73 Johnson 65HP 3500 max RPM

I have a 73 johnson 65hp that won't go over 3500 RPM. The stator tests good and the carbs just had a fresh rebuild. I just replaced the rectifier due to the insulation on one of the wires was getting pretty weathered. I know for sure it isn't the Tach or the Prop. I used to run 5K on the RPM easily. The motor will hit 4K for a moment and then it kicks back down to 3500. I tried a lower pitch prop also and it still only hit 3500. The primer bulb stays hard and I have an electric boost pump that doesn't change anything. I am thinking that I have a power pack issue but I am not totally sure how to ops check it without buying a bunch of other expensive tools that I won't use often enough. I have a factory service manual and it really doesn't say much on testing a power pack with a conventional volt meter. I am just debating whether I want to drop the hundred bucks for a new pack or not. The motor starts great and will run all day at 3500. It is sluggish at getting to plane though. The hull is not saturated either. Just finished new transom and stringer job (will never do that again). Any ideas would be greatly appreciated.

Re: 73 Johnson 65HP 3500 max RPM

Sounds like a coil breaking down when it gets hot.Take a buddy and a good old fashioned timing light and see if you get consistent spark when running. Careful to not throw him out of the boat by accident (or on purpose) as you will be running without the cover on. If you are sure that it is not a spark problem I would do a link n sync on the carbs so I know that the butterflies are working at the proper time.

Re: 73 Johnson 65HP 3500 max RPM

To add where fireman57 left off. Take your throttle control and check to make sure you actually are getting wot! Post back results.

Re: 73 Johnson 65HP 3500 max RPM

The carbs have been synch'd and when the control is at WOT the butterflies are as far open as they can get. The only thing that is really annoying me is when the boat is in neutral I can rev the motor up just fine at the carbs with no load on the motor. Will definately try the timing light idea. Just not overly thrilled about the idea of the wife driving. I have checked the spark and I have stopped and pulled the plugs in the middle of the lake and none were getting fouled. I pulled the carbs again after two trips out and tore them down again and they were as clean as can be. Even pulled the jets out and verified they were clean. I run a couple portable tanks so I know the gas isn't bad and I run non-ethanol. Hopefully it is just a timing issue. The wife is getting grumpy with the whole rebuild cost.

Re: 73 Johnson 65HP 3500 max RPM

Check your throttle stop on the engine.They may not have it out as far as you need to go. Without it running have your wife push the throttle all the way forward, you will see the timer base turn and an arm will come to hit a rubber stopper. You may just have to adjust this out. You can do this in your driveway so you don't have to worry about yelling at your helper.

Re: 73 Johnson 65HP 3500 max RPM

I had same prob on my 65hp Johnson. HEADGASKET:?(

Re: 73 Johnson 65HP 3500 max RPM

you said that butterflies are as far as they will go .you dont want them past level

Re: 73 Johnson 65HP 3500 max RPM

Sidserv said:

. The wife is getting grumpy with the whole rebuild cost.

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I am having the same problem Any help or opinions are greatly appreciated

Re: 73 Johnson 65HP 3500 max RPM

Well I took it out sure enough it acted up again. The top cylinder died. I replaced the coil with a known good one and it cut out after 10 minutes. I have replaced the head gasket as well as the the thermostat. I don't have a problem with compression. Running 135 ish in all three cylinders. The butterflies are flat level when wide open. I do know the coils are origional as well as the power pack, stator, and trigger. Only reason I replaced the head gasket is a buddy of mine decided to put his idiot strength into tightening a sparkplug. So I bored the plug hole and a solid insert repair later the head was fixed. Also added a pee hole on the motor during the process. Never liked the exhaust spritzer for monitoring a functioning water pump. I can do mechanical. Just not worth a damn at electrical. So I am down to replacing the coils and powerpack. Going to pull the flywheel next weekend and look at the stator and trigger also. Motor starts right up so I am really doubting the stator and trigger are bad.

Re: 73 Johnson 65HP 3500 max RPM

I had the exact same problem you are having and replaced all the same parts with you and couldn't get the problem sorted out. My carbs had just been rebuilt as well, and I finally decided to take them apart because there was nothing left to replace, and wouldn't you know the middle carb float screw had loosened up and caused the whole problem. Maybe this isn't the answer for you, but I would at least take a look. If it is at least you'll now have most of the major ignition pieces replaced and you shouldn't have to worry about them for awhile!

Re: 73 Johnson 65HP 3500 max RPM

I will probably tear them down again just for the fun of it. I have to wait on the parts to come in anyway. Not in a huge rush anyways. Nothing more fun than sticking a yamaha 25hp on a 12 foot aluminum. Little boat will run 35 on the lake. Little scarey on turns though.

Re: 73 Johnson 65HP 3500 max RPM

If you changed the ignition coil and got the same result, my guess is that one of the three circuits in the powerpack is breaking up, or you have have a bad sensor coil in the timer base.

Do you have an OMC manual for your motor?

Re: 73 Johnson 65HP 3500 max RPM

I have the OMC manual. I have been leaning towards the powerpack. Unfortunately I haven't had a chance to work on it.

Re: 73 Johnson 65HP 3500 max RPM

Ok I have replaced the stator due to a crack in one of the coil packs. Well that didn't cure the problem. Powerpack is next. Have another one so trying that tomorrow