1972 Johnson 65hp

[jay_merrill]

So, here's one for y'all.

1972 Johnson 65hp, 3 cylinder. It has been a strong runner despite its age. I launched for a 3rd day of SAR on a case the other day, but had to come back in because it was missing, and would "bog down" at anything over 1/2 throttle. The motor ran fine on the previous outing for about eight hours.

One of the coils was replaced recently but I was about to change the other two anyway, so I pulled them and took them to the OMC dealer to be tested. One was breaking up badly and the other had minimal problems. I bought two new coils and installed them.

On my first test run, the motor still skipped a beat every so often and wouldn't take throttle beyond 50%. Any attempt to advance beyond that point caused the motor to bog down, acting like it was either overloaded with fuel or starving for it.

When I came in, I hooked up my timing light and ran the motor with it attached to each of the spark plug leads, one at a time. All three indicated steady firing with no misses. At this point I started thinking in terms of fuel so I pulled the filter/water separator to see how it looked. There was quite a bit of water in it, but I didn't see any dirt.

Today I took it for another short run (a couple of miles) and brought the timing light. It still bogs down and won't push the boat more than about 8 mph at 2600 rpm. It usually tops out at about 5,000 rpm and 27 mph. The timing light test showed a couple of skips in the middle cylinder, but that problem didn't remain for long. Pulling the plug wires one at a time, and then running under load, suggests that all three cylinders are firing.

The motor is pumping plenty of water and the head is not excessively hot after a few minutes of running under a load. I did a compression test this evening and all three cylinders at great, at about 138 - 140 psi. I am going to pull the fuel pump screen in the morning to see if there is any junk in it and I didn't try to do a "squeeze the bulb" test while underway, because I was alone. The fuel pump is about a year old, having been replaced right after I bought the motor.

My gut is telling me that I have some junk in the carbs but I am wondering just how much could get past a transom mounted filter/separator and the fuel pump screen. I guess there is another part of me that just doesn't want to have to fool with the carbs - I know, dumb but I hate screwing with multi-carb setups.

Anyway, any thought y'all have will be appreciated.

 

[ezeke]

Re: 1972 Johnson 65hp

Have you tried running it on a different tank and fuel line?

 

[JB]

Re: 1972 Johnson 65hp

Need a mate to do this.

Try squirting a bit of premix into each carb when she is misbehaving.

 

[HighTrim]

Re: 1972 Johnson 65hp

I agree with JB and Ezeke that it is probably fuel delivery related. Try spraying pre mix in the carb throats, pumping the primer bulb, and choking it. If any of those tests even things out you will be better able to pinpoint the issue at hand. If none of these, as Ezeke said, hook up a remote tank to isolate further. Let us know what you find.

Joes test for coils works well.

(Magneto Capacitance Discharge Coils - Continuity Test))
(J. Reeves)
Check the continuity of the ignition coils. Remove the primary orange wire from whatever it's connected to. It may be connected to a powerpack screw type terminal, a rubber plug connector, or it may simply plug onto a small boss terminal of the coil itself.

Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground of the coil or the powerhead itself if the coil is still installed.

Then touch (still with the red lead) the orange wire if it's attached to the coil, or if it's not attached, touch the primary stud of the coil. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire. Poor or no continuity of a coil is one reason for s/plug fouling.

 

[jay_merrill]

Re: 1972 Johnson 65hp

I have run it on more than one tank. I also ran it during the two test runs on a tank of fuel from a different gas station. I'm going to take a look at the choke position shortly - I think I remember hitting the switch when the problem originally showed up, but I'm not sure. One thing that occurs to me now is that the butterflys may be partially closed because I don't think the motor would remain runnning if they were fully closed. That might explain reaching a point in throttle movement where the motor wants to fall off.

I have also run the motor on two different sets of spark plugs, with no difference in performance.

I also remembered something late last night after my original post, that may have me pointed in another direction. When the problem occurred I let the motor run for a bit to see if it would clear up but finally decided to return to the launch. By that time, I was a few miles out and, thinking that I had a cylinder that wasn't firing, decided to shut the motor down and go to my kicker, just to prevent wasting a lot of fuel. With only a 6hp pushing a 17.5 foot boat, the trip took a little while and the second motor ran fine all the way, on the same tank that the main engine had been using.

I think I will pull the fuel pump screen today anyway, just to see if there are any signs of junk. I was reading a PDF about filter/separator units last night that someone posted in another thread, and learned that the type that I have will bypass the filter if there is too much water in it. My carbs have drain plugs on them so, I think pulling them just to see what comes out might be a good idea too.

The ignition coils on the motor are all new at this point - two replaced as part of this exercise and one replaced about 2 months ago. I also replaced the powerpack about six months ago with one that I bought with a compete ignition system on EBay. It has worked well but it is used so no guarantees there. I looked at stator prices last night here at IBoats and can buy a CDI unit for $170, which I believe is a lot less than an OMC part. Powerpacks are about $100 and I think the CDIs are out of stock so Sierra would be the choice on there. Anyone have any comments about these units? Good? Bad? Better than stock?

PS: I just edited this to add a couple of things.

 

[HighTrim]

Re: 1972 Johnson 65hp

IF you find that the ignition system is to blame, I would of course get OEM parts,they are the ones that manufacture the motor, other than that, stick with the CDI over the Sierra. Before throwing parts at it though I would run the fuel tests as mentioned with the aid of a helper. The CDI page has good troubleshooting tips as far as the PP, stator, etc...

 

[ezeke]

Re: 1972 Johnson 65hp

One other possibility is that the original thermo switch is still connected or has been reconnected to the choke solenoid which could explain the erratic behavior.​

See if there are a purple and yellow wires running from the #8 post on the terminal block to the choke solenoid [edit] and to the thermo switch.​

 

[jay_merrill]

Re: 1972 Johnson 65hp

That's one I wouldn't have thought of - I will do that.

Time to get off of the boards and go do it!

 

[ezeke]

Re: 1972 Johnson 65hp

If you find that the thermo switch is connected to 6 and 8 on the terminal block, you may wish to disconnect the two wires and tape them off.

Then cross 8 and 7, from the solenoid so that full power goes to the choke solenoid from the manual switch on the remote.​

 

[jay_merrill]

Re: 1972 Johnson 65hp

Ezeke, the block is wired as you describe. When the ignition switch is turned to the on (run) position, thermo actuation of the choke occurs, with half deployment of the butterflys. Advancing the throttle then opens the butterflys back to a fully open position.

What has me curious now is that this throttle position is right about where the engine bogs down. It also runs pretty much as normal to that point. I am now wondering if the motor wants a bit of choke beyond the point that the butterflys have been forced open. We have had a couple of cold fronts blow through and the water temps have been chilly. If the thermostat is stuck open (I haven't checked at this point), do you think the problem might be that the motor is just running too cold? When I was fiddling with the timing light and pulling plug wires yesterday, the head was pretty cool to the touch after a few minutes of running at partial throttle. I didn't think anything of it at the time because I was more focused on making sure that I didn't have an overheat situation.

 

[ezeke]

Re: 1972 Johnson 65hp

In February of 1974, OMC issued Service Bulletin 1335, soft pedaling the issue of the thermo switch which caused more problems than it solved because it tended to engage the choke when it was absolutely not needed.

The choke solenoid had two positive leads which effectively gave you half a choke from the manual switch and half from the thermo switch. What works best is to get full power from the manual switch.

The 1973 70HP is wired about the same as yours, so you can follow the SB by wiring it that way. Click the thumbnail: The thumbnail is jpg, so use your photo software to enlarge it if you want.

 

[jay_merrill]

Re: 1972 Johnson 65hp

I'm going to give that a try and see what happens. I actually have a packet of jumper clips in my shop now so it ought to be pretty simple to do. Thanks for the info.

 

[jay_merrill]

Re: 1972 Johnson 65hp

I tried the change on the automatic choke feature but no improvement. That said, I think I am going to leave the automatic choke disabled for the time being. The exercise was worth the time, however, because it is just one more thing about the operation of the motor that I now have a better understanding of.

 

[HighTrim]

Re: 1972 Johnson 65hp

Did you ever try choking it out, spraying pre mix in the carbs, and priming the fuel bulb with the aid of a friend?

 

[jay_merrill]

Re: 1972 Johnson 65hp

I haven't tried the spray yet and didn't have anyone available for a squeeze of the bulb under way either, but I did run it today and tried the next best thing to doing that - I pulled the throttle back relatively quickly, put the motor in neutral and then "ran" back to the bulb to check it. The fuel pump seems to be working OK because the bulb was very hard. I also checked the screen in the fuel pump and there was no sign of junk at all.

Tommorrow I am going do an ohms test on the sensor coils and charge coils. And, if I can find a spark gap checker and neon test light, I will do those tests too. I am a great deal more familiar with the "pre-CDI" engines so these tests will be a good learning experience, while either eliminating some possibilities or confirming them.

