Johnson 70 Fuel issues

[strickland]

i have a 2000 model 70 johnson outboard and a little bit stuck as its starves for fuel
ive rule ruled out electrical and this is where im stuck
3 carbys prime easy motor starts easy and runs really good for about 20mins full throttle and then bogs down
ive cleaned the and seviced each carby with same result
it seems the bottom carby was staving for fuel so i swapped carbys around and same result with bottom starving of fuel
10 15 mins later its right to go but keeps cutting out
other 2 carbys dont dry up so ive ruled out the carbys
changed the valve from the crank case that goes to the pump also with the same results also changed the pump aswell with same results
not sure why the bottom carby is running dry could it be a vacuum issue
not sure just stuck

[boats.net]

Have you tried pumping the fuel primer bulb to try and keep it running, would indicate fuel problem in boat. Is fuel primer sucking flat, if so have a fuel restriction in boat. Try bumping choke when it boggs to see if rpm's pick up, would indicate carb problem. If boat has a built in gas tank try running on a new portable gas tank and new fuel hose to eliminate boat fuel problems.

[strickland]

Hi thanks for the reply
what I don’t understand is that the other two carbs don’t run dry at all it seems to be only the bottom one which is connected to crank case I’ve changed all fuel lines as well but same results
bulb does run soft but keep priming it doesn’t seem to make a difference straight away it takes a while
could this be a vacuum issue why the bottom carby runs dry
I know the pumps is working fine and would think that gravity would feed the bottom carby which It does when primed prior to starting
I think it’s safe to eliminate pump as I’ve take individual fuel lines off and fuel is pumping
im positive the carby aren’t an issue s as a I’ve had them serviced and swapped
everything from water separator to motor line were replaced
as I’m getting fuel to carbys could it still be an issue before the water separator ie pick up tank and bulb

[boats.net]

To affect only bottom carb. It would probably have to be a blocked fuel hose or float valve sticking closed on bottom carb.