ok guys I need to figure out why i dont have a ton of power out of my 300 wiht my 500EB carb. I Drove my buddies with a small weber 2bbl and it was a million times smoother! I cant believe it. I also cant believe that I dont have power i the upper range. I mean one day there was a very strong head wind and i could not keep 55mph in 4th. That is not gonna fly. I followed the vaccum gauge tuning on classic inline for setting the tune. I had way more power and better MPG out of my old mc2100 with 1.14v then this 500EB! What gives? no vac leaks.

 

I'm really not one to give advice, but I have been reading about powering up my 300 and I am thinking your carb is too big... I'm sure someone with actual experiance will be along shortly to tell more.

 

Okay, to start with, a 500 CFM Edelbrock carburetor is not too big. I don't know where this train of thought comes from with the 300-6 but it does annoy me to no end every time someone brings it up. Just nit-picky, you know?

The maximum size 4bbl you should run is a 600 CFM Holley. People have put 750 CFM Quadrajet's on those motors and made them run outstanding, but the Quadrajet's are variable CFM spread-bore carburetors.

Just because it's a 6, doesn't mean you can't use the same carburetors as a 8. People put 600 CFM carburetors on 302's all the time and they run amazing. So I have no doubt that with the 300 having a longer stroke than a 302, it'll run just fine with a 600 CFM carburetor. That, and many people over in the Ford Six forums and the Inline Six forums here have great performance and luck with the 600 Holleys.

In fact, one such member here on FTE called Abandoned Bronco screwed around with a 500 CFM Edelbrock on his six cylinder and he couldn't get it to run worth a flip. He switched to the 600 CFM Holley like what was on his wife's 300 Bronco, and his power went back up, and his mileage did too! I think the Edelbrock is probably sitting in his trash can.

Ford Inline Six, 200, 250, 4.9L / 300 - Ford Truck Enthusiasts Forums

That's a link to the inline-6 forum on here.

Now, to address other issues:

Do you have your float set correctly? Are you running the right size jets? What intake manifold do you have? If you have a dual plane intake, you have to orient the carburetor to where the primaries are facing the valve cover and the secondaries are going to the passenger fender. If it's a Holman Moody intake or are C-series Offenhauser or a Clifford, carburetor orientation doesn't really matter.

With the 4bbl swap you did, did you re-curve the distributor timing where you removed the EGR (NOT re-timing the motor, I'm talking about changing the springs and levers in the distributor and maybe the vacuum advance can too in order to change when the timing comes in, the total timing, when the vacuum advance comes in, etc.)? If not, your motor won't run to optimal performance.

And, the biggest thing to date:

Are you running a water heating plate on the bottom of your intake manifold?

If not, that's part of the majority of your problem.

Ford positioned the outlet on the factory exhaust manifold under the carburetor for a reason. This was so it could heat the intake and help the fuel vaporize when it gets to the bottom of the plenum of the intake. ALL intakes require heat, and on V8's this isn't an issue because the intake manifold is right in the middle of the motor. If the intake isn't heated, liquid gas will form on the bottom of the intake, and when you open up the throttle, your motor is drawing in liquid gas that won't burn as well as vapor gas will. The byproduct of this behavior is loss of power, lowered gas mileage, inability to tune your carburetor right because of the pooling gas, and bogging off idle while driving.

Also, what year is your Ford truck? Do you have the Duraspark ignition system or have you done a full Duraspark conversion?

 

i have an offy C with a stock exhaust manifold. I have not recurved the DS-II wiht new springs. Its an 82. I have not messed wiht the float, jets, rods any of that stuff on my 500. I bolted it on from out of hte box and followed the classic inline vaccum gauge tuning directions.

 

I agree with Will (1983F1503004x4) in that there are some good guys in the 6-banger forum who can probably help you. Merely changing a carburetor isn't magically going to change any vehicle into a dragster....

 

ESPECIALLY with a 300-6. A 4bbl and headers will move the power-band up a little bit, and make it a load quicker, but it still won't be "fast" by any means. Until you start getting into changing the cam and head-work, it's still a low-torque towing motor.

