning, but also burrs or damage on the plate itself can cause it to bind. It can also be down to improper adjustment, or issues further up to the tiller. If it returns to correct idle by pressing on the linkage then that tells you that the the issue is either at the butterfly, or external to the carb (linkage, cable, throttle grip etc etc).

[smallribber]

Does the tiller friction throttle adjuster need some oil

[Tommy c]

Originally Posted by User name

Possibly cleaning, but also burrs or damage on the plate itself can cause it to bind. It can also be down to improper adjustment, or issues further up to the tiller. If it returns to correct idle by pressing on the linkage then that tells you that the the issue is either at the butterfly, or external to the carb (linkage, cable, throttle grip etc etc).

Well it's going to be used on remotes when it's finally fitted to the boat so I'll remove the tiller now to eliminate that side of things then.

[Tommy c]

Just been out for a quick look.
Without starting it up, the butterflys open and fully shut with the tiller.
I'll try and load a video of it later.
It's obviously getting extra fuel at idle after delivery throttling

[Fenlander]

Yep a video and/or pics would help.

Are you totally sure the throttle butterfly is fully at its closed position, it only takes a small amount open to cause this.

Other than that I'd be thinking an air leak.

[Tommy c]

Originally Posted by Fenlander

Yep a video and/or pics would help.

Are you totally sure the throttle butterfly is fully at its closed position, it only takes a small amount open to cause this.

Other than that I'd be thinking an air leak.

Air leak from where

[Fenlander]

Anywhere that can allow air into the carb/inlet. Such as worn butterfly spindle or the carb body where it goes through.

Is this a new to you outboard that's turned out to be like this from your first start, or one you've had ages and it's just stated doing it?

[Tommy c]

Originally Posted by Fenlander

Anywhere that can allow air into the carb/inlet. Such as worn butterfly spindle or the carb body where it goes through.

Is this a new to you outboard that's turned out to be like this from your first start, or one you've had ages and it's just stated doing it?

It's actually my son's but yeah it's a new to him outboard.
How do I go about trying to find a possible leak?
The motor looks like it's done nothing inside or out

[Fenlander]

What make and year is it?

[Tommy c]

Originally Posted by Fenlander

What make and year is it?

3 year old parsun

[Fenlander]

Is that a Yamaha copy?

[Tommy c]

I think so. The impeller is from the 6h4

[Tommy c]

I have noticed that the fuel filter on the engine, that's before the fuel pump, fully fills when primed but once the engine is running, is barely half full