Timing adjustment 1986 70 HP Johnson

[midsized johnson]

How do you keep the timing advanced but back the throttle adjustment off? The engine runs great in the water, idles around 1000 rpm. However, the idle is pretty high, 1400 rpm at idle on the earmuffs in the driveway. All the adjustments got out of whack when I replaced the lower unit. Long story, but I had an older style lower unit which required a different linkage than the newer one I replaced it with. I had a guy come over and adjust everything, but it wouldn't run with back pressure in the water. I upped the idle to 1400 and it does great in the water. Shouldn't I be able to back the idle back to closer to 1000 rpm's on the earmuffs and still fire in the water?

 

[Anchor Marine Repair LLC]

Re: Timing adjustment 1986 70 HP Johnson

A 2 stroke will always idle faster on muffs vs in the water. It's because the big change in back pressure (from none to alot)

As far as your question, I'm not following you. Idle TIMING on that motor is about TDC +- 4 degrees. At that speed, your carb throttle linkage cam follower should not be touching the cam.

In gear idle spec is about 800 RPM, in the water. If this doesn't all cooperate, then there's something not right. It could be just adjustment to sync/link or it could be a fuel, ignition, compression issue.

Here's a link to your motor's manual. The timing or sync/link is a good place to start.

Boatinfo - 1973-1991 Evinrude Service manual

 

[midsized johnson]

Re: Timing adjustment 1986 70 HP Johnson

A 2 stroke will always idle faster on muffs vs in the water. It's because the big change in back pressure (from none to alot)

As far as your question, I'm not following you. Idle TIMING on that motor is about TDC +- 4 degrees. At that speed, your carb throttle linkage cam follower should not be touching the cam.

In gear idle spec is about 800 RPM, in the water. If this doesn't all cooperate, then there's something not right. It could be just adjustment to sync/link or it could be a fuel, ignition, compression issue.

I can't see how to adjust the throttle without advancing or backing off the timing. I've got the factory manual, but it doesn't explain the throttle linkage/timing set up in a way that a non-mechanic like me can understand. When I tried before, I adjusted the cam back, but I don't see how, or even if, that affects timing. I don't think I can make it idle at 800 rpm in the water without retarding the timing too much for it to run.
What I'm wanting to do is keep the timing where it is and back the throttle off a bit. Before the lower unit and linkage switch, it started with just a bump of the key, now it acts like it's cold every startup even after a full throttle run. I get it going then it runs fine. Fires in the driveway like that, just a bump of the key. I feel like it's something I'm missing in the adjustments somewhere.

 

[TLL]

Re: Timing adjustment 1986 70 HP Johnson

Idle speed is adjusted by advancing/retarding idle timing. It is not adjusted by opening or closing the carburetor throttle plates. The carburetors throttle plates must be all closed at idle speed. The throttle cam should be close to but not touching the carburetor linkage roller.

 

[midsized johnson]

Re: Timing adjustment 1986 70 HP Johnson

Idle speed is adjusted by advancing/retarding idle timing. It is not adjusted by opening or closing the carburetor throttle plates. The carburetors throttle plates must be all closed at idle speed. The throttle cam should be close to but not touching the carburetor linkage roller.

So if I advance the spark until the cam hits, then back it off of the linkage roller, will that work?

 

[TLL]

Re: Timing adjustment 1986 70 HP Johnson

You should be able to achieve proper idle speed before the cam hits the roller. Throttle pickup timing (when the cam hits the roller) should be approximatly 4 deg ATDC. To adjsut the pickup timing change the lenghth of the rod by loosening the locknut and turning the knurled nut. The goal is having correct idle speed without having the cam hitting the roller.