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Discussion Starter · #1 ·
Hey all, new here but seeking help, please.

1985 E350, de-smogged 460ci, new dual tanks and pumps including frame rail booster, fairly new Holley 600cfm, new Holley pressure regulator @9#'s. Tanks are full of fuel.

Starts and runs great at lower speeds, but on acceleration (opening secondaries) to highway speeds, starts chugging and acting like not sufficient fuel. If I pull over it recovers, but starts again after 3/4 mile.

Fresh out of ideas, and tired of using parts cannon.

Help please?

Kimberly
 

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Hey all, new here but seeking help, please.

1985 E350, de-smogged 460ci, new dual tanks and pumps including frame rail booster, fairly new Holley 600cfm, new Holley pressure regulator @9#'s. Tanks are full of fuel.

Starts and runs great at lower speeds, but on acceleration (opening secondaries) to highway speeds, starts chugging and acting like not sufficient fuel. If I pull over it recovers, but starts again after 3/4 mile.

Fresh out of ideas, and tired of using parts cannon.

Help please?

Kimberly

Filter plugged?
 

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Sounds like to small of fuel lines. You could a 100 gal tank with 300 gal per minute pumps trying to push fuel thru a 1/4" line. Ain't goin happen. 600 is a bit on the small side and it follows as much fuel as it will get. Problem is getting it there. Check for bent lines that are a restriction to.
 

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Discussion Starter · #5 ·
Sounds like to small of fuel lines. You could a 100 gal tank with 300 gal per minute pumps trying to push fuel thru a 1/4" line. Ain't goin happen. 600 is a bit on the small side and it follows as much fuel as it will get. Problem is getting it there. Check for bent lines that are a restriction to.
Hi Dacofa,

The fuel lines match original and are new almost from tank forward. 3/8 on main, 1/4 on return lines.

Had it in a shop this last week because I have no fuel pressure guage, and he said pressure was low after the regulator which is also the fitting for the return line to tanks. So he replaced the regulator with a Holley adjustable and measured pressure at carb at 7# I think, max I for a carb I understand.

600 was suggested by Holley, and if this was a performance engine I would have gone 750 for sure. But it is just an old RV and never has big demands, and is about the same size as the original Ford carb. Just a highway cruiser but doesn't even want to do that.

Float problem maybe?

Kimberly
 

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You say you have a pressure regulator. Dead head or bypass?

A non return FPR can restrict fuel.









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If you are positive you have good fuel volume (test per the factory manual procedure for volume into a container if not), then you are into the fuel delivery (carb) for issues. If it always happens under the same conditions, then your ignition needs a check-out also. I had one similar-sounding case, that had a broken muffler baffle partially blocking the muffler outlet. There are too many potential issues to throw parts and cross fingers.

A vacuum gauge and knowing how to use it can be helpful in diagnosing the general direction of the issue, as can other diagnostic tools or tests, to find or eliminate likely problems based on symptoms. Your goal at this point is info and clues to guide you. Diagnostics. The alternative to throwing parts at it is diagnosing what parts or work to throw at it. The up-side is that diagnostics are typically quicker and cheaper than the parts cannon.
 

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Discussion Starter · #11 ·
If you are positive you have good fuel volume (test per the factory manual procedure for volume into a container if not), then you are into the fuel delivery (carb) for issues. If it always happens under the same conditions, then your ignition needs a check-out also. I had one similar-sounding case, that had a broken muffler baffle partially blocking the muffler outlet. There are too many potential issues to throw parts and cross fingers.

A vacuum gauge and knowing how to use it can be helpful in diagnosing the general direction of the issue, as can other diagnostic tools or tests, to find or eliminate likely problems based on symptoms. Your goal at this point is info and clues to guide you. Diagnostics. The alternative to throwing parts at it is diagnosing what parts or work to throw at it. The up-side is that diagnostics are typically quicker and cheaper than the parts cannon.
Thanks PSIG all good suggestions,

My mechanic has checked pressures which led to the regulator replacement which showed low function.

Timing/dwell/advance have checked out, exhaust has good flow. Has had new plugs/wires/cap/rotor recently and a new coil. What else in ignition would cause this?

I was catching up on 10 years of maintenance in 6 months as it sat for many years only being run occasionally.

Thanks again,

Kimberly
 

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Discussion Starter · #12 ·
Do you have another carb to try?
Do you know the need of dbl bowls on the Holley street carbs? Does one supply the primary side and one the secondary side?

Question- If there is an issue with the bowl needle on the secondary side, and full acceleration depletes the secondary bowl, would it starve the primary bowl of fuel trying to refill the secondary bowl?

Would this lead to the starvation of fuel in primary bowl after hard acceleration, but recovery after 30-40 seconds of low engine speed and lower fuel consumption?
 

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Do you know the need of dbl bowls on the Holley street carbs? Does one supply the primary side and one the secondary side?

Question- If there is an issue with the bowl needle on the secondary side, and full acceleration depletes the secondary bowl, would it starve the primary bowl of fuel trying to refill the secondary bowl?

Would this lead to the starvation of fuel in primary bowl after hard acceleration, but recovery after 30-40 seconds of low engine speed and lower fuel consumption?

If for some reason it was I believe it would recover with a few seconds with normal fuel pressure. Does this have seperate feed lines to the bowls or the transfer tube from the primary to secondary?
 

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Discussion Starter · #16 ·
Couple other things to check. Is the throttle blades fully opening? I didn't see it mentioned but if this is a vac secondary is the diaphragm stuck?
Those two things appear to be functioning. I called Holley this morning, they suggested the fine mesh screens at the banjo fittings where the fuel lines enter the bowls may be clogged. They also said to test the vacuum level of the intake system to confirm the proper power valve is installed. I measured 13-15 in/Mg which would justify the 6.5 power valve installed as standard.

Good thoughts though, thanks

K
 

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Might have a chunk of gas line just before a needle & seat. When fuel demand is high, fuel pressure pushes it toward the needle until it obstructs just enough fuel flow to cause this. Shot in the dark, for sure, but it has happened. To me. Made me say something my mother would not have approved of. Sometimes hard to find but an easy fix.
 

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Discussion Starter · #18 ·
Might have a chunk of gas line just before a needle & seat. When fuel demand is high, fuel pressure pushes it toward the needle until it obstructs just enough fuel flow to cause this. Shot in the dark, for sure, but it has happened. To me. Made me say something my mother would not have approved of. Sometimes hard to find but an easy fix.
We have narrowed it down to a lack of adequate flow at the carb, while having sufficient pressure. The engine requires about 18oz/min but is providing about half of that. Next we check flow at various points back to the tanks. At the rail pump and filters, then the tank selector, then the individual in-tank pumps.
 

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We have narrowed it down to a lack of adequate flow at the carb, while having sufficient pressure. The engine requires about 18oz/min but is providing about half of that. Next we check flow at various points back to the tanks. At the rail pump and filters, then the tank selector, then the individual in-tank pumps.
I think I have replaced twenty pounds of tank transfer switches.Run without the caps for a bit.Then plumb in the old never dies brass handle selector valve.
 
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