New engine build- stumbling under acceleration-issue found

[NHCharger]

Have about 450 miles on the engine.
440, bored .030 over stock pistons
DC cam., duration 272, overlap 48
Weiland intake
Edlebrock Thunder Series 800 CFM carb. Primary jets .113, secondary .101. Metering rods .068x.047
FireCore RTR ignition system, with the proper coil to match.

Car runs fine when I accelerate slowly, when I step on it, it bogs and hesitates/sputters. Seems to run a bit better when I have the vacuum port on the distributor plugged versus tied into the carb.
Timing is currently 13º at idle, 32-34º @ 2800.
I have played with the timing, doesn't seem to make much difference.
There is three adjustments for the plunger on the carb, tried all three did not fix the problem.
It starts fine and runs very smooth with the exception of the acceleration issue.
Thinking I might need to re-jet?? 

[68CoronetRT]

You lost me at the part where you talk about a carburetor. Sorry

Honestly though, an AFR gauge is one of the best tools to show you what's going on with your tuning. Also the base timing seems way too low. Should be like 16-18.

When you stomp on it, does it ever clear up? What happens if you just hold your foot to the floor?

I'd also try plugging up all your vacuum lines and see how it runs.

[BSB67]

How does it idle?  what is the idle vacuum? and at what rpm? Try initial at 18 or 20°.

Can be idle mix is too lean
Can be transition is too lean
Can be vacuum leak
Might need larger squirter
Might like more initial timing
Could be pump/squirter not performing correctly.

Or a little of a few of these.

[c00nhunterjoe]

Stock .030 pistons tells me they are 8:1 slugs unless you have a specific part number. Odds are it will want alot more initial like russ stated. Does this bog only happen from an idle stab? Trying rolling along in 1st gear bringing the rpm up to 2500, then stab the throttle and see what it does. If it takes off without a hitch, look at more initial timing and carb transition.

[Kern Dog]

In many cases, an off idle stumble is because the transition from idle to primary circuit is too lean. The accelerator pump shot needs to be larger to cover the rush of incoming air when the throttle is cranked open.

[NHCharger]

Made the following adjustments.
Initial timing 19* @ 850.
Vacuum is 8 @ 850.
Pump plunger on top hole-factory setting.
I sprayed carb cleaner around the base of carb. No increase in rpms.
During test drive same issues. Moved the pump plunger to bottom hole. Really no noticeable difference.
The car accelerates fine from dead stop or rolling at 20 mph up to 50-60% throttle. Once I reach the point where the other two barrels should kick in is when the stumbling and bogging starts. 
Wondering if there's some shit in the secondary jet.

[BