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2003 Johnson 175 HP Starving/running out of fuel at speed

J

Joe McDonald

New member
Been having intermediate fuel issues with this motor for sometime. Started out with idling issues stalling at the dock, burning very rich. Motor would run on the trailer, but seemed to stall out with exhaust back pressure. The carburetors, VRO was rebuilt and seemed to run a little better. A few months ago the motor was running good under power, started to stumble and seemed to be running out of fuel when attempting to come up on plane. This occurred a couple of times, but re-priming with primer ball cured the problem.... only temporarily. Thank god for twins.
I have now rebuilt the fuel/vapor separator, including replacing needle and seat, the diaphragm and gaskets. I checked all fuel and pressure lines, all clamps replaced. The carburetors had wrong orifices (0.30) the correct 0.39 were put in the carbs. The fuel primer ball and fuel line were replaced.
Motor ran great on the trailer, at the dock, powered up and brought up on plane the motor stumbled, slowly running out of fuel, primed the motor and rpms came up, ran for 30 seconds and repeat. This went on for ten minutes. After one of the re-primes the motor ran good on plane at 3,500 rpm for approximately 10 minutes or so. Entered a slow speed zone, throttled down. That was it for the day, back to re-priming the motor the entire return trip. At the dock, would idle at 1000 rpm forever, on the trailer motor ran good during flush out.

Please help
Thanks - Joe
 
Faztbullet
Thank you for the quick response to my issue. You have provided me with valuable information in the past couple of years that has been spot on correcting my motor issues. My issue became worse after the rebuilding of the VST and the vacuum pump, the diaphragm, gaskets were replaced and seated during assembly. Upon testing for leaks, I located appears to be a very tiny relief hole between the VC housing plates that faces the motor after assembly. A vacuum test of a small intake nipple, top of VC, allowed air to be sucked in through this hole. Is this normal or maybe my problem.

A second set of diaphragms and seals inspected and placed in VRO - same problem exists. No issues prior the primer ball, the ball does not get sucked flat, can push fuel to the motor to run, motor will not suck fuel on it own to maintain RPMs

Thanks Joe
 
Be mighty careful if you try this as there is not a nipple on IN side of VRO...lot easier to put a electric fuel pump one line so it feeds VRO.
 
It draws it from bottom of VST reservoir.. sealed with o-ring on VRO and slip fit with o-rings into fuel bracket. Hose will not slip over and seal this nipple.
 
Last edited:
faztbullet said:
It draws it from bottom of VST reservoir.. sealed with o-ring on VRO and slip fit with o-rings into fuel bracket. Hose will not slip over and seal this nipple.
Click to expand...
if you look at a parts breakdown you more learn that this item goes on top of vro and is the fuel outlet. For reverence,the fuel IN has always been on the bottom.
 
Guys
If I plug the outlet fuel line from the bottom of the VST that feeds the lower inlet nipple of the VRO, then removing the main fuel line from the filter inlet at the VST, and re-connect the main fuel line to the lower inlet nipple of the VRO should by-pass the function of the vacuum pump (VST) allowing the VST tank to fill and feed the outlets to the fuel rails. Do you think this will resolve my issue without causing damage or engine malfunction.

Your thoughts, you'll sound as if you've addressed this problem in the past. - HELP

Thanks for your help - Joe
 
Joe McDonald said:
Guys
If I plug the outlet fuel line from the bottom of the VST that feeds the lower inlet nipple of the VRO, then removing the main fuel line from the filter inlet at the VST, and re-connect the main fuel line to the lower inlet nipple of the VRO should by-pass the function of the vacuum pump (VST) allowing the VST tank to fill and feed the outlets to the fuel rails. Do you think this will resolve my issue without causing damage or engine malfunction.

Your thoughts, you'll sound as if you've addressed this problem in the past. - HELP

Thanks for your help - Joe
Click to expand...
The VRo is mixing your fuel,we simply are bypassing the vst.the vst .tank does not fill. Will it resolve your issue,I don't know,if it does we know you have somthing wrong with your vst.
 
Faztbullet,
I'm going to loop the VST bottom outlet fuel line and connect directly into the filter inlet. I will then reconnect the main fuel line into the VRO fuel inlet nipple in an attempt to bypass the VST. In theory, the VRO should pump the fuel mixture into the VST tank, feeding the fuel rails for the carbs. Sound like a plan?????

Joe
 
Looking back over post,have you done fuel pump pressure test? Installed clear fuel hose and watched fuel flow? Compression test?
 
Thanks for asking, not good.
Replaced Vacuum Pump, took mthe boat and the same thing. Runs out of fuel at high RPM/Speed. Will run if you contine to use primer ball under power.

While on the trailer, motor runing, the fuel lines were taken loose at the VST top plate (going to fuel rail/ carbs) and the fuel barely flowed from fittings. If the primer ball is squeezed, the fuel will shoot 5 feet. I'm losing my mind.

Compression 75 psi all cylinders, checked or replaced all pressure/ fuel lines for damage/looseness. New fuel lines, water/fuel separators, primer balls, VST and VRO rebuilt.
 
Joe McDonald said:
Thanks for asking, not good.
Replaced Vacuum Pump, took mthe boat and the same thing. Runs out of fuel at high RPM/Speed. Will run if you contine to use primer ball under power.

While on the trailer, motor runing, the fuel lines were taken loose at the VST top plate (going to fuel rail/ carbs) and the fuel barely flowed from fittings. If the primer ball is squeezed, the fuel will shoot 5 feet. I'm losing my mind.

Compression 75 psi all cylinders, checked or replaced all pressure/ fuel lines for damage/looseness. New fuel lines, water/fuel separators, primer balls, VST and VRO rebuilt.
Click to expand...
Read post #2.
 
While on the trailer, motor runing, the fuel lines were taken loose at the VST top plate (going to fuel rail/ carbs) and the fuel barely flowed from fittings. If the primer ball is squeezed, the fuel will shoot 5 feet. I'm losing my mind.
​
Click to expand...
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A VRO pump will not constantly pump fuel like a standard pump. It only pump when you hear the "click" of pump. When motor is at idle lay your hand on front of air motor of VRO cover and you should feel and hear it click in under a minute. If not the VRO has a problem on air motor side, the check valve in VRO inlet is bad(replace VRO) or crankcase compression to low to create pressure/vac pulse to overcome spring in VRO.
 
I'm going to check the VRO air motor side tomorrow morning for the click of the VRO. How can I check for crankcase compression/vacuum. I replaced the block 2 way valve last week...

Thanks - Joe
 
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