Logo
FULL SITE MENU

1988 Johnson GT 175 Fuel Delivery Issue

J

jtecker

Member
Trying to isolate fuel issues with this motor that came with an old Mako I purchased. Problem is engine is stalling out when trying to get up on plane but works fine when pumping the bulb constantly. Bought a new fuel line/pump combo line and a new see-through in-line filter. Ran motor from an auxiliary tank with a clean mix of fuel to rule out old boat tank issues. When idling, the fuel is not much more than a drip coming out of the fuel line from the tank and being pulled through the bottom of the filter to the motor. If I pump the bulb the filter fills up a little over half way but after about 15 seconds is goes back to basically being empty. Shouldn't that filter be at least half full at idle? I have a feeling if I took it for a ride I'd see that filter completely emptying out when trying to get up on plane. For reference this motor had the VRO pulled at some point and replaced with an EMP brand pump that appears to be fuel only. The pump works off of the engine pulse and is not electric. I've taken the pump apart and inspected all ports, diaphragms and gaskets and they appear to be fine. What could be causing this very weak pull of fuel? Engine not pulsing properly? Bad pulse limiter? Vacuum issue somewhere on this motor I haven't considered?
 
The pulse limiter is a " flow fuse " for the VRO pump.----May not be needed for your pump.-----Do a compression test and post your numbers.-----That may give a clue on your issues.-----Fuel pump is driven by crankcase PRESSURE.-----There may be an issue there.
 
racerone said:
The pulse limiter is a " flow fuse " for the VRO pump.----May not be needed for your pump.-----Do a compression test and post your numbers.-----That may give a clue on your issues.-----Fuel pump is driven by crankcase PRESSURE.-----There may be an issue there.
Click to expand...

Is there a way to measure the crankcase pressure at the output point that drives the pump? I checked compression a month ago. It was strong and even on all cylinders but I don’t remember the numbers.
 
You can have good compression in the cylinder , but zero compression in the crankcase.-----What pump do you have on this motor.-----Part # or picture ?-----Before the VRO in 1984 the 83 model V-6 used 2 pumps in series.
 
It’s one of the EMP fuel only replacement pumps. The VRO system was removed at some point in this motors past. Trying to post a pic but having issues on my phone
 
Back
Top