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75hp optimax wont start

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Drylander

New member
I have a 2007 optimax 75hp that started to lose rpm then started missing then surging some then died.
I got it home and checked the fuel and air pressure just by turning the key not cranking it was 26 psi fuel and 40 psi air.
Currently the motor start or even hit.
Does anyone have any ideas
 
Start taking a fuel sample from your tank. From the primer bulb, squeeze some fuel into a clear quart container (about 2/3 full.) Check to make sure that there's no water or debris in it. If your fuel is cloudy, you have a substantial amount of water in it. You want to see clean looking fresh fuel. Always do this first to eliminate bad fuel as the source of the problem.

However, your fuel pressure looks awfully low even though you just turned the key on. The high pressure pump will bump up the pressure when you turn the key (usually about 85-90 psi.) Your air pressure won't bump up until it cranks/runs. The air pressure should be about 110-120 psi if I recall.

Spark/Compression test is always a good idea too, just to eliminate those as problems. Take a look at your fuel, and report back if you can.
 
LSXG8GT said:
Start taking a fuel sample from your tank. From the primer bulb, squeeze some fuel into a clear quart container (about 2/3 full.) Check to make sure that there's no water or debris in it. If your fuel is cloudy, you have a substantial amount of water in it. You want to see clean looking fresh fuel. Always do this first to eliminate bad fuel as the source of the problem.

However, your fuel pressure looks awfully low even though you just turned the key on. The high pressure pump will bump up the pressure when you turn the key (usually about 85-90 psi.) Your air pressure won't bump up until it cranks/runs. The air pressure should be about 110-120 psi if I recall.

Spark/Compression test is always a good idea too, just to eliminate those as problems. Take a look at your fuel, and report back if you can.
Click to expand...

Thank you for responding,
This motor has less than 50 hours on it but as been let set for long periods of time if that helps.
I drained the tank after it died on the water and put new gas in it, but the fuel bulb seems soft.
I replaced the pickup tube in the tank.
If it had a crack in the fuel reg or tracker valve wouldnt it still start?
 
With that little hours on the engine I'm suspecting that it's an issue related to the onboard tank/lines. Believe it or not, a bad primer bulb can starve your engine of fuel. If it's one of those cheepy bulbs, I suggest ditching it and going with brand new fuel lines and a Mercury primer bulb. Those ones work the best. What kind of tank is it?
 
LSXG8GT said:
With that little hours on the engine I'm suspecting that it's an issue related to the onboard tank/lines. Believe it or not, a bad primer bulb can starve your engine of fuel. If it's one of those cheepy bulbs, I suggest ditching it and going with brand new fuel lines and a Mercury primer bulb. Those ones work the best. What kind of tank is it?
Click to expand...

I will change the bulb and lines and the pickup tube when i get home.
It is a moller tank.
I will post results tomorrow, everyone keeps telling me its the hi pressure fuel pump because it had ethanol setting in it for so long inbetween uses.
 
this is not the current problem but if that a fairly new 6 gallon moller plastic tank it will not vent with the little vent knob..i think they are playing with the epa on those tanks..i have to just barely crack the fill cap on mine..
 
90lbs fuel pressure and 80lbs air pressure when running. Hook the engine up to a remote fuel tank. Hook up a fuel pressure gauge and see what you get. Of you do not get 90lbs of fuel pressure she will not fire.
 
LSXG8GT said:
With that little hours on the engine I'm suspecting that it's an issue related to the onboard tank/lines. Believe it or not, a bad primer bulb can starve your engine of fuel. If it's one of those cheepy bulbs, I suggest ditching it and going with brand new fuel lines and a Mercury primer bulb. Those ones work the best. What kind of tank is it?
Click to expand...

When cranking the air pressure was up to 80lbs but could only get 30lbs fuel.
I replaced the pickup tube and the hose/bulb( both were bad) and only 2 years old.
I took apart the VSV tank to look at the pumps and it had a dark yellow liquid in the bottom of it.
The screen filter on the bottom of the booster pump was completely full of a dark yellow grit and would run but didnt have much pressure.
The high pressure pump looked ok but didnt seem to hav emuch pressure.
Is their a way to check the pumps with them out and how does this fuel system work.
 
Last edited:
...it had a dark yellow liquid in the bottom of it. ... completely full of a dark yellow grit...
Click to expand...
That's fuel varnish from degraded old fuel. You'll need to clean it out of every part of the fuel system. When it's running be sure to use a fuel preservative like Stabil w/every tank fillup...you never know when the boat will sit for extended periods and untreated fuel begins to degrade w/in 30 days.
 
You will need to clean the VST completely and replace the filter. Now once you have the VST cleaned, you will need to clean the fuel rail, if the fuel in the VST was bad so is the fuel in the rail. While you have the fuel off, pull the fuel injectors and the direct injectors and sen them out for cleaning. DO NOT REMOVE THE ALUMINUM CAPS ON THE FUEL RAIL.

Once the system is cleaned, reassemble, fill with fresh fuel and retest the High Pressure pump.
 
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