uggghhhh........

[olazabel]

1978 mercruiser 470 with mc1 drive.

I Spent a bunch of time replacing the lower shift cable, gimbal bearing, and bellows this week. Got lots of good help from this forum along the way. I Finally got everything back together, got the shift cable adjusted (i think).

Had the boat idling in the driveway for about 20 minutes with a tach on it. Right around 750 rpms, sounded great, and I was already thinking about getting out on the lake tomorrow, and then.....

All of the sudden the idle jumped up to about 1400 rpms and it won't settle back down. I tried shifting it in and out of gear a few times thinking something was stuck, but it stayed up around 1400. When this happened I had the spark arrestor off of the carb. Is it possible that something fell (or flew) into the carb and caused this to happen?

Any other ideas about what the heck happened?

 

[olazabel]

I just replaced the lower shift cable, and shifted the boat from neutral to forward, to reverse, etc. several times to make sure the cable was adjusted correctly.

Each time, everything worked great, And then the last time I shifted it into gear, I revved it up to about 1200rpms, then back to neutral, but the rpms never dropped back down.

 

[Blueghost924]

Remove the throttle cable from the carb and see if that clears up the problem.

 

[olazabel]

will try that first thing in the AM, and let you know what happens

 

[olazabel]

took the throttle cable off the carb, and when I pushed down on the linkage could get the idle to drop, but not down to normal, turned the plastic barrel on the throttle cable away from the carb a few turns and it helped.

then I realized the butterfly in the carb probably wasn't closing all the way, held it wide open, sprayed a bunch of carb cleaner in, started the boat and the idle dropped some more. this all started while the boat was running with the spark arrestor off, so i was thinking jome junk wight have fallen in and kept the butterfly from closing all the way.

the idle is still around 900-950 rpms now on muffs, while it was at 750 or so last night.

also the engine is running a little rough now almost sounds like its missing.

now wondering if adjusting the barrel on the throttle cable could change the shift interrupter setting at all?

 

[Rick Stephens]

First thing is get the motor running smoothly at the right idle RPM. Too high idle is hard on gears. Then work on cables and linkage.

 

[olazabel]

Thanks Rick. Makes sense. What is a good initial setting for the idle mixture screws on the rochester 2 barrel carb?

I've been looking online, and have seen posts recommending everything from 2 1/2 turns out from seated to 1 1/4 turns out.. as an initial setting

 

[Rick Stephens]

Doesn't matter what the initial setting is as long as the motor will start. They get changed to suit the motor anyway, so just pick one. Then follow the Mercruiser Service manual and adjust them to a proper setting. Make sure points contacts are perfect. Set the dwell.