1976 Johnson 70hp stalls at wide open throttle after 20 seconds

[alangore]

after 20 seconds at wide open throttle the engine stalled. checked primer ball at the tank and it was soft and wouldnt pump back up.. checked carb bowls, they were almost empty. I want to replace primer closer to the engine. then replace fuel line, then rebuild the engine fuel pump. Am I on the right track??

thanks,

 

[fireman57]

Make sure that your tank is vented. Might try running with the cap loose first. My primer bulb is down by the tank on my boats. The antisiphon valve in it could be bad.

 

[alangore]

so is the tank suppose to be vented? if I recall correctly every time i remove the cap is seems there is pressure.
thanks,

 

[fireman57]

Yep has to be vented or you stop pulling fuel.

 

[TN-25]

Crack open that gas cap a quarter turn. You should hear a rush of air. Run motor and report back.

 

[Les Robb]

The vent screw on my plastic tank used to vibrate down to the closed position while running. Solved that with a small plastic wire tie placed loosely around the screw.

 

[alangore]

ok finally got back on the water yesterday afternoon. It got up on plane and ran for about 20 seconds and then rpms started going up and down and then it stalled again. started it up again and it continued to do the same thing over and over. im at my wits end.

 

[alangore]

ok back on the water sunday after making more adjustments. found the throttle cable only opening the throttles about 2/3's of the way. fixed it. installed clear fuel line between all 3 carbs. this time it jumped on plane went better but still is running out of fuel. and the primer ball is sucking shut. I took the fuel tank back out. removed the pick up tube and found the plastic piece which would normally be on the cap laying in the bottom of the tank. removed it, curious if it could restrict the flow just enough to cause the bulb suckin shut. Is it possible for the check bals in the bulb to get positioned to plug the line as well???? maybe with the bulb pointing down?? I am going to try to make sure the bulb is up and try it again. anyone have a thought.

 

[alangore]

after 3 more times with same results, bulb sucking shut. OK same issue Sunday on the water, still sucking the primer bulb shut. took the tank out again and found the pick up tube was wedged against a bulge in the bottom of the tank. Even after I have pulled the pick up out about 5 times. I never pulled the tube off the elbow therefore it was always going back in the same place. I have shortened the pickup tube and will try it again this week. cross fingers everyone.

 

[alangore]

. When we got to the ramp, the bulb would not pump up. Took about 10 minutes. and after we got fuel to the carbs, we ran it on the water. It still is sucking the bulb shut. We left and removed the quick connect at the tank, replace the entire fuel line assembly in an atempt to eliminate anything else, even though it is wide open, now when I pumped the bulb it took about 6 pumps and the bulb became firm and had good fuel at the carbs. We are going to try it again tonight or tomorrow night. thanks again for the help.

 

[WernerF]

The bulb's inlet valve could be stuck. Being always exposed to fuel those plasic parts tend to swell over time.

 

[alangore]

The bulb is only about 2 weeks old. I hope they dont fail that quickly.

 

[emdsapmgr]

Is the fuel hose connected properly? Is the arrow on the hose bulb pointing towards the engine? If the fuel pump has enough suction to suck the hose bulb flat, it's likely the pump is functioning properly.

 

[alangore]

yes the bulb is properly installed. I solved my issue last night. I removed the quick disconnect at the tank and installed a barbed fitting. Hooked the line up directly and it runs much better. thanks for the assistance everyone.