1979 Johnson 140 that wont rev up and surges

[Hacker]

I want to start off by saying that I just joined but have been reading all your great information for a few months. Thanks! As well, this is long winded, but I want to get across the details of the problem and all my work.

I recently picked up a family boat with a 1979 140HP Johnson that had been sitting for years. I had not read all the great "waking a sleeping..." article and ended up paying for it. I did replace all the fuel lines/bulb, tanks and plugs just to see if the motor ran. Once it did, I started on more boat projects. Needless to say, I found the boat had a lot of the problems other posters have mentioned (stalling at wot, poor idle, not reaching full power,...). After all this, I found that one cylinder was dead. It had eaten a ring, so next came the complete rebuild (bore, re-ring, carb rebuild, seals, gaskets, fuel filter rebuild and new fuel lines to the carbs).
I took it out for the break in period and everything was perfect! Well at least for the first ~6 hours on the motor. I started having surging problems and with each trip it got worst. When going past 1/2 throttle, the motor would jump upt to wot and then surge back and forth. I found that it worked when pumping the bulb, so that led me to finding the fuel line to the lower carb had become kinked and likely was restricting flow. I tore apart the fuel delivery system and fixed the problem (along with a double check on the carbs and filter since they were off).
I took the boat out again and although the problem was not as bad, it still exhibited the same issue (the surging was now ~1/2-3/4 throttle as compared to the previous where the low was just above idle). it would rev out for the first minute or so and then cut back to ~3/4 throttle before surging down)
I brought the motor back and went through all the following tests:
- compression OK (125, 125, 125, 119)
- pulled plug on each at idle and noticed the drop in RPMs
- checked the timing and each were as expected (#1 - 4deg btdc @ idle)
- tank vents open
- carb throat flaps are in sync with each other at idle and up to wot

So now I am past my ability to find the problem. I am in search of a spark gap tester to try and rule that out. I have noticed all spark plugs are a little dirty, but dry except for #1 which is a little wet. As well, I have fuel leaking out the front of the carbs. I don't like this, but assume its coming from the float bowls when the tilt is up.
If you can offer suggestions, I would appreciate it. I want to find out if this is electrical or fuel related and how I can find the source of the problem.
Thanks in advance!

 

[tashasdaddy]

Re: 1979 Johnson 140 that wont rev up and surges

does it still correct itself if you pump the bulb? if so i would look at fuel pump.

 

[Hacker]

Re: 1979 Johnson 140 that wont rev up and surges

I knew that question was next since I was unable to check it last trip (I had no passenger help). I will check this today.
One other thing is that I tightened all grounds as well as adjusting the butterfly valves a bit in case they were contributing. I need to check if these made a difference as today as well.
I know this sounds like the fuel pump, but I can't see why it would be the culprit due to a clean out and a rebuild.
I don't have a way to test the fuel pressure but thought there could be a problem with the pressure from the block... could it get junked up?

 

[Hacker]

Re: 1979 Johnson 140 that wont rev up and surges

I knew that question was next since I was unable to check it last trip (I had no passenger help). I will check this today.
One other thing is that I tightened all grounds as well as adjusting the butterfly valves a bit in case they were contributing. I need to check if these made a difference as today as well.
I know this sounds like the fuel pump, but I can't see why it would be the culprit due to a clean out and a rebuild.
I don't have a way to test the fuel pressure but thought there could be a problem with the pressure from the block... could it get junked up?

 

[ezeke]

Re: 1979 Johnson 140 that wont rev up and surges

It is important that the function of the fuel pump is to fill the float bowls and has nothing whatever to do with moving fuel beyond the float bowl into the engine with choked carburetors. Generally, the symptom described as surging is caused by air leaks.

It is possible that the air could be coming from the fuel pump gasket.

The fuel running from the carburetors is usually caused by malfunctioning float valves although engines drain better when stored in the running position.

If you can get fuel into the carburetor throats by squeezing the primer bulb, your float valves are not working properly.

 

[Hacker]

Re: 1979 Johnson 140 that wont rev up and surges

I agree that it sounds like an air leak issue, it's just that I can't find it. I will see how goes today and if problems still exist, I'll work on the pump. I need to check the test where I blow from input to output and from output to input. I did this in the past and air went through both... I later found the center spring had tipped to the side rather than be verticle. I thought that was odd as it must have been during the process of aligning the diaphram before tightening the screws.

Thanks again.

 

[ezeke]

Re: 1979 Johnson 140 that wont rev up and surges

the fuel pump gasket is between the fuel pump and the motor. Unless the diaphram is ruptured, nothing passes through the pump that would cause surging, but a bad gasket behind the pump will allow air to leak into the cyliinder.

 

[Hacker]

Re: 1979 Johnson 140 that wont rev up and surges

So I took the boat out today for some testing it was fine in the morning. I idled the motor for about 5 minutes and then the boat ran great. After ~10min, I pulled back to idle and then back up to wot again to see if this would trigger the problem. It worked great ~10 minutes so I stopped testing (I mostly ran at 3/4 throttle due to still being under the 10 hour break in period).
Now came the bad part. Since it was working fine, I began fishing off the trolling motor for the next 2-3 hours while the motor was off. I then headed back and after a couple minutes I felt the noticeable change in RPMs and then the surging started again. I cut back to idle and then back to wot... it ran for another couple minutes and then the surging but this time more pronounced. I pumped the bulb and there was no change in RPMs.
I did this a few more times and then headed back to the dock. When idling in the 'no wake' zone, I could still feel the surging (although very softly).

