how many psi for a JOHNSON QD-12, 10HP?

[adrn13]

I have a JOHNSON QD-12, 10HP witch im suppose to use with a pressure gas tank I was wondering if anyone know how many psi Im suppose to to have in the tank for it to work? thanks

 

[Daviet]

Re: how many psi for a JOHNSON QD-12, 10HP?

The engine provides the pressure. If the hoses and tank are in good shape and the engine is running properly, no need to worry about pressure.

 

[bktheking]

Re: how many psi for a JOHNSON QD-12, 10HP?

Cool motor, just got one myself. Like Daviet said, the motor provides the pressure to the pressure tank. However I did discover something interesting with mine when I pulled the carb off. The spring which holds the bypass valves in place was bent on one side, there is normally a slight bend in both directions but the one side on mine was bent too much, to the point that the valve had come off of the spring. So with no REAL experience with the system I mistakenly just stuck the bypass valve back onto the spring without fixing the bent spring. The motor ran but would die after a minute and the tank no longer had pressure.

I did some research and found out that the if the spring was bent like it was it was caused by a backfire (there is an OMC bulletin on this system and reference to bent springs, not exactly a spring found at your local hardware store.) Logic told me that the valve was closed and is now open so the spring needed to be bent back so I re and re'd the carb and bent the spring back and all started working again. Look at the top valve, it is open an 1/8 of an inch.


Now i'm not saying that this "is" the issue, if you have known good pressure tank (I have 3 pressure tank motors so I know mine was good) and all the lines are good this is the first place i'd look for a "pressure issue". It's a very simple design but if the valves aren't seating/sealing properly you won't get pressure.

 

[bktheking]

Re: how many psi for a JOHNSON QD-12, 10HP?

Just in case you have to remove the carb, it is not easy to remove, the intake and the carb are one piece.

You have to remove the float bowl with the carb on the motor, this gains access to the screw in behind, the rest are easy. Be VERY careful with the copper lines, after I did all this work I had a leak at the sediment bowl, I had to cut the copper and put in a new 3/16th brass compression sleave, also not easy to find.

 

[adrn13]

Re: how many psi for a JOHNSON QD-12, 10HP?

One of the reasons why I was asking is because my pressure tank is getting rebuilt and it is suppose to take up to two week because he has to order some parts to get it done and the mechanic let me barrow a electric fuel pump of 3.5 psi and told me I could use it until he finish with my tank be Im no sure if is to much pressure for my motor or if 3.5 is fine.

 

[bktheking]

Re: how many psi for a JOHNSON QD-12, 10HP?

Should be fine (i've read 5 psi in the past), don't know if I like the electric fuel pump idea but I'm not opening another can of worms, your choice

 

[adrn13]

Re: how many psi for a JOHNSON QD-12, 10HP?

haha thank captain (bktheking).