Mercruiser 3.0 choke/ idle issues

[Gino27]

First off i'm new to this forum so hope I did this right.

I have 2003 Stingray 180lx that is still in almost new condition. Two years ago I had stalling issues and fixed them with new fuel pump, fuel filter, and rebuilt carb. Since then it has run great but idled high. I had trouble getting the idle to be smooth at about 800rpm in gear and on the water. But in the process I had to increase the pressure in which the throttle cable pushed the throttle closed. Now the idle screw pushes against the idle cam so hard that the choke is stuck.

I know this is a lot but any help would be awesone. Thanks!

 

[Gino27]

I'll also add that it idle and runs fine at 1000rpm but it bangs and lurches into gear. Once at 1000rpm, one slight turn of the turn and the revs drop to around 600 and it knocks around like crazy. With the throttle cable disconnected it won't return to idle without me pulling it there.

This whole thing is frustrating because I know the boat is seaworthy for the first time in 3 years but I fear for damaging the outdrive with a high idle

 

[alldodge]

Sounds like you might need more work on the carb in the idle circuits. The channels in the carb are small and can get clogged easy.

Before that need to go to the basics, need to check timing and think it should be 1 degree ATDC (for serail numbers 0L341000 and higher) could use your motor serial number for verification.

The carb should be able to return to idle without the throttle cable, but needing a slight return pressure is acceptable. Needing more force says you need to find out why. Look at the throttle plates down the throat of the cab to see if the a centered in the bores. Some times they can be a bit off which can keep them from fully closing

Do you have a TKS carb or Merc?

 

[Gino27]

I have a Merc carb. My mechanic reset the timing already so I'm thinking that's not the problem. The throttle returns in it's own but if I push on the throttle lever a little more it starts to stall. It's like I just can't hit the sweet spot with the idle adjustment.

 

[Bt Doctur]

disconnect the throttle cable , start motor , get to normal temp, adjust mixture screw for highest idle, then adjust idle speed screw for the lowest idle . Around 700 ish on land.Reattach throttle cable with slight pressure on closing
If you cant do this you still have a carb issue

 

[alldodge]

My mechanic reset the timing already so I'm thinking that's not the problem

And it may be correct, but your mechanic should also be able to advise why the motor acts the way it does. Carbs are fairly simple devices, and the sweet spot (so to speak) is adjustable if its working correctly, yours appears to not doing so.

The idle mixture screws should be able to adjust if the rest of the motor functions are timed and working correctly. If the motor does not have a vacuum leak, has good compression, timing is correct, then the only thing left is the carb needs cleaned and adjusted

 

[Gino27]

disconnect the throttle cable , start motor , get to normal temp, adjust mixture screw for highest idle, then adjust idle speed screw for the lowest idle . Around 700 ish on land.Reattach throttle cable with slight pressure on closing
If you cant do this you still have a carb issue

I've tried that both in and out of the water and I can only get it down to 1000. If I try going any lower than 1000 it drops to about 500-600 and almost stalls. I've used both the in boat tach and a shop tach and they read the same.

 

[Gino27]

And it may be correct, but your mechanic should also be able to advise why the motor acts the way it does. Carbs are fairly simple devices, and the sweet spot (so to speak) is adjustable if its working correctly, yours appears to not doing so.

The idle mixture screws should be able to adjust if the rest of the motor functions are timed and working correctly. If the motor does not have a vacuum leak, has good compression, timing is correct, then the only thing left is the carb needs cleaned and adjusted

Just to make sure I'm making the right adjustments the idle micrure screw is the brass one on the side and the idle speed screw is the one that contacts the fast idle cam. Are there any other adjustments?

 

[alldodge]

Just to make sure I'm making the right adjustments the idle micrure screw is the brass one on the side and the idle speed screw is the one that contacts the fast idle cam. Are there any other adjustments?

Correct and there are no other adjustments

 

[Gino27]

Correct and there are no other adjustments

Is there any way to bypass the fast idle cam so the choke and throttle are independent? I've worn out the cam so much that it no longer increases rpms at idle. I would later go into replacing it but for now I just want it to run.

 

[alldodge]

Marine carbs do not have fast idle cams, they just have a rotating choke cam which should move freely

 

[Gino27]

Marine carbs do not have fast idle cams, they just have a rotating choke cam which should move freely

I know for a fact that it's a fast idle cam. I have the carb rebuild instructions and that number 22 is labled "fast idle choke cam" I've disconnected the linkage and put a washer behind the cam so it stays put. Now the choke moves freely

 

[alldodge]

Were getting into labels only in a printed document. It may be called a fast idle cam in print, but it should not be able to do the task of increasing rpm

Auto's use fast idle cams so when cold and the peddle is depressed, the choke closes and the choke closing rotates a cam. The auto cam increases in size (so to speak) so the idle stop screw is stopped further away and thereby increasing the idle rpm.

Marine has the same parts but the choke cam does not increase in size when its rotated. So if the choke closes the idle stop screw will be in the same spot as if it was open. If more rpm is needed for warm up the throttle only mode is used.

If the cam on your carb does increase the idle high when the choke is closed then the carb was assembled incorrectly with the wrong parts, or it is an Automotive carb.

 

[Bt Doctur]

#26 is what set the idle speed

 

[Gino27]

So I got the boat out to lake today and it ran like a dream. Idled smooth right at 700 in gear and very snappy acceleration. I'm going to run the boat until I (fingers crossed never) have anymore carb trouble. Thanks for all the help