Depending on what those tests reveal, I think the next thing will be to try the "squirt test." This motor has drain plugs on the fixed, high speed needle valves so I will probably get around to drainng each carb into a cup too. BTW, is there any way to clean out the carbs without completely disassembling them? For example, can I get the bowls off of them without pulling the carbs and disturbing the linkages, etc?

I suppose another possibility would be that the carbs and ignition have somehow gotten out of sync. I don't know why they would have but it might be soemthing to consider.

 

[HighTrim]

Re: 1972 Johnson 65hp

Not many neon testers around any more A DVA meter is what is used now, or you can get an adapter for your current multi meter, check ebay. I might also consider bumping the job of spraying the pre mix into the carbs higher on your list of things to do.

 

[jay_merrill]

Re: 1972 Johnson 65hp

Still haven't gotten around to the carb but did check the charge coils and sensor coils. Charge coils are right at 900 ohms, which is where they are supposed to be. Checking the sensor coils to ground shows infinity on all three (which it should) and sensors 1 & 3 show 8 ohms on the ohms check. They are supposed to be 8.5 ohms plus or minus 1 ohm. The number two sensor coil shows 12 ohms repeatedly and with multiple checks to make sure the meter was "zeroed out" prior to the tests.

It remains to be seen whether or not this is the source of the remaining problem but it is looks like it at least one of the problems.

 

[jay_merrill]

Re: 1972 Johnson 65hp

Had an interesting conversation with my OMC dealer today. His take on things was that the problem is probably ignition but could be fuel. I'll repeat some of his comments because they were very helpful and might solve a problem for someone else, even if they do not turn out to be my problem.

First, he said that sometimes the throttle plate shafts and/or carb housings become worn on older motors. When this happens, the motor will run fine until the vacuum in the carb reaches a high enough point to start sucking air in through the loose shafts. This disturbs the proper fuel air mixture because there is then more air present than the throttle position would normally allow. One of the ways to check for this is to smear some grease around the affected shaft(s), which will provide a short term seal. If doing that fixes the problem, its time for a new carb

He also said that an easy way to check for fuel delivery problems is to pull the "air horn" off of the carbs, get someone to drive the boat at the speed where the problem becomes noticeable and then use a timing light shining into the carb throats, one at a time. Apparently the strobe effect makes it very easy to see the mixture in the carb, especially if the problems are intermittant.

Its been pretty cold here for a couple of days so I am going to lay off until its a bit more pleasant. I'll update as I know more.

BTW, an OEM timer base for this motor is $357 dollars! YIKES! I think I will be buying that CDI unit that I saw!

 

[ondarvr]

Re: 1972 Johnson 65hp

Sounds like spraying premix into the carbs is easier and results in the same information, plus any body can do it for you.

Draining the carbs is a ten minute job, sometimes junk comes out and sometimes it doesn't, so if the gas is clean the jets can still be plugged. If the carbs haven't been gone through in a while, then maybe it would be a good idea to rebuild them even if they aren't the problem, it's really fairly easy to do.

 

[jay_merrill]

Re: 1972 Johnson 65hp

Yeah, you are right. As Hightrim said, I do need to do that. The carbs shouldn't need rebuilding because I had my dealer do that last February and the motor has been run frequently all year. If it turns out to be some garbage in one or more of the carbs, I'll just have to deal with it. I have rebuilt plenty of them so that part doesn't bother me - its the syncing of multiple carbs that I have no experience with. One option would be to do all of the work up to that point and let my dealer make sure the adjustments are right. Either that or find someone that I trust to know what they are doing show me. Actually, the latter option would be preferable because I'll be ready to tackle it next time.

Regardless, I probably will replace the remaining ignition parts over a period of time. I know that I have one funky sensor, and you can't buy them separately, so I'll have to buy a complete timer base. I surfed the net a bit for them and I have seen CDI units for as low as $227.

The stator is holding in there for now, plus I have another used one, so I'll wait awhile on that. Eventually, I will replace it when I feel like spending a couple of bucks, though. This motor is in such good shape overall, that I would like to just go through it, one thing at a time. It is a low time motor and has been very reliable up to this point so I don't mind working my way towards all new parts to maintain dependability.

PS: Just spend a little time reading the manual. Actually the carb adjustment procedure doesn't look too bad. The carbs look to be nearly identical to the ones on my 58 thirty fives and 67/69 thirty threes, with the exception of the linkages and the high speed jets (fixed) on this motor. The book runs you through a procedure to arrive at a certain setting for the #2 & #3 carbs and then one for the #1 carb. Not too terrible but if anyone is aware of any common mistakes that noobs make, your words of wisdom would be appreciated.