1972 Fiberform OMC120 I/O Idle Issue

[Reread123]

Hi All, I have a unique problem that I'm hoping someone can chime in on... So, my boat is in fairly good shape for being a 1972, it just turned 400hrs. This boat has a very unique design, (helm-forward, stub-nosed, bull-nose, whatever you'd like to call it). I think it's cool.
Anyways, my boat has the binnacle mount, T-handle throttle box. I've used the boat 4 times so-far since purchasing it.
First time out- no problems, ran great.

Second time out- ran great all day, then towards the end of the day after throttling back from high speed, is wouldn't return to low speed idle, without moving the throttle back and forth, they would come back down to idle.

Third time out- ran great most of the day, then throttle began to get worse and wouldn't return to low idle, I actually had to pull the throttle cable back into position at the engine mount, and it still wouldn't return all the way. I could get it down to about 1000 - 2000 rpm. Not good for shifting, etc...

So, I thought it might be the cable itself, so I decided that I was going to take it out and give it a good lube, and see if that would fix it. Read the manual, and started to take it apart. After removing the binnacle mounted throttle box, I noticed that the "Idle Control Link" was busted. Fortunately, I was able to find another one on E-bay. (It will be here next week sometime...) In the meantime, I used plastic weld epoxy to put the old "Idle Control Link" back together, and it turned out pretty good! I reassembled everything, and adjusted the cable on the engine side, where it attaches to the carb, and everything looked good. So I took it out yesterday.

Fourth time out- ran great, except again after throttling back, it wouldn't return to idle. I could get it down to about 1000-1200 rpm in gear, and about 1500-2000 rpm in neutral. :facepalm:

OK, here's the kicker: If you shut the engine off, and then restart it, it idles fine, right at 600 rpm. Put it in gear and it goes fine, but again when you back off the throttle, it won't return to 600 rpm. This does not sound like a cable problem, since shutting the engine off, and restarting, brings the idle to where it needs to be...

Anyone have ideas? This boat is in good shape, and I don?t want to ruin it, I think I'll pull the cable and lube it anyways, but it sounds like there's more to this then that...

Thanks!

 

[Howard Sterndrive]

Re: 1972 Fiberform OMC120 I/O Idle Issue

OK, here's the kicker: If you shut the engine off, and then restart it, it idles fine, right at 600 rpm.

get someone to watch the linkage at the carb when doing this

some engines give a good shake as they shut down - like a wet dog - might be shaking the sticky cable

or maybe you have some linkage fallen off or flopping around on the carb (s)

 

[Reread123]

Re: 1972 Fiberform OMC120 I/O Idle Issue

Thanks Howard,
I think you may be onto something. Because when I shut it down at the higher idle speed, it does shake a bit. I'll pull the cable and lube it, and then do what you say. It probably needs a new cable after 40 years...

Thanks again, I'll update later.

 

[cr2k]

Re: 1972 Fiberform OMC120 I/O Idle Issue

Marine cables are NOT ment to be lubed. Any lube added will cause more drag on the cable. If the cable is stiff or tight it is worn internally and must be replaced. With that said have you tried something simple like a return spring on your carb linkage?

Throttle cable should be adjusted so there is very slight pressure on the arm at idle to ensure full return.

 

[projo198]

Re: 1972 Fiberform OMC120 I/O Idle Issue

I don't know what carb you have, but you might check the parts at the idle adjust screw.

On mine the choke rod wasn't there and the circular plate the idle screw sat against was free. It would swivel completely around and not let the idle screw go all the way down when letting off the throttle.

 

[Reread123]

Re: 1972 Fiberform OMC120 I/O Idle Issue

Hi All,
OK, so here's the update. I took the throttle cable out of the boat, and followed the instructions in the manual. Yes, it actually gives instructions on how to lubricate the inner wire in the cable. I used penetrating oil and a drill motor. Reassembled everything, and set the idle, and took her down to Lake Washington.
She ran better, but would slowly begin to idle up after throttling back. So, I readjusted the idle two or three more times, (after throttling back), to get it right where I wanted it. Then she ran fine. It returns to 600 ? 650 RPM after throttling back every time now.
-Oh, I don?t see a return spring on mine, and I don?t see one in the manual either, but I picked up a universal return spring, in case it starts acting up again. No problems with the linkage either...
-I ran the boat all last week at Lake Sacagawea in Eastern, WA, no problems with the idle there either.
Thanks for the input!