Fuel line size

argosy40 · Oct 18, 2017

I just a 68 and noted that it has the nylon 5/16 fuel line from tank to fuel pump. Seems too small. Should that line be steel and 3/8 or?

I ask as the 289 bogs down under load and perhaps the small line is starving the fuel ???

Any help would be appreciated.

AZ73 · Oct 18, 2017

What kind of carb are you running?

BUCKWILD · Oct 18, 2017

My 289 made 350+ hp and the 5/16 line was fine. You might have a kink or obstruction in yours or a carb or distributor problem

argosy40 · Oct 18, 2017

Fuel line

Carb is a Holley Demon , model 1901, 625 cfm.

Timmy390 · Oct 18, 2017

Stock 289? That carb is a bit big for a stock 289 IMO. Rule of thumb state 1.8-2 CFM per engine CID for a performance engine. That comes to 578 CFM for a 289 using the high end of that basic CFM estimate. I bet your running rich.....

My guess is it's bogs when the secondaries kick in......Maybe change the jet size ( bit smaller) and see how she runs.

Tim

AZ73 · Oct 18, 2017

Your carb is a little big, but should be OK because in theory, it's not running 625 unless it needs it. Your Demon is a vacuum secondary so I don't think you have a richness problem unless you have your secondaries mechanically open by having a screw on the linkage? Pull your air cleaner off and, with the motor off, use your hands to move the throttle linkage. Your secondary's shouldn't move at all. If they're linked to the primary and they move, you're bogging down with gas.

Another problem might be air getting into the line. If its the original fuel line, see if it's leaking or cracked. At 50 years old, I'd replace it anyway.

Broncobowsher · Oct 18, 2017

If the fuel line to the carb is the limitation (this includes filters) You should be able to lift off the thrttle for a couple seconds (keep the RPM up) and stab the throttle agian and it will run great for a couple seconds before falling down again. The closed throttle gives a chance for the fuel bowls to refill and it should run great again until the bowls are sucked dry again.

Fuel filters are more likely a restriction. Not just the one at the carb, there is typically a filter sock on the pickup in the tank as well. They do clog sometimes.

My guess is a carb problem that you are looking elsewhere for.

DirtDonk · Oct 18, 2017

Describe when exactly it's bogging down. As the others have said, the stock line was enough for the power level of the engine back in the day, plus some leeway.
If you're bogging down after a long uphill slog or full-throttle blast, that could be a fuel delivery problem. But if it's bogging down any time you accelerate, that's a carburetor, vacuum leak, or ignition issue.

Nothing wrong with changing the old line to new and/or larger line, but if that's not the issue you'll do a lot of work for nothing.

Is this Bronco new to you? Or have you had it awhile? Sounds like you just got it (but not sure) and if so, has it done this from day one, or did it start all of a sudden?

Thanks. Good luck.

Paul

AZ73 · Oct 18, 2017

BTW, I got a new BC Bronco carb fuel line I'm not using. Oceanside isn't too far. I'm in riverside a lot or could ship. Call it $40 plus shipping or you come to riverside next time I'm there.
I believe this was the kit:
https://bcbroncos.com/shop/fuel/fue...-carb-fuel-line-only-1-tank-for-early-bronco/

DirtDonk · Oct 18, 2017

Those are very nice kits if you're wanting to get away from the nylon.
My nylon was in great shape, but not all are.

Paul

PaveBronco · Oct 19, 2017

argosy40 said:
Carb is a Holley Demon , model 1901, 625 cfm.

is a bit big, unless you're running 6000rpm all day long.
You can try doing some tuning.
http://documents.holley.com/lit701rev10.pdf

or sell it to a hot rodder and buy something smaller that's more drivable, maybe a 500 or 550cfm.

ntsqd · Oct 20, 2017

Assuming that it isn't a carb tuning problem the first thing that I'd do is replace all of the rubber fuel hose. One failure type of rubber hose is flaps inside that block flow. They're usually free to move around so they only block flow at high demand. If the hose is harder than when new or softer than when new it's past time to replace it anyway.

It is more expensive, but the "emissions barrier" hose has a liner in it that will prevent this from happening again.

taipeichris · Oct 20, 2017

Hi Guys,

If not the carb, I'm thinking he's got crap in the tank. My 66 sat for a while and had a similar problem when I first started it. I disconnected the line before the fuel pump, shoved it in an old coffee can, bypassed my rear fuel filter and blew compressed air into the filler tube of the main tank and a lot of fine sandy dirt flushed out.

Concerning the fuel lines. I got rid of the plastic lines a long time ago and ran metal lines with minimal rubber lines connecting them. Do it once, do it right, don't get stuck doing it again. Spilled gasoline stinks.

Good luck and check your filters too!

PS Thank you to the guy who posted this brake line double flaring tech write up. It was super helpful and made flaring my fuel lines easy!
http://classicbroncos.com/tech/brake-line-double-flaring

ntsqd · Oct 20, 2017

Unconvinced that metal lines are the best effort. Modern fuels have enough alcohol in them that they will also have more than 'normal' moisture in them. When I did all new fuel lines I made a point of not using materials that can rust as cad plating just isn't what it used to be. I used nylon tubing for the long lengths of both the supply and the return. I think Ford had that right, just that their end connection methods were less than robust.

Broncobowsher · Oct 20, 2017

Just pulled some fuel lines off a 2017 truck. There were metal, with nylon on the ends.

ntsqd · Oct 20, 2017

What was the ID lined with?

Broncobowsher · Oct 20, 2017

ntsqd said:
What was the ID lined with?

No idea, didn't cut them open. And they didn't look like stainless on the outside either.

ntsqd · Oct 21, 2017

yea, doubt that they'd be SST, but I'll venture that they are lined with a polymer of some sort. Much like the new brake tubing is polymer coated.

Fuel line size

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