fuel psi

[safety20]

hey guys, finally getting everything straightened out on my new motor. if you've read my new motor thread, I figured out my low rpm's. that problem would def be the 14.5x18 prop that's on the boat for some reason. anyways, next question I have, what should my fuel pressure be at idle? I know while running it's supposed to be 30 psi, but i'm not sure for idle. I haven't been able to find any info on that. Right now, with key on engine off, I get 22-24 psi, same thing at idle. but when we open up the throttle while on the water, it'll climb up to 30 and hold. Does that sound normal? I'm probably going to start with changing the fuel pressure regulator. Both fuel filters have been changed. TIA

[chpthril]

Fuel pressure should be the same at idle as it is with the engine at a steady rpm. When you snap the throttle, there should be about a 12psi increase. This reading will be about the same as the key on/engine off reading.

[safety20]

ok thanks man. so I've def got an issue somewhere. like I said, i'm going to start with the regulator and see where that gets me. I appreciate it bud

[boatwakes]

Safety, there's something you need to consider here: that the block you ordered was not set up for the correct horsepower of the Scorpion (320). If the prop was that size, you have a v-drive with a reduction ratio transmission and the boat was originally set up to use that prop. If your original motor had the heads and cam to make 315HP and your new motor is only set up internally for 260-290, that would explain why the prop is now too big. As for fuel pressure, with the engine running at any time pressure should be 30psi +- 2psi per the merc manual. If it's low at idle the regulator may be bad or the hose connecting the regulator to the manifold could be compromised. When replacing the regulator on that fuel pump, you will also want to purchase the brass fuel line fitting that screws into the regulator. It's an extra $35 but well worth it when you realize you've broken the old one trying to remove it from the regulator.

[safety20]

i'm pretty sure the p/o installed the prop that's now on it because it's a stainless. the motor that's in it now was ordered by my local tige dealership as a black scorpion replacement. the size of the prop would def explain my low rpm "issues" that I thought I was having. my boat has only ever run about 36-3800 rpm's at wot which I never paid much attention to before. but now that I am, I know that max wot should be 48-5200 rpm's. i'm not sure how accurate it is, but when I go to wakeprops.com, there chart show's I need a 14.5x14.25 prop where mine is a 14.5x18. I think the correct prop is going to make a huge difference in my boat. it does fine with a few people on it and pulling a boarder, but when it's loaded with 10-12 people, it's like trying to pull a load in a standard pickup in a really high gear. I've already got the brass fitting of the regulator, but I haven't been able to the that fitting of the fuel line lol. I will turn a miniscule amount and then just stop. So far I've managed not to break anything... Knock on wood, lol.

[safety20]

another question for ya man, what would make it low at idle and then come up to 30 when driving? does that sound like a regulator or fuel line issue? tia

[boatwakes]

Regulator for the pressure issue but which fuel fitting are you having trouble with?

[safety20]

The fitting On The Fuel Line Itself That's Not Directly Connected To The Regulator. Sounds Confusing But I'll get A Picture Tomorrow. I Can Get It To Turn Just A Fraction And Then It Locks Up. Like I Said Though, I've Got The RegulatorOff And Haven't Broken Anything Yet So I'll Prlly Just Leave It Alone

[boatwakes]

There are 3 fuel lines on that fuel pump. IF it's the fuel line coming into the top of the fuel cooler assembly, it's held in place with a set screw in the side of the housing, the fuel line itself is not directly screwed into the cooler. There's either an allen head or a small hex head (depends on serial number) stainless screw perpendicular to the outgoing fuel hose located just below the centerline of the fuel line, this is the bolt that needs to be loosened. It has a retainer on the opposite side so you cant lose it but the o-rings on the that line need to be replaced when removed.
If it's the fuel line going into the fuel pump just below the regulator, they're inverted flare nuts so as soon as they turn they should be loose. Post a pic so I can see which one.

[safety20]

its The Line Coming OfF The Regulator, But Not The Fitting Directly ON The Regulator. I'll Get A Picture This Afternoon. Thanks For Your Help

[safety20]

Its this fitting on the end that goes on to the regulator.


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[boatwakes]

Okay, so you've got the 5/8" wrench on the hardline side and then the 11/16" wrench on the adapter side (the fitting that goes into the regulator) and you turn them away from each other. From what I read of your previous posts I just want you to be aware that there are 2 separate fittings there (you may already know but I'm just clarifying). If you cant get them apart, you may have to buy a new hose and a new fitting, which are available, but that allows you to wrench on it without too much worry of not having a replacement part. Keep at it.

[safety20]

I never was able to very those two fittings apart. I got them to turn a little bit but that's all. They would never unscrew from each other. Anyways I was able to get the new regulator installed without separating them. I appreciate all the tips from you guys. My next protect is changing out my prop. I'm going from a 14.5x18 stainless prop to a 14.5x14.25 oj prop. I have no idea why someone would put a prop with a 18 pitch on a boat this size, much less a stainless one. Lol that's just adding for trouble, especially in my lake that is 12 feet low.

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[TeamAllen]

Glad you got the regulator completed. Did you look at the ACME Propellers?

[safety20]

I did, only reason I went with the oj is I was able to pick it up for about half price being that it is used but looks new. Should feel like a new boat with the prop swap.