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1989 Johnson 40hp W.O.T. issues

M

mthompson10744

New member
Hello to all , I'm currently having an issue with my 1989 Johnson 40hp . Boat struggles to start occasionally but my big issue is that I can't hold WOT for more than 30-45 seconds. Coming out of the no wake around 1k-2k rpm it is fine but as soon as I push past 4k rpm the engine will run strong for that 30-45 seconds and then spit and sputter sometimes it will die if I don't back out of the throttle. Sometimes the engine will just "pulse" and "lag" around 2k rpm if I stay in the throttle and it doesn't die.

Just bought the boat in June and I've had the problem since first time out on the water. So far I changed fuel tank(brand new 12gal), new fuel filter and primer bulb, rebuilt carbs(floats are adjusted properly) and I replaced the plugs. I inspected reed valves while carbs were off they were fine. I just ordered a new ignition coil, plug wires and new plugs.

I'm wondering if something inside the VRO pump could be causing this ? The engine was converted to premix long before I got it. The oil tank is gone and everything appears to be sealed up air tight I don't believe I'm sucking air . I plan on replacing all the fuel lines on the carb/vro as they are still old. I'm not sure how old the VRO pump is so I'm curious as to if it could be playing a factor ? I plan on also doing a compression test this weekend .

Any else wanna throughout suggestions? I greatly appreciate it!

Thank you
 
I have a few thoughts on this. You seem to be heading in the right direction on what you are doing. Have you replaced the water pump and thermostat?
As you, I would also suspect the fuel pump. I assume that it idles fine and up to 2k is fine but when throttled up it takes a nose dive after 30 to 45 seconds. Possible the fuel pump is not supplying what the carbs demand. The motor still has the vro pump installed and used as a fuel pump only. Not the proper way to convert one of these to premix.
There are a lot of vids on youtube about this. Some are what you have , and some done right. One I seen about a week ago was very good, everything done the right way. Check it out. Decide what you want to do from there.
When you do the compression test. Please post the numbers. Not just above xxx or yyy but the actual numbers per cylinder.
A complete model number is very important also. Please post that if possible.
Good luck with your project.
 
I have not checked thermostat or water pump. I'm curious how they would play a roll in my WOT issue? The impeller was changed before I bought it . Engine pees warm but not hot water.

I was thinking about switching the fuel pump to Johnson PN: 0438559 . Its a non vro style with the in/out and pulse line which is what I need . Seems like a pretty easy switch . Local marina has the part , might swap it out tonight with new fuel lines and make a test run tomorrow.

I will try and get model number and compression numbers tonight as well

Thanks again !
 
A few things I would check. First, did you physically clean the jets in the very bottom of your carb? Because it kinda sounds like your high speed jets may be clogged.

Second, Is the link and synch correct? You can easily find instructions for your motor in this forum.

Third, are your carb bowls warped? If they are plastic, they could be. You can put sandpaper on glass and rub the bowls in a figure eight to see if they are even.

Oh, did you try pumping the fuel bulb when it bogged down?
 
Last edited:
riopga said:
A few things I would check. First, did you physically clean the jets in the very bottom of your carb? Because it kinda sounds like your high speed jets may be clogged.

Second, Is the link and synch correct? You can easily find instructions for your motor in this forum.

Third, are your carb bowls warped? If they are plastic, they could be. You can put sandpaper on glass and rub the bowls in a figure eight to see if they are even.

Oh, did you try pumping the fuel bulb when it bogged down?
Click to expand...



-I completely tore carbs down and sprayed all the jets & passages with with carb cleaner and blew them with 20psi air pressure.

Are you referring to the throttle linkage ? It looked good but if you are referring to something else I will look at it too.
the carb bowls are aluminum .

I believe I did try and squeeze the fuel bulb and nothing changed but I can't remember 100% . I will try that this weekend when we have it out. I'm going with my gut feeling that maybe something in the VRO is just old and not functioning as it should but I'm not sure. It feels like a fuel issue to me.

If I squeeze the bulb when it studders and it does nothing where should I look next ?

Thanks again !
 
aquarius23 said:
I have a few thoughts on this. You seem to be heading in the right direction on what you are doing. Have you replaced the water pump and thermostat?
As you, I would also suspect the fuel pump. I assume that it idles fine and up to 2k is fine but when throttled up it takes a nose dive after 30 to 45 seconds. Possible the fuel pump is not supplying what the carbs demand. The motor still has the vro pump installed and used as a fuel pump only. Not the proper way to convert one of these to premix.
There are a lot of vids on youtube about this. Some are what you have , and some done right. One I seen about a week ago was very good, everything done the right way. Check it out. Decide what you want to do from there.
When you do the compression test. Please post the numbers. Not just above xxx or yyy but the actual numbers per cylinder.
A complete model number is very important also. Please post that if possible.
Good luck with your project.
Click to expand...


-I have not checked thermostat or water pump. I'm curious how they would play a roll in my WOT issue? The impeller was changed before I bought it . Engine pees warm but not hot water.

I was thinking about switching the fuel pump to Johnson PN: 0438559 . Its a non vro style with the in/out and pulse line which is what I need . Seems like a pretty easy switch . Local marina has the part , might swap it out tonight with new fuel lines and make a test run tomorrow.

I will try and get model number and compression numbers tonight as well

Thanks again !
 
The reason I asked about the t-stat and water pump was just to eliminate any issue with overheating and seizure. Sounds like you have that under control.
When I done this conversion a few years back it was on a early 90's evinrude. I do not remember the part number of the fuel pump I used. It was for the same year and horsepower as the motor I was converting , but the the pump was for a rope start motor non vro. It bolted to the motor right behind the starter. You should see 2 threaded holes with a bolt between them. That bolt should have a plastic washer on it. That is your pulse port for the pump. You will not use that bolt or washer. The 2 threaded holes is where the pump bolts up. Very easy to mount and no pulse line to run just fuel in and fuel out. Behind the starter down low on the motor you will find the pulse line that goes to your vro pump. That line hooks up to a pulse limiter. That was no longer needed so I just removed the limiter and screwed a plug into the hole.
If you decide to make this conversion be very careful with the plastic fuel manifold. Very easy to break and about $70 to replace
 
aquarius23 said:
The reason I asked about the t-stat and water pump was just to eliminate any issue with overheating and seizure. Sounds like you have that under control.
When I done this conversion a few years back it was on a early 90's evinrude. I do not remember the part number of the fuel pump I used. It was for the same year and horsepower as the motor I was converting , but the the pump was for a rope start motor non vro. It bolted to the motor right behind the starter. You should see 2 threaded holes with a bolt between them. That bolt should have a plastic washer on it. That is your pulse port for the pump. You will not use that bolt or washer. The 2 threaded holes is where the pump bolts up. Very easy to mount and no pulse line to run just fuel in and fuel out. Behind the starter down low on the motor you will find the pulse line that goes to your vro pump. That line hooks up to a pulse limiter. That was no longer needed so I just removed the limiter and screwed a plug into the hole.
If you decide to make this conversion be very careful with the plastic fuel manifold. Very easy to break and about $70 to replace
Click to expand...


Was able to swap out the fuel pump to the non VRO style , plugged the old pulse line and mounted new fuel pump to the block as you stated how to do it in previous reply. After doing that and new ignition coil, plugs and wires the issue is completely resolved. We had the boat out Monday and I was able to push past 5k rpm for as long as needed. Felt good finally being able to have a nice cruising breeze. Thanks again to everyone who gave direction as to where I should look !
 
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