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Fuel line size not enough fuel?

Tahoe540

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I have just swapped a stock 454 to a pretty stout 555. I finally got it out and was expecting this motor to pull harder and turn some rpm. It hits a wall and just stops pulling around 4800 rpm. The motor should be around 650 HP. Same setup with 099 iron heads dynoed at 621 HP. It now has Brodix BB2 heads with shaft rockers and is 10:1. The stock motor pulled 4800rpm with the same pump.

I have a B/G pump that was rebuilt with a new stainless A, droop and a ride plate. The boat is a 21ft Hallett daycruiser.

I left the fuel lines in the boat and they are 3/8 hose all the way to the carb from the fuel tanks. I have read this could be a fuel starvation issue on the top end.

What I am planning
Because my lines from the tanks are only 3/8 I was going to run both tanks at the same time into a new filter head with 1/2 NPT threads. From the filter head outlet I was going to run 1/2 hose all the way to the carb. I am planning on buying a new 170gph pump and plum it with -8AN fittings to 1/2 hose barbs. I have also installed a new 1050 (4150 plate).

I am open to any suggestions or ideas why it is hitting a wall. This same combo pushed my 30ft Advantage offshore boat to 60mph at Lake Tahoe (6000 ft elevation).
 

rivrrts429

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What cam and at what RPM is it making peak HP?
 

rivermobster

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I'm going to say 3/8 is way too small. But, have you put a fuel pressure gauge on the carb to verify??

I had to deal with this condition and ended up with a fried engine from going to lean.

Imco makes new fuel tank fittings that are -8 straight from the tank. You don't want to lean out a new engine and fry it...
 

Tahoe540

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What cam and at what RPM is it making peak HP?
I have not dyno'd the new setup but this is the dyno with the iron heads. I have also installed solid lifters.
DynoGraph.jpg
 

vstdispatch

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I had a 540 and it had -10 from tanks to pump then -8 to carb which was more than enough fuel. I think you would be fine with -8 from tanks to pump and then -6 to carb
 
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ElAzul

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What's timing currently set at?
 

farmo83

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I would verify your anti siphon valves aren't sticking somewhat and restricting the flow.
 

jones performance

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maybe try bigger needle and seat assembly first.. unless you already got the biggest ones in it then step up fuel line size for sure. like asked above, whats your total timing at?
 

Tahoe540

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I am running a Davis Unified HEI. The initial is 14 and I am all in at 34. I have tried 32 and then up to 38 with pretty much no change. I was expecting it to pick up with the extra timing but it did nothing except for hard to start.
I am running a brand new proform 1050 4150 square plate. I have not messed with the carb yet.
 

Tahoe540

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I am also buying a new fuel pump that flows 130gph as I don't know what the current one is.
 

obnoxious001

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I have just swapped a stock 454 to a pretty stout 555. I finally got it out and was expecting this motor to pull harder and turn some rpm. It hits a wall and just stops pulling around 4800 rpm. The motor should be around 650 HP. Same setup with 099 iron heads dynoed at 621 HP. It now has Brodix BB2 heads with shaft rockers and is 10:1. The stock motor pulled 4800rpm with the same pump.

I have a B/G pump that was rebuilt with a new stainless A, droop and a ride plate. The boat is a 21ft Hallett daycruiser.

I left the fuel lines in the boat and they are 3/8 hose all the way to the carb from the fuel tanks. I have read this could be a fuel starvation issue on the top end.

What I am planning
Because my lines from the tanks are only 3/8 I was going to run both tanks at the same time into a new filter head with 1/2 NPT threads. From the filter head outlet I was going to run 1/2 hose all the way to the carb. I am planning on buying a new 170gph pump and plum it with -8AN fittings to 1/2 hose barbs. I have also installed a new 1050 (4150 plate).

I am open to any suggestions or ideas why it is hitting a wall. This same combo pushed my 30ft Advantage offshore boat to 60mph at Lake Tahoe (6000 ft elevation).

Altitude is not helping you, depending on where it dynoed you won't see that much power, maybe drop 10% (Don't hold me to that number) . Then look at what power you would be making at 4800, the pump acts like a dyno and limits your RPM. Did you adjust jet sizes for the 6,000 feet (3 sizes smaller)?
 

Tahoe540

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I am now boating at a lake that is around 4500 ft. The dyno was taken at 4800ft. I have not messed with the jets yet as I have only taken it out once. I took the carb out of the box and ran it. I believe they jet them for sea level. I have 2 of those jet boxes from Holley. I have a lot of jets to try. My stock 454 was a few miles per hour slower and the rpm for the 555 is only about 1-200 rpm. This thing falls on its face at 4800.
 

Riverbottom

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I would verify your anti siphon valves aren't sticking somewhat and restricting the flow.

This !!! Been through this a few times. They won't flow enough fuel. Friends pontoon boat just quit running day before. Running lean, took out anti siphon valve and it runs better than it ever has. Check these first.
 

mash on it

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This !!! Been through this a few times. They won't flow enough fuel. Friends pontoon boat just quit running day before. Running lean, took out anti siphon valve and it runs better than it ever has. Check these first.

