Mercruiser 165 i4 high idle then run away.

[Someguyincali]

When I start the engine it idles between 1000 and 1200. Then it slowly starts to run away and goes up to 2000+. I have been trying to adjust the choke, and both idle mixture and idle stop screw.

https://youtu.be/TDShCI6bTF

 

[Scott Danforth]

You have an air leak. Pull the carb, clean it, then reinstall with new gaskets

 

[Someguyincali]

Shoot. I was really hoping I wouldn't have to do that. It was running fine despite the fuel mesh screen being nearly completely clogged. I suspect the person before me adjusted idle based on low fuel flow. When I cleaned out the screen the idle took off.

 

[Someguyincali]

Nope. Not a vacuum leak. I can not find instructions that make sense on how to set the idle on this carb.

 

[stonyloam]

There should be an idle set screw that rides on a cam on the port side of the carb, make sure the cam that the screw rides on is not loose. You set the idle mixture with the screw in the base of the carb. Turn it in until it seats (lightly), then out 1 1/2 turns. Run at idle, turn the screw in until it starts to stumble, then out till the rpm begins to drop, then back in for a smooth idle.

 

[Someguyincali]

The high idle cam screw raises the rpm when tightened. The idle mixture screw does nothing. I sprayed the outside of the carb and intake manifold while running and no change in rpm. Cannot get it to idle lower than 1200. If I leave it alone for about a minute the idle runs up to 2000. If I grab the throttle linkage and manually push it down the idle returns to 1200.

 

[achris]

Disconnect the throttle cable. It may be hanging the carb open. Once you have the idle right, adjust the cable to JUST apply a light pressure in the direction of closing the carb, and re-fit it.

Chris.....

 

[Someguyincali]

Disconnect the throttle cable. It may be hanging the carb open. Once you have the idle right, adjust the cable to JUST apply a light pressure in the direction of closing the carb, and re-fit it.

Chris.....

I just disconnected the throttle cable. The high idle screw is set just enough so the engine does not die off on me. The idle mixture screw still does nothing even all the way in. I did the spray check for leaks and found none.

 

[Someguyincali]

*Update* I finally had time to resolve this issue. I removed the carburetor and upon inspecting the throttle plates I noticed one was bent. Some stupid moronic idiot (me) put a screwdriver down the throttle body to hold open the throttle then closed the throttle. I managed to straighten the plate out and regained control of the idle with the mixture screw. Her her running perfectly again.

Thank you to everyone who put in the time to reply to this thread.

 

[achris]

.... Some stupid moronic idiot ....

Ya can't trust those stupid moronic idiots.

Glad you fixed your problem. Happy boating.

Chris.....

 

[sogood]

FWIW Doesn't the mixture setting have to be done at normal operating temperature with the engine under load, that Is, in gear, with the boat tied up/ secured?

 

[achris]

FWIW Doesn't the mixture setting have to be done at normal operating temperature with the engine under load, that Is, in gear, with the boat tied up/ secured?

NO! Boat needs to be UNSECURED... ie, you need two people to do the final adjustments.

You can set things close on the flushers and just 'tweak' it on the water though.

 

[sogood]

Thanks for the clarification, as I had definitely read on a forum , possibly here, that the boat should be tied up. Either way, under load.

 

[achris]

Thanks for the clarification, as I had definitely read on a forum , possibly here, that the boat should be tied up. Either way, under load.

Not here....

Here's the full adjustment procedure from the Mercury genuine manual. Note point 4, "With the boat in open water..." Also note the comment about not leaving the helm. Implying that the boat is not secured to a jetty...



Chris.....