Mercury 80 Thunderbolt idle speed

[fishdog4449]

How do I change the idle speed on a Merc 80, inline 4 dual carb?
I must be stupid or something, I've scoured the Clymer and nowhere does it say how to drop the idle RPM. This is my first Merc engine, i normally go with Rudes, I've looked all over the engine for a low speed adjustment screw or idle speed setting?
She stalls frequently when put into gear, and makes a pretty loud clunk as well. I'm fairly sure its idling too high.
anyone?

 

[hkeiner]

Re: Mercury 80 Thunderbolt idle speed

I would expect that the Timing and Synchronizing section (often referred to as link and sync) of the manual describes how to set the idle speed. Typically, the idle timing screw is adjusted so that the motor idles at the RPMs specified by the specs with the motor running in the water and in gear. I don't know if your particular motor is unique and requires a different method, but if it did I expect the shop manual's Timing and Synchronizing section would describe it.

Note that there are several steps (settings) in the link and sync. Each step (setting) is dependent on the previous steps (settings) being correctly done. It is usually a good idea to check (adjust) all the settings and to do so in the order described in the link and sync. Adjusting a latter step's setting to offset a previous step's incorrect setting can lead to problems.

 

[Chris1956]

Re: Mercury 80 Thunderbolt idle speed

Dog, The throttle cable pushes the throttle closed, up against the "Idle Stop" screw. To lower the idle speed, you back out the idle stop screw and adjust the barrel nut on the throttle cable, if necessary, to push the throttle closed.

Normally this is done as part of the "Link and Synch" where the timing is set, and the carbs are synchronized to the throttle and the idle mixture is adjusted.

 

[fishdog4449]

Re: Mercury 80 Thunderbolt idle speed

Ok, go the manual will try link and sync sometime this week.
Have a new problem, something is screwed up with ignition.
I had a really hard time getting it started yesterday. When it did it sounded like it was backfiring as it ran, definitly misfiring, wouldn't rev up, made a bad knocking / backfiring sound. I'm going to pull each plug in turn and find out which cylinder is bad. I think it may be a bad coil? Any suggestions???

 

[Chris1956]

Re: Mercury 80 Thunderbolt idle speed

Dog, I would do the link and sync first. Clams Canino posted a link and sync procedure for that. It may be under the FAQ portion of this forum.

If your timing is off, you could have the knocking and oter symptoms.

 

[fishdog4449]

Re: Mercury 80 Thunderbolt idle speed

Haven't done link and sync, tried running it yesterday and something is wrong with the number 4 cylinder.(runs fine with number 3 disconnected, so i don't think thats a timing problem) I think it may be the plug wire it is very corroded where it connects to the coil and it doesn't "click" onto the spark plug like the other ones, maybe a bad connection?
i have some plug wires laying around, put them into today just to be sure before i spend 40 bucks on a new coil

 

[hkeiner]

Re: Mercury 80 Thunderbolt idle speed

I suggest that you first confirm that the link and sync settings are correct before running the motor much more. If timing is significantly off, it can damage the motor.