On my Saguaro squirt botë, the flip top fuel fills didn't allow for air coming in, and the engine would struggle to keep a constant rpm after a few minutes.

I would open the cap after a short run, and the tank would equalize. (vacuum in the tank) Right or left, it did the same thing. A tiny hole under the cap cured it. (Carter electric fuel pump)

Maybe something to check out.

Dan'l
 

Tahoe540

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Will a bad anti siphon valve cause the carb to flood the engine after you turn the motor off?
 

DarkHorseRacing

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No, the carb's floats should shut the needle seats down when the bowls are full. I don't think unpressurized fuel in the lines would override the bowl floats and needle seats. You could take the air cleaner off and watch the motor, if it happens you can see it, it should come out the bowl vents.
 

BamBam

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"Stops Pulling" or "Falls on it's Face" you said both and to me those are two totally different things
How much fuel pressure are you running and how far does the pump have to draw from the tanks?
Are you losing fuel pressure at 4800RPM?
 

DarkHorseRacing

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You would think if it was a loss of fuel pressure that the motor would lean out and possibly backfire and that would be a dead giveaway.
 

rivermobster

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You would think if it was a loss of fuel pressure that the motor would lean out and possibly backfire and that would be a dead giveaway.

Doesn't always work that way, especially at high rpm. And all it has to do is run lean enough to increase the cylinder temps. Then say goodbye to your pistons...
 

Streetmoto

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I'd have a fuel pressure gauge plumbed right before it enters the carb and confirm you have a flow/pressure issue before replacing anything else. Might be a long shot, but I had a similar issue happen with one of my old v-drives and it ended up being a little water in the fuel. At full throttle, it was draining the float bowl and getting into a little water that had accumulated. Might be worth draining a float bowl into a clear water bottle so you can cross that off the list as well. Good luck!
 

Tahoe540

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I installed a new fuel pump, new high flow fuel filter and also added a fuel pressure gauge as I did not have one. The summit fuel filter I had installed was not a high flow besides having it in backwards . I don't think this helped the situation
The fuel pressure read 7psi at idle. I also got a new timing light. I looked at my paperwork I got with my distributor. It says I have 24 degrees that comes in at 3000r pm. I checked what initial timing it had and it was running 22 initial . I now have it set at 10 degrees initial for a total of 34 degrees.
The carb is not flooding the engine when I turn it off now. I can turn it off and back on and it fires instantly.

I have not taken it out yet to see how it runs. I hope I have time tomorrow
 

Mcchevy69ss

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Check your fuel pressure at WOT if possible. That will give you clear indication of the fuel system ability. If you don’t maintain at least 5+ psi you need to go through your entire system and make sure you have at least -8 line size, and appropriate sized pump (120gph or bigger). If all is well, I would verify plug readings and jet accordingly.
 

rush1

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Don't forget the fuel tank selector valve needs to be 1/2" too
 

Tahoe540

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It never popped or sputtered at 4800rpm WOT. It just stopped pulling.
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I did pull the motor to install a new cam and have the heads freshened. I found almost all the valves are white. From what I read this is a lean condition.
 

rush1

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Yep it's lean ,aluminum heads pull a lot of heat out of the engine .I ran into the same problem when I put aluminum heads on my jet boat .I changed all of the fuel lines ,fuel pump,and tank transfer switch to all 1/2" and made sure the tank pick ups were 1/2" to solve the problem
 

Tahoe540

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Yep it's lean ,aluminum heads pull a lot of heat out of the engine .I ran into the same problem when I put aluminum heads on my jet boat .I changed all of the fuel lines ,fuel pump,and tank transfer switch to all 1/2" and made sure the tank pick ups were 1/2" to solve the problem
Thanks for that info.
I am planning on doing a 1/2 inch fuel system over the winter now. I am not looking forward to upgrading the tank pickups to 1/2"
 

Husqy510

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Install a FP pressure gauge at carb. Our 540 makes 720hp and we're utilizing stock 3/8 pick ups and we're sustaining 5.5lbs at WOT.
 

shan

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What regulator are you using? I agree with everyone else here, if you don't know the pressure at the carbs, you're pissing in the wind.
 

Tahoe540

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I did install a cheap summit pressure gauge in the port on the feed line. Full throttle showed 6-7 as close as I could tell. It was hard to tell because it was bouncing so much.
I did not run a regulator on the mechanical pump.
 

Husqy510

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If you have over 5lbs at the carb, fuel pressure is not your problem. Could simply be a lean issue, what jets are you running?
 

Tahoe540

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It is lean for sure. The valves are white.
I have tested the throw I am getting full throttle.
The fuel pressure is as good as I can tell. At wide open the needle bounces between 3.5ish to 6.5 ish. The needle is bouncing so much it is hard to tell so I went with the middle.
I went one jet size smaller than what the carb came with. I boat around 4200 feet.
 

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