Fuel supply issues

blknblu69v · Apr 27, 2017

69 Bronco, 302, new electric fuel pump/regulator, psi gauge. About 6# psi going to carb via in line fuel filter. Filter does not get over 1/3 full. When engine is hot, I get unstable idle and fuel psi drops to 2# then back up and down. Running on rear tank. Starts hard when hot and near empty filter. Could this be a clogged fuel pick up in the rear tank? Newer plastic tank installed during restoration. Hasn't ran right since, just dealt with it.
Thanks for your help!!

pcf_mark · Apr 27, 2017

What carb and intake are you running? The filters never really fill so that is not a problem.

Hot unstable idle is fuel overheating along the way to the carb or in the carb itself. You need plenty of clearance between the fuel lines and any heat source like exhaust and heads. As a test you can wrap the fuel line in aluminum foil or even pipe wrap from Home Depot (that stuff burns so not too close to direct heat). If problem goes away you know the problem. If not then you may need a carb shield under the carb. I put these on every car I tune now because modern E10 gas (10% alcohol) evaporates really easy.

For a Holley or Quadrajet you can get them pre-made for a 2 Barrel you need to make your own.

https://www.summitracing.com/parts/...srese1-_-oer&gclid=CIyv-J6exdMCFcOEswodtMMMog

I bet when you shut it off engine hot with the air cleaner off you get fuel vapor coming out of the venturie (carb throats) or the vent on top of the carb. This is because the fuel is starting to boil, expands, then dribbles out into the carb throats down into the engine flooding it. When it starts I bet you get black smoke from all the fuel in the intake. Also when you start it hot loosen your gas cap to see if the tank is pressurized.

blknblu69v · Apr 27, 2017

It's an Edelbrock 600cfm with Edelbrock alum intake.
Your explanation makes sence on the hard start when hot. I ran the fuel line as far away from heat as possible. Any other suggestions to keeping carb cooler?
Tank does not build pressure.
Any ideas in the fluctuating fuel pump pressure?

Timmy390 · Apr 27, 2017

blknblu69v said:
69 Bronco, 302, new electric fuel pump/regulator, psi gauge. About 6# psi going to carb via in line fuel filter. Filter does not get over 1/3 full. When engine is hot, I get unstable idle and fuel psi drops to 2# then back up and down. Running on rear tank. Starts hard when hot and near empty filter. Could this be a clogged fuel pick up in the rear tank? Newer plastic tank installed during restoration. Hasn't ran right since, just dealt with it.
Thanks for your help!!

That sounds JUST like what I was dealing with on my 69 mach 1 390 car.

I added the biggest parabolic spacer I could (not much room under the hood) between the carb and intake which really helped but didn't cure it all.

I found my tank was not venting. As the pump took fuel out, no air was coming in to replace it thus a vacuum. The vacuum would suck the fuel out of the lines back to the tank emptying the line filter. The heat under the hood was also not helping things.

I fix the venting issue and I've not had any hot starting issues since.

Tim

blknblu69v · Apr 27, 2017

Thanks Timmy390. I think the tank is vented well. I don't get a vacuum effect when removing the cap when it's hot. I too do not have much room above the air cleaner so raising the carb might be an issue.

Cooter_76 · Apr 27, 2017

What type of line are you running to the carb? I had similar issues when I had rubber line going from the mechanical pump to the carb. Finally solved it by running hard line with a heat sheath like this: http://www.oreillyauto.com/site/c/d...+material_-1_492&keyword=heat+shield+material

jckkys · Apr 27, 2017

I'm trying to decipher the time line of changes to the fuel system that occurred after your Bronco was running well to the emergence of the current problem. Did it begin with the installation of the "newish" plastic tank, the new electric fuel pump, the new regulator, or is the weather getting hot? Most of the country is still cool while here in Tucson it's approached 100. Carburetor percolation isn't a problem in the winter. Looking at a clear filter is a waste of time. What you see is meaningless. If the tank is new, the pickup filter is probably new too. When these are clogged up they effect high output operation like climbing a grade or high speed acceleration not idling. Same for the inline filter. When and why did you install the electric pump and regulator? All I see is an idle problem. A look at the float bowls may show the slime many find after winter blend gas with 10 percent ethanol, reacts with fuel system parts. This would certainly mess up the idle circuit. A rebuild would give the carb a fresh start. If the problem goes away you know it was the carb. If it comes back then; something in the gas is messing with the carb.

PaveBronco · Apr 28, 2017

I fought the same issue for several years, even made a hard wood carb spacer and heat shied. its the Edelbrock carb, the fuel boils in the bowls and dumps down the intake, if you listen you should be able to hear it and look at the throttle blades and you'll see gas dripping on them. I finally fixed the problem with a Holley, but that had its own issues. the design of the Edelbrock does not make it a good offroad carb, the fuel bowl vents open straight into the throat and cant be extended. There are folks that run them with no issues, and I could never figure out why.

surfer-b · Apr 28, 2017

2 things I would try that would be simple

1: run it without gas cap to make sure its not a vent issue

2: makes sure the fuel lines are not collapsing from the suction of the fuel pump

blknblu69v · Apr 28, 2017

I live in Michigan and park it for the winter so I don't think it's a grade of gas issue. I did idle it without the fuel cap, reving up, and had the same reaction while on the rear tank - psi Guage would drop down to about 1-2 psi, engine idle Rpm would start to drop, psi would slowly start to rise as would rpms. The hotter the engine got, the more frequent it would happen. Shut off engine. Waite 10 minutes- hard start - like no fuel - when it does start, low psi for a few seconds.
Got my aux tank hooked back up last night. Psi was more consistent but still the same starting issue - hard start when hot.
I installed the electric fuel pump thinking it might be the cure. Waiting in drivethru line at the ice cream shop it would begin to run rough the longer I waited. One foot on brake, one foot keeping rpms up until I could get on the road. Temp gauge would only be about 190.
Don't seem to have these issues in 50 deg weather. That leave about 2 weeks in the spring and 2 weeks in the fall of no issues.

pcf_mark · Apr 28, 2017

The under carb heat should would my first stop. Nice and thin no impact to hood clearance. And insulate your fuel lines. That should do it!

jckkys · Apr 30, 2017

All these threads ignore the fact that some EB owners have this problem and many others in the same location with the same fuel system do not. One poster cured this by swapping one 2100 carb for another nearly identical 2100. When someone offers a clear understandable explanation for this I'd love to read it. Till then, what works for one may or may not work for another. I have less percolation with the AFB than 2100-2150, or Holleys. For others it may be the opposite. My stock mechanical pump with no pressure gauge or regulator works well. I have to deal with far hotter weather than Mich.

gr8scott · Apr 30, 2017

Got room for 1/2"?
https://www.summitracing.com/parts/edl-8723/overview/

Fuel supply issues

blknblu69v

Jr. Member

pcf_mark

Bronco Guru

blknblu69v

Jr. Member

Timmy390

Bronco Guru

blknblu69v

Jr. Member

Cooter_76

Sr. Member

jckkys

Bronco Guru

PaveBronco

Sr. Member

surfer-b

Bronco Guru

blknblu69v

Jr. Member

pcf_mark

Bronco Guru

jckkys

Bronco Guru

gr8scott

Bronco Guru

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