Now, a 4bbl and a set of header will give it LOADS more pep than what it had from the factory. You've still got to play around with it to get it right.

Alrighty, so we've narrowed down a few things.

Duraspark II ignition is very important as it is a straight electronic ignition with no computer. 1984 to 1986 had feedback carburetors and some pre-1984 California models had feedback carburetors. 80 to 83 49-state emissions vehicles are Duraspark II.

The Offenhauser C-series is a good manifold and is, I would say, the most popular. Carburetor orientation doesn't really matter with the C-series, but if it was a Dual-plane with the divided intake runners, the air and fuel flow would be uneven and could cause running problems.

Re-curving the distributor isn't priority, but it could really squeeze the last bit of power out of your current combination by letting the air/fuel mixture burn more completely and at the right time. You've got to look at what your total timing is, your initial timing, how much mechanical advance you have, how much vacuum advance you have, and when mechanical and vacuum advance decide to come in and at what RPM. There's a thread going in the Inline Six forum right now that AbandonedBronco started that you might want to keep an eye on, as well as looking on Classic Inlines and reading up about ignition timing. You can learn to do re-curves yourself, or you can take it to a performance shop or something similar near you and they should be able to do it for you.

What kind of vacuum is your motor pulling at idle? A good range for a 6 cylinder is usually 17 or 18 to 22.

You said you're still running the stock exhaust manifold, so that means that heating the intake isn't going to be a problem and it should have pretty adequate heating. However, you still won't be able to "feel" all that the 4bbl can give you unless you swap over to a set of headers or EFI exhaust manifolds and water-heat the intake.

If you have a timing light, I would set the timing on the motor at 10 degree before top dead center and see how it runs then. The 6's from our years were set from the factory at 6* and 8* BTDC. You should notice a slight improvement by dialing it back to 10*. You can also set timing with a vacuum gauge.

What gets me though, you say it's like the motor is running out of breath at highway speeds. This is definitely abnormal with a 4bbl swap.

Also, I was wrong. It wasn't the Edelbrock 500 that he was having troubles with, it was the Holley 390CFM 4bbl. I was reminded of that when I brought up his old tuning threads to get you the links for.

You might find these helpful:

https://www.ford-trucks.com/forums/1...ley-600-a.html

https://www.ford-trucks.com/forums/1...ord-300-a.html

https://www.ford-trucks.com/forums/8...ley-390-a.html

 

Not familiar with the carb your talking about but do they have a separate bowl for the secondaries?

The reason I ask is on my original holley, the secondary bowl float was stuck shut so when the secondaries opened, it just took a big gulp of air with no fuel so the engine leaned out. Went completely flat at that point as you can imagine.

 

Also, I was just re-reading my post and thinking...

Hook your vacuum gauge up to your motor, and crank the truck up until she warms up.

Then, see if scenario 14:

How to Use and Interpret a Vacuum Gauge

Occurs when you do like is described on the little interactive vacuum gauge.

You can click on the little "scenario's" listed above the gauge to make the thing animate.

You could have clogged catalytic converters. In which case, you need new ones. Some 300's came with 2, but most have 1.

Just a thought that I'd like to throw out there.

Also, did you know you can time a motor with a vacuum gauge? You won't have any idea what the actual degree it's timed at is, but you can do it.

 

Hey, Kevin. The Edelbrock 500's are reproductions of the old Carter AFB/AVS carburetors.

I don't know how many bowls they have, but I think the 500 CFM Performer has a single bowl.

 

Low torque?

 

Whoops. Long day.

I meant to say, low-rpm torque motor.

For it's size, the 300 is one heck of a pulling motor.

 

yeah i did time it with a vaccum gauge. timed the motor and tuned the carb just like classic inline says to. I had the water heat and hated it. much better wiht the exhaust heat. It will run 70 but if theres any head wind it slows down. I thought for sure it would be strong enough to maybe lose 5-8mph but not 20mph. something is not right. I'll have to look into it more and check for vaccum leaks....maybe i have a small one. today while idling it almost died and its never done that before...so i got some searching to do.