1988 Mercury 135 V-6 won't idle down

[guy858]

hi guy's.. setting the timing on a friends motor and it states to dis-connect the idle stabilizer ( white/black stripe ) wire from the outer switch box before setting the primary timing adjustment.. all that is fine.. did the carb linkage adjustment as well and total timing adjustment.. after hooking back up the idle stabilizer wire and running it, it idles at 1100-1200 rpms.. ( and the idle stop is correct and the adjustment also ) and then if I back off the primary timing adjustment and it will idle down.. I checked the timing first before I backed off the primary adjustment ( obviously it was getting too much timing at idle ) at it was about 6-8 degrees advanced ( granted its running at idle now and should only be about 2 degrees advanced more than cranking ? ) I'm pretty sure the idle stabilizer is only suppose to work IF the idle dips tooo low and will bring it up to about 500 rpms or so ? is the idle stabilizer bad ? it shouldn't be advancing if the idle is high enough ? I don't want to retard the timing and shouldn't have to ? and yes, the carburetor butterflies are closed completely.. any thoughts ? I'd surely appreciate it ! thanks, Guy

 

[Chris1956]

OK, idle pickup timing should be 0-9* ATDC. The throttle can be adjusted to retard the timing a bit more by adjusting the throttle cable to push the throttle closed, and adjusting the idle stop screw to allow this. I would think that would solve your issue.

 

[guy858]

thanks Chris.. it will idle down with the timing retarded.. one question I do have ? IF the throttle plates are completely closed off.. and they are, why won't it stall the engine ? cutting off all the air should do it.. it will on cars anyway.. Chris, I've been a automotive mechanic for 30 + yrs.. just don't quite understand why I can't idle down the motor other than retarding the timing.. its taking in air from somewhere ? shouldn't matter what the timing is ? I should be able to idle it right down with the carb butterflies ?

 

[Chris1956]

Guy, That is just the way the OB carbs are made, and how the link and synch is designed. You may see some holes drilled in the throttle plates to allow idle air to enter.

In the 70s, automobiles had an issue with "run-on". At that point the OEMs eliminated all holes in throttle plates, but used a solenoid to hold the throttle plates open a bit for idle air to enter. When the ignition key was turned off the solenoid retracted and the plates closed, killing the engine. Outboards have never had the run-on problem. All Mercs (as far as I know) use ign timing to some extent to control idle speed. It is less on the inline motors, though.