Carbed 6.0 LS fuel pump

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Beebo
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Carbed 6.0 LS fuel pump

Post by Beebo »

I am running a carbed 6.0 LS on a 15" aluminum boat. The motor has run amazing since the original build one year ago. However, I took it out this past Saturday and it ran like crap, backfired, and lost power when under load and accelerating. At idle it purred like a champ, and at WOT I couldn't notice any changes or deficits. I'm thinking fuel pump. I unplugged all spark plugs and all coil packs and with each, a noticeable change occurred with engine idle. I'm thinking the fuel pump may be the culprit, but I have limited experience with issues like these. I am running a summit brand external fuel pump, 105 GPM with a maximum of 14 PSI. I swear it was running 11-12 pounds of pressure before this weekend, and now it's running around 7-8 pounds. All that being said, I am going to order a new fuel pump and wanted to ask for recommendations for a carbed LS airboat motor. My boat runs 95% saltwater and is primarily a fishing boat. This does expose it to the crud and elements of saltwater.

Gary S
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Re: Carbed 6.0 LS fuel pump

Post by Gary S »

I think I would check filters first.

One Eyed Gator
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Re: Carbed 6.0 LS fuel pump

Post by One Eyed Gator »

One thing to check is the caps on the vacuum ports. The black rubber caps don't last very long. I use the silicon style and just had to replace one one those.

If you are running a holley this is from Holley website
A. FUEL PRESSURE: This carburetor has been designed to work best at fuel pressures between 5 and 7 psi. Holley recommends 7 psi at idle, and a minimum 4 psi at engine redline.

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Deano
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Re: Carbed 6.0 LS fuel pump

Post by Deano »

First of all, don't overlook the good advice you have already been given.

If your current pump is 14 psi capable and is in fact producing 11-12 psi,
replacing that pump first, most likely will not address your problem.
You didn't say if you are or are not running a fuel pressure regulator with that pump.
If not, based on your description it would appear that you should be (at least with that pump).
If you are, it appears that the regulator isn't regulating and is where your problem most likely lies, not with the pump.

You didn't say what make or size carburetor you are running. In any case, be aware that most
carbs generally do not need/want > than 7 psi in order to operate as designed (and some less).
Round ball park numbers ---
Edelbrock : wants 5 - 5.5, with 6.5 max
Quick Fuel : wants 6.5, with 7 max
Holley : wants 5 - 7, with 7 max

If your current pump is minimally producing nearly twice what is needed, that is not likely the issue.
Based on your descriptions, the odds seem best that you have to much of a good thing.
This premise may be supported by your stating that, in spite of the other weirdness going on, it runs good at WOT.
With the increased fuel demand, the pressure may be dropping to what the carb can happily deal with.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

Gladesman06
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Re: Carbed 6.0 LS fuel pump

Post by Gladesman06 »

I agree with Deano 100%. A carburetor is not designed to have over 8psi. You have a good chance of flowing pass the needle and seat with pressure over 8psi. This will then cause the float to not be able to shut off the flow of fuel to the bowl. This might not happen right away but over time it will definitely cause you problems. Yes you do need some pressure but volume is needed also. I see it to many times in the airboat world that there is pressure to the carb but the 3/8 hose isn't giving enough volume to keep the bowl full while wide open. I'm not saying at all this is your problem, I'm just giving you advise that might help you in the future. I will say I don't believe your pump is bad at all because if it was it wouldn't be running good at wide open. In my opinion it is something with the carb. You might want to check the power valve in the primary bowl. The secondary bowl most likely has a blocked power valve. You might also want to check the squirter to make sure it's squirting fuel the way it should.

victorg
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Re: Carbed 6.0 LS fuel pump

Post by victorg »

Check to make sure your secondary butterfly's are opening and make sure they are squirting fuel.

Had the exact issue on my carved 6.0. Ran great at idle, had proper presure, but when I opened it up, it would pop, and backfire.

The secondary jets were clogged, and no fuel was coming out, so when the butterfly opened and no fuel went in, only air was introduced to the mixture creating a super lean condition.

Beebo
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Re: Carbed 6.0 LS fuel pump

Post by Beebo »

I am running a Quick Fuel SS-Series 650 and a Holley 4-9 PSI fuel pressure regulator. I am going to back the pressure down to 6 this afternoon and also check the squirtors. I pulled my plugs and they are all covered with black soot. I will post a picture if I can figure that out. And I will check the vacuum caps and make sure they are in place and operable.

Beebo
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Re: Carbed 6.0 LS fuel pump

Post by Beebo »

Replaced fuel pump, pressure regulator, and plugs. None of those helped. I became quickly frustrated and began looking for any source of excess air. After checking my intake and carb bolts, I found 5 that were lose, not falling out lose, but 2-3 turns lose. I tightened them up and prayed for the best. I took it out the next day and it never missed a beat. Lessoned learned, check the small things first!

CarMotorBarge
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Re: Carbed 6.0 LS fuel pump

Post by CarMotorBarge »

You need to put blue lock tite on those bolts. Vibration from the prop loosens stuff over time.
14x7.5 Al David hull with 14 inch transom
419 CI Horsepower Barn LS3 with 2.88 Ox Box swinging 4 blade 83.5" R
GTO Rigging and B&S Tilt Trailer

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