Mercruiser 3.0L TKS carb rough idle

[The_Dude_Abides]

All, I have a number of questions about a rough idle problem that I'm having with my 2006 Mercruiser 3.0L with the TKS carb. The whole boat just shakes and a little bit of throttle fixes it immediately.

First, everything I've read says to use a shop tachometer to set the idle speed. What is a good shop tachometer? I looked on Amazon and the web and it seems like there are a lot of cheap ones that don't seem very effective. Do we use the one that hooks to the spark plugs or the photo ones? If you use the photo ones, where do you mount the reflective tape?

Second, with the TKS carb, it's my understanding that the TKS system increases the RPM initially. So, to set the idle setting, I should wait until the TKS unit is off right?

Third, do I need to remove the throttle cable prior to adjustment? I've been tweaking the screw some and it doesn't seem to really do anything right away. It seems like it takes a restart of the engine to register the change (if that makes sense).

Finally, I wonder also if the mixture is too lean or too rich. Once the idle speed is right, if it still shakes, I was thinking of setting the idle mix screw, but as is standard, the Mercarb has the cap. This one doesn't have a fully covered cap, but has a hole as shown in the photo below.

Is this compatible with the merc tool: http://www.cpperformance.com/p-62883...91-866201.aspx

Thanks
Justin

 

[Bt Doctur]

With a Dremel use a small disc and carefully remove the outer shell or obtain the special tool about 2 more turns should make it idle just right

 

[alldodge]

it's my understanding that the TKS system increases the RPM initially. So, to set the idle setting, I should wait until the TKS unit is off right?

Sort of but mostly, the TKS module provides more fuel (enriches) fuel during warm up. Once the module warms up it closes off the extra fuel.

do I need to remove the throttle cable prior to adjustment?

Maybe, and may help. Remove the cable and may even need to pull the throttle plate closed to make sure it is next to the idle screw. Once adjusted, then adjust the barrel nut and attach cable

I wonder also if the mixture is too lean or too rich. Once the idle speed is right, if it still shakes, I was thinking of setting the idle mix screw, but as is standard, the Mercarb has the cap.

Still shaking may be distributor, cap, rotor or timing and may not be the mixture. May even need a carb cleaning

Did the shaking just start?
Have fuel filter been changed?
Anything else which could help us figure out why this started?

 

[The_Dude_Abides]

Thanks for the replies. I went out on the boat today and I noticed that when idling after I turn off the engine (regardless of whether the engine is warm or cold) it is rough and is idling at 600-650 rpm ish. When I run the engine (e.g., go to any level of throttle) then go back to idle, it idles smooth, but at about 800 rpm.

I've only had the boat two summers now and it seems fine other than this. I just noticed the rough idle the past month or so. That doesn't mean that it wasn't going on before as this is my first boat and so I don't really know that much about them and so I could have assumed that was normal.

 

[alldodge]

The initial idle is a bit to low and may need to be increased, should be 700 rpm. The boat tach may be a bit off so the 800 may be closer to 700. Since it speeds up after some more throttle, you may just need to adjust the idle stop screw

Would need to know your serial number but check your timing
S/N 0L0970000 thru 0L340999 is 1 ATDC
S/N 0L341000 and above is 2 ATDC