Logo
FULL SITE MENU

1988 Johnson 150 GT Vro to Mech. fuel pump change over question

O

oran

New member
Hello all, I am changing the VRO system over to mech. diaphragm fuel pumps on my 1988 150Gt Johnson, and have a few question.
Question 1- Can I use the same vacuum line and just put a tee in to run the second fuel pump? Or do I need to use a second vacuum line from the other vacuum port? If I do have to use a second line do I have to use a check valve in the line?
Question 2- When plumbing the the fuel line do I put the pumps in series and have the outlet of one pump feed the inlet of the next pump and then out the second pump to the carbs? Or can I run one pump to feed one carb and the other pump to feed two carbs?
Thanks in advance for your help.
 
poop said:
what kind of mechanical fuel pump are you talking about ?
Click to expand...

I had purchased fuel pump off ebay that were from a 1979 175 hp. Johnson. They are the old diaphragm type fuel pump that have a a fuel inlet,outlet and a vacuum port brass fitting on the bottom. After recieving these pumps I went ahead and rebuilt them with all new gaskets and diaphragms.
 
The 2 pumps are put in series with the fuel going thru both pumps.-----------Use the pulse ports from the motor ( one to each pump ) and it will work just fine.----------A V-6 uses 3/8" fuel line from tank to the motor.
 
It is not a " vacuum line " it is a pulsing port !!!----Absolutely no check valve as pumps operate on a positive / negative pulse.---------------------You run one pulse line to one pump and the other to the second pump.---No need to make this complicated at all.-----With a check valve in the line the pump would not work.
 
It is a " pulse limiter " to protect the VRO pump from backfire in the motor.-------------Not installed for the earlier pumps at all !--The two pumps run from different cylinders.Each cylinder has its own crankcase.
 
Since they were not installed on earlier models,does that mean I should to remove the existing one, or just leave it?
 
not sure it's supposed to be series (fuel tank)------(pump1)------(pump2)------(carbs)


Aren't they supposed to be in parallel? (fuel tank)-------\----(pump1)-------/--------(carbs)
.......................ignore dots. formatting....................... \---(pump2)------/

I'm not certain either, but parallel is what I seem to remember.
 
Last edited:
See post # 4 for the correct path !----------------Discharge from pump 1 to intake of pump 2 then out to carburetors.------Check that by going to the parts pages if you must.
 
Thanks again racerone. I finished up the change over this afternoon, and fired it up in the yard. I had to fabricate a mounting and then plumbing. I wanted to test run it,but the wife and daughter didnt want to go for a boat ride. So its looks like next weekend on the test run. I did fire it up in yard and ran fine @ idle,but I know there is a difference from idle and full load. Thanks again for all yall's help.
 
Back
Top