Issue with inline 250 at full throttle-Edelbrock 4 barrel

[da.slyboy]

Hi everyone, been on here awhile, just haven't posted much as most questions have been answered in the archives but am currently having and issue with my 250.

Recently rebuilt the head, and added a clifford intake with Edelbrock 1404 and Langstons headers, split out to dual exhaust. HEI unit

Currently it idles and revs nicely. Part throttle it drives and builds up speed as normal, but if I decided to stomp on it it seems to give me a little popping or lean sounding condition. I seem to lose power and have a hard time accelerating if I push too hard down on it.

Made a quick video to see if I was losing fuel pressure by stomping on it. If you forward to 2:45 mark it is the most audible of what is happening.

https://youtu.be/gN_HHNK2uyw

Just a note, ignore the flying vacuum hose at the beginning. I disconnected it because I though the can was providing too much advance (around 50 degrees WOT with connected. When the video was shot, I set the initial timing to 10 BTDC and had about a 30 degree total timing (again without any vacuum advance) I did plug the carb port.


I am stumped, at first I thought it was timing and tried multiple settings including driving it with just the mech advance and no vacuum. Then I thought it was a lean condition, but it seems my fuel is keeping up. Haven't checked to see if I have a jet clogged, but I'm mainly unsure if I should be chasing time or a fuel issue. Truck is a 4 speed (with granny) and the issue doesn't seem be a problem in the low gears. Only when in the higher more load bearing gears.

Any thoughts are appreciated.

[special-K]

I don't know anything about the carb. What CFM is it? My first thoughts are too much fuel.

[scooterpimp]

Edelbrock 1404 = 500cfm. Too much fuel / carb? Rejet? Dumping too much fuel when secondarys open ? Intake heated? Did get a laugh at that vac hose flying around. Sorry im easily amused

[geezer#99]

It's usually timing first, carb second but in this case it's carb first.
Put a fuel regulator set at 5 psi on it along with a steel tubing line.
Then put more timing in it.
Try 14 initial to start.

[RichardJ]

With stock cam and 8:1 compression, the carb with what is basically a mechanical secondary is probably too much carb. A vacuum secondary carb or the Edelbrock AVS with adjustable secondary Air Valve would probably be more suitable.

I think the secondary Air Valve on your carb is just opening way too soon, not adjustable and it's just falling on its face.

A lot of guys have claimed the Offenhauser will work better than the Clifford for an application like yours. The Clifford will flow more air, but at a loss in velocity.

I have a Carter AVS, similar to the Edelbrock AVS, on a Clifford, but with 9:1, bigger cam and more cubes.

That's a great video.

[da.slyboy]

Hmmm, I was under the impression that while the 1404 has the secondaries open mechanically it still relies on vacuum demand to pull the top air flap open and draw fuel from the bowl.

My spark plugs do show it's running a little right (black on plugs) but uncertain if that is due to a rich idle mixture.

I've combed quite a few threads of those utilizing this carb setup and none seem to demonstrate this problem. Most issues cause an initial bog or hesitation but then picks up. My issue stays persistent no matter how long I hold down the gas.

[PanelDeland]

I've never tuned a 1404 but if the throttle plate is mechanical and they are opening but the top air flap isn't getting enough vacuum to open that flap it could still be pulling fuel from the secondaries since there would be vacuum to pull fuel. Since the air isn't coming thru then it wouldn't atomize like it needs to. That would cause a "rich" condition and possible fuel pooling in the intake.

[geezer#99]

Richness at idle can be caused by having your throttle too far open at idle and uncovering the transfer slot. In that case you're idling on the power circuit. Cure is more initial timing which speeds up the idle. THen the idle can be turned back down on the carb.
If you think the secondary air valve is popping open too soon, just make a limiter for it so it won't move.

[RichardJ]

The 1404 is what they call the Performer Series. The Air Valve sits down inside, just above the secondary throttle blades. It is opened by air flow, not vacuum.

The counter weights on each end keep them closed. There is no adjustment that can be made. I've heard guys threaten to increase or change the counter weight to tailer the air valve opening, but I've never actually seen it done.

The Air Valve on the Edelbrock or Carter AVS is right on the top and is controlled by a spring. The spring can be easily wound up or relaxed to give a smooth opening without bog.
I think in this case the air valve is opening too easily and too soon.






AVS carb

[da.slyboy]

Did some experimenting this weekend and removed the manual linkage that open the secondaries and took it for a drive. I got much better results, without the issues I described. So its sounding like an over fueling issues like everyone suggested. That's a shame as I had that 1404 laying around and heard many people were having good results with it as part of the 4 barrel conversion. I guess I will use it as a glorified two barrel carb for now until I get a calibration kit and see about reducing the jet sizes further (if possible).

[Mike C]

As a general rule, popping out the intake is a lean fuel issue while backfiring or popping in the exhaust is a rich or overfueling issue.

[slomotion]

I'm coming into this a little late, but have two questions on your installation;
Is your intake a dual plane? Did you mount the carb "sideways" or facing forward?

[da.slyboy]

Originally Posted by slomotion

I'm coming into this a little late, but have two questions on your installation;
Is your intake a dual plane? Did you mount the carb "sideways" or facing forward?

Intake is a single plan with the carb sideways on the engine. The previous post seems to indicate my thoughts of it running lean when the secondaries open, since the popping sound sounds like it's coming through the intake more. Would think it would be hard for both secondaries to be clogged and not providing fuel.