1954 10hp Johnson Fuel Pump Conversion

[MNmarty]

1954 Johnson 10hp fuel pump conversion
Yesterday at 10:31pm Quote
I'm stumped. I converted this Johnson for an old friend and shipped it to AZ from MN. I used the technique shown in http://outboard-boat-motor-repair.com/Johnson/Pressureized Fuel Tanks.htm .
I've done this before on my 7.5HP and 5.5hp. I used the Mikuni pump as shown in the article.
The problem is the motor runs out of gas. It does not appear that the pump is working correctly. The lines from the tank have been checked. The vacuum line from the intake manifold cover is secure and tight. He even opened up my conversion and made sure the plug is secure in the crankcase hole.
He started the motor and disconnected the hose to the vacuum port on the pump.He really couldn't feel any vacuum. Just positive pressure. Neither of us know how it's supposed to feel.
Essentially he has redone the conversion and re-checked everything I had done.
The question is whether the brand new pump is somehow defective or are you supposed to feel more of the vacuum pulsations at the end of the line that connects to the vacuum port on the pump. As you can imagine my "gift" has turned into a mess. When I tested the motor beforehand it ran dry, but I tightened my line from the intake manifold and it seemed to work great after that.
Is there a way to check if the pump is working correctly? or if the conversion is done correctly?
Thanks for any help.
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[bktheking]

Re: 1954 10hp Johnson Fuel Pump Conversion

This sounds like the 5.5 i'm working on. Runs great for a minute or 2 then dies. I'm running the pressure tank instead of a pump. I know my tank works as I can run it on my 7.5 without issue. I posted the same like question on AOMCI and F_R replied suggesting that the sintered filter that sits in the glass at the bottom of the carb might be causing the issue. They will start and run fine after priming cause the pressure will force gas into the carb but they lose fuel after a bit due to filter restriction, just a thought.

 

[F_R]

Re: 1954 10hp Johnson Fuel Pump Conversion

A very real possibility. As a temporary test, remove the filter and see if it then keeps running.

 

[MNmarty]

Re: 1954 10hp Johnson Fuel Pump Conversion

I'll have him try it but I doubt that's the problem since I rebuilt and cleaned the carb before sending it. Ya never know, though.

 

[bktheking]

Re: 1954 10hp Johnson Fuel Pump Conversion

Yup, did the same last night, rebuilt the carb and it runs great, didn't touch the filter.

 

[MNmarty]

Re: 1954 10hp Johnson Fuel Pump Conversion

Well, I've finally figured out a problem that has plagued many others before me.
I went to TwinCityoutboard in Shakopee, MN. They have thousands of outboards in the back. I figured they would know what to do.
We talked about the problem. He felt it had to be the Mikuni pump, but admitted they were very reliable. He also felt that the placement of the pump directly on the cylinder bypass cover would be more reliable. He wasn't too excited about the conversion process outlined above. He searched and searched for a newer cover that the pump could mount directly to. No success. So he gave me a replacement cover and a barb fitting and told me to tap a hole and install it. He didn't want to sell me a brand new pump, which I thought was pretty honest of him, and told me the Mikuni should work when connected to the cylinder in this fashion.
I was about to leave when his partner said, "Those Mikuni's can be tricky. The pulse line to the pump can't be too long or too short. If it is, it won't work properly."
I called my friend in AZ and told him what happened. After hearing this he moved the pump from the convenient placement on the side of the motor to the front under the carb. This shortened the pulse line considerably.
You know what happens next? It works flawlessly! Maybe that's why it works on smaller engine blocks like the 5.5 and 7.5hp. Maybe the lines are just a touch shorter.
So I think this may be a variable most haven't thought about. The above conversion does work. It's just that the pump mounted way back, on the cylinder bypass cover, has a much shorter pulse line to the pump.
Hope this helps the next guy.
Thanks for your help.

 

[Spider john]

Re: 1954 10hp Johnson Fuel Pump Conversion

Hate to drag this up from so long ago, but as I am in the process of doing the same conversion, I thought I would ask a question about this.

These motors have a check valve to stop the vacuum portion of the cycle from affecting the tank. The check valve keeps the tank pressurized. I would think that this is what keeps you from feeling the vacuum pulses.

I haven't removed the check valve, but I am tempted. Has anyone done this? What were the results?

 

[levi_tsk]

Re: 1954 10hp Johnson Fuel Pump Conversion

you gotta pull the check valve and then plug one of the holes that are under the check valves with a vacuum cap and put it back together and yes if you dont plug it properly you get a weak pulse signal that would cause the above problem