Idle Pickup Timing - 1989 70

[tedious]

I have a 1989 70 triple, early production with the non-adjustable carbs. The OMC manual has 2 different link and sync procedures; apparently there are 2 different throttle cams and there is a separate procedure for each, called "Method A" and "Method B." I have the cam that corresponds to Method B, so that's the procedure I use.

My question is about timing at idle. Method A tells you to set the idle pickup timing, but Method B says nothing about it. Is it fair to assume this is just a mistake in the manual? Seems like it's still something I should check.

Tim

 

[tedious]

Re: Idle Pickup Timing - 1989 70

Related question, kind of a academic - when I am adjusting the idle stop, what is that really doing? Per the manual, after each change to the idle stop, I'm supposed to readjust the cam follower so it's a tiny distance away from the throttle cam. So the carbs are still completely closed, no matter how I adjust the stop. Near as I can figure, all I'm doing when I adjust the idle stop is changing the idle timing. True?

Tim

 

[jtexas]

Re: Idle Pickup Timing - 1989 70

question 2: true, idle speed is all spark advance and no throttle.

If it's a seloc manual, it could be a mistake. I'm inclined to believe that the OEM manual would not be a mistake.

Set your idle speed (plus a couple hundred RPM on the muffs, then fine tune it at the lake), adjust the roller to hit the cam right on the mark, it'll be fine.

 

[tedious]

Re: Idle Pickup Timing - 1989 70

Thanks. The two methods described are in the factory manual for the 1989 70. Seems like the idle stop directly moves the timer base to set the timing, and then the geometry between the throttle arm and the carbs is controlled by both the idle pickup timing adjustment and the cam follower.

Unfortunately, this has all become more than academic - after a carb rebuild, and fuel pump replacement, the test run didn't go at all well. Reasonable idle, then bogged down and dies as soon as you put it in gear. Trying to get right on the throttle didn't help - still bogged and died. Hopefully something simple!

Tim

 

[mikesea]

Re: Idle Pickup Timing - 1989 70

when you rebuilt the carbs ,wer they dirty,is so,are you sure all passages internally are clean,did you make certain all jets are clean,the fact it runs then bogs and dies COULD mean carb(s) could still have issues.That said,have you checked for spark and compression in all cylinders.A dead cylinder could also allow eng to perform at idle but die at a load.

 

[tedious]

Re: Idle Pickup Timing - 1989 70

The carbs were pretty clean to start with, and I'm sure they're clean now. I turned the idle stop in to get to about 1000 RPM on the muffs, but I didn't redo the full link and sync. Maybe I should have - after re-reading the manual, they do say to readjust the cam follower after any update to the idle speed. I'm suspecting I'm opening up the carbs before the timing is advanced enough. Sound reasonable? I'm not sure how sensitive the idle stop adjustment is.

I think spark and compression problems are unlikely, as the engine was running pretty well at high speed before the carb rebuild.

Tim

 

[mikesea]

Re: Idle Pickup Timing - 1989 70

inproper timing could bog,do the sinc n link

 

[jtexas]

Re: Idle Pickup Timing - 1989 70

I find that I don't always have to adjust the cam follower after each idle adjustment, but it's prudent to check it each time.

Dies soon as you put it in gear, could very well be running on two cylinders, but could just as likely be idle speed is set too low.

If you're setting the idle speed with the engine running on muffs, add 200 to 250 RPM; for example, my idle speed in gear is 750, but in neutral on the muffs it idles at close to 1000. You can fine tune the idle speed with the boat in forward, tied to the dock or even on the trailer on the ramp. (if there's nobody waiting in line).

Cylinder drop test: motor idling on the muffs, pull momentarily then replace the spark plug leads, 1 at a time. Use an insulated or plastic tool. If RPMs don't drop dramatically, that cylinder's not making power. I'd do the spark test and compression test, because they're easy, and then you know for sure you aren't chasing a wild goose.

If your carbs have 3 jets, I can tell you that a cylinder won't fire if you crisscrossed the idle and off-idle jets, don't ask me how I know.

In my experience, dies when you put the hammer down (as opposed to bogging down and slogging along), generally is more likely to be link & sync -- carb throttles open too soon, before spark advance has moved up enough.

 

[tedious]

Re: Idle Pickup Timing - 1989 70

Thanks for the detailed response. My guess was the same - that the carbs are opening up before the timing is advanced enough. I wish I'd thought about that while I was still at the lake, but it didn't occur to me until I was driving home in a bad mood. Part of the learning process, I guess - don't skimp on the link and sync, especially since it's not that hard to do.

Tim

 

[tedious]

Re: Idle Pickup Timing - 1989 70

Well, egg on face for me. Several link'n'syncs and some bad language later, I found a piece of lint in the high-speed jet of #3 carb. Very, very tiny piece of lint, but apparently it was enough. Motor runs well now, so I guess the lesson is I need to clean up around my workbench...

Tim