I'm concerned the boat ran great until it got somewhat hot and then started to fail. The morning run was in the mid 70s and the afternoon was the mid 80s... al previous surging was on 100+ days (no cool days until this week).
I read some issues about coils or powerpacks faiding at higher temps. Could I test for this somehow? Or do you think I should still be looking for a fuel problem? Thanks.

 

[emdsapmgr]

Re: 1979 Johnson 140 that wont rev up and surges

Put an inductive timing light on each plug wire next time it begins surging. You are looking for strong, constant, flashes from the light on each plugwire. If you get weak or intermittent flashes, then it's an ignition problem. Electrical components do tend to fail when the engine warmed up to normal operating temps. A weak pump can cause surging. Usually this is most noticeable at high speeds. If the engine consumes more fuel than the pump can deliver, it will surge up and down, based on the amount of fuel in the carb bowl. Your squeezing the fuel hose primer bulb is an excellent test of the pump. If it runs well while constantly pumping the bulb, you are helping the pump keep fuel in the bowls.

 

[Hacker]

Re: 1979 Johnson 140 that wont rev up and surges

Is the inductive timing light something that can be connected and left on while running? Or is this a little handheld light that you put next to the wire?

I have an inline spark/ignition tester with the light (versus the adjustable gap type that no one had nearby). can i just connect these and leave them on while running? Or do the inline ones take away from the spark (powering the light)?

Thanks.

 

[ezeke]

Re: 1979 Johnson 140 that wont rev up and surges

The inductive type clamps around the wire and can be left in place as you run the boat so that you can determine where the breakdown is taking place.

 

[Hacker]

Re: 1979 Johnson 140 that wont rev up and surges

So I did a couple more tests to validate the situation but have not had the chance to take it out on the water (likely this Sunday).
I used an inline spark tester and set the gap at 7/16 on each cylinder and saw a spark jumping on all wires. I also did the wot timing check with the motor off and the advance up against the bumper and saw ~23 degrees btdc vs 24. Should that have any impact on performance?

Also, with the spark jumping the gap at idle, could a power pack fade at temperature still be enough to effect it?

Thanks.

 

[ezeke]

Re: 1979 Johnson 140 that wont rev up and surges

More likely that the ignition coils fail under load and heat. Look them over carefully for cracks, melting, discoloration or corrosion. If they are bad, they can kill a powerpack. Also, don't use automobile spark plug wires, you need solid core.

 

[Hacker]

Re: 1979 Johnson 140 that wont rev up and surges

Well I finally got the boat out again today for testing. Again I could not isolate anything. I brought a spark tester out on the water and couldsee the light, so it was useless. I then connected up the timing light and at least could test one wire at a time. When the surging and rpm drop started, there was nothing noticeable on the timing light shuch as gaps in spark. As well, I could not tell at wot since the like just seemed to be on continuously.
I then went back to the bulb test and that did nothing either.
Although I have rebuilt the fuel pump, would there be any reason to buy a new one?
Also, I ran the the boat for a good 5-7 miles at 3/4-wot this time when I first got on the water and there was not a hiccup at all... that should be plenty of time for the motor to heat up. I then shut it down for ~45 minutes and then started up again... this time it started failing after ~1 minute at wot. This is the same phenonmenon I saw last time out and assumed it was heat related. Any thoughts?

 

[Hacker]

Re: 1979 Johnson 140 that wont rev up and surges

Now for the latest... in my previous carb rebuild, I did not soak the carbs in cleaner since it all looked quite clean inside... so I thought this needs to be done just for my own sanity.
I tore them down today for a soak and (after making the jet tool) I went to take out the jets... I found one of the main jets was loose in the screw hole area (likely letting too much fuel in). That was the one wet spark plus as well. I was going to remove the jets in the past but had only a small screw driver and started but thought the jets would break... I guess I had loosened one just enough and did not know it. That would explain the two days of solid running before the surging began. So I just completed the complete soak and rebuilt... I hope to test tomorrow.
My only concern is to why the boat works fine the first run and then starts acting up. This still has me questioning the problems, but I hope to have a working boat finally... my fingers are crossed!

 

[emdsapmgr]

Re: 1979 Johnson 140 that wont rev up and surges

When you get all the jets out, spray a can of aerosol carb cleaner through each carb. All passages. Compare the stream of cleaner on each passage, each carb. The fuel circuits can plug up or restrict and you can't tell, except by how well the cleaner sprays through each passage. There is a special tool for taking out the jets: 317002, avail at your local Bombardier dealer.

 

[wavrider]

Re: 1979 Johnson 140 that wont rev up and surges

I had a fuel tank that had a bad pick up hose in it.

A little over 1/4 of the way down the hose, inside the tank was a small hole, once the level of the gas in the fuel tank got below this hole my engine started showing the same sysptoms as yours.

Try a different fuel tank just to eliminate this.

Reading your posts it seems lke it runs pretty good for a while when you first start the day on the water, then after some fuel consumption it stats acting up.

The timing light being constantly on is a good sign.

Whatever the problem is when you find it it will be simple, something as small as a piece of rubber hose blocking the fuel line.

This mystery problems can eat up some time troubleshooting. Good luck and let us kow what you discover.