Fuel system pressure test, old Johnson.

[Franki]

Hello people..<br /><br />I have strange fuel issues which I have recently detailed in this list on another post.. no one responded so I thought I'd try something else..<br /><br />This morning I hooked up the fuel tank, and started pumping the primer till it got hard, then I pushed hard.. <br /><br />the plunger slowly went down.. then after a few hard squeezes, fuel started running out of both the overflows on each carb...<br /><br />(two small holes between the throats of each carb..)<br /><br />my question is this..<br /><br />How hard is to hard when squeezing the primer.. ?? I know that with anough pressure I could force fuel past the needles.. but how much would be acceptable? <br /><br />I had the floats out and all was clean and in good nick.. so I'm alittle lost here.. it has to be the floats and needle/seat.. but they all look fine..<br /><br />I'd love to hear some suggestions here...<br /><br />rgds<br /><br />Frank

 

[petryshyn]

Re: Fuel system pressure test, old Johnson.

Franki<br />If you are truely interested in what is too hard, tee in a fuel pressure gauge between the primer bulb and the fuel pump. See what it feels like to squeeze 2-5 psi on the gauge. Any more than that is too much on your old Johnson

 

[Franki]

Re: Fuel system pressure test, old Johnson.

Fair enough,, I will try and do that...<br /><br />I have just read many times that the bulb should stay hard and not compress, and mine does.. although slowly and requires some force to do..<br /><br />Here is a pic of the carb, I have roughly marked where the fuel was coming out.<br />

<br /><br />I knew the fuel pump shouldn't be putting out more then 5.. but didn't know how much resistance the needle and seat would give.. so I did the primer test to see if it was the fuel pump having too much pressure or the needles/seats not sealing properly..<br /><br />It would seem to be the latter I think. (but I don't know how hard the primer is pushed translates to pressure..)<br /><br />Since it happened at the same time on both carbs.. and both chambers/floats/needles seemed in good nick and clean.. I am thinking that maybe it is not supposed to handle that much pressure and maybe my fuel pump is pushing too hard..<br /><br />anyway.. I guess I am going to buy a fuel pressure tester.. thats more money :-( (just bought a compression tester last week.<br /><br />I have a spare fuel pump here, so I might change that over as well.<br /><br />If Schematic or anyone has any other tests I might try in order to narrow down the search criteria,,, I'd really love to hear them.. this is the last issue I have to deal with.. after this I can take this puppy out on the water and try it.. (I have not had this motor on a boat yet..) <br /><br />regards<br /><br />Franki

 

[petryshyn]

Re: Fuel system pressure test, old Johnson.

I think what you're seeing is normal. I'm sure you can squeeze way more than 5 psi. The ball is never going to be "rock hard" (unless you leave the vent closed on a hot day)It will always have "some" give.

 

[Franki]

Re: Fuel system pressure test, old Johnson.

Cool, <br /><br />Thankyou Mr Schematic..<br /><br />I think that means I have a bad fuel pump because occasionally I get fuel comming from those holes when the motor is running.. and it keeps comming till I disconnect the fuel line for 10 seconds.. <br /><br />after I put it back on, it seems fine..<br /><br />since there are two carbs, and both are doing it.. and there is only one fuel pump, statistics would tend to indicate that the problem is most likely to be the fuel pump..<br /><br />guess the only way to tell is to swap it for my spare and see if it still does it.. or buy a fuel pressure guage and check the pressure..<br /><br />how can a fuel pump give too much pressure though? I figured if it was failing the pressure would drop, not rise..<br /><br />rgds<br /><br />Frank

 

[petryshyn]

Re: Fuel system pressure test, old Johnson.

Unlikely the fuel pump. Did you check the float levels carefully? Better yet, did you adjust them? Is the engine "level" when this happens? Have you changed the needles and seats?

 

[Franki]

Re: Fuel system pressure test, old Johnson.

Hi again Mr Schematic..<br /><br />Thanks for helping me with this..<br /><br />I pulled both chambers out.. checked for gunk first.. both where perfectly clean..<br /><br />then tested floats.. soaked them in a tub of fuel.. no leaks, no wear or bends in the needle tab..<br /><br />then I checked the needle, they have a rubber tip cover on them and there was a really tiny line on one of them where it was meeting the seat.. the other seemed perfect.. <br /><br />the seats where likewise spotless and no sign of wear..<br /><br />I figured that it was unlikely that the same problem would happen in both carbs unless it related to dirty fuel or congealed fuel in the bowls.. once i checked that that wasn't the case, I started looking elsewhere...<br /><br />So I was right? an outboard fuel pump wouldn't increase in pressure if it was failing???<br /><br />regards<br /><br />frank

 

[petryshyn]

Re: Fuel system pressure test, old Johnson.

Not that I've ever seen. Do the pressure test and see what you have. You wanted to get the feel for what you could squeeze anyway. Get a fuel pressure/vacuum gauge. $10-$15 Good investment!!

 

[Franki]

Re: Fuel system pressure test, old Johnson.

Ok, <br /><br />Will do.. I'll post my findings...<br /><br />I have worked though the night.. (and posted here) and now its 9 in the morning..) so I need sleep.. so I guess this hasta wait till I wake up..<br /><br />Thanks again for your assistance..<br /><br />much appreciated.<br /><br />rgds<br /><br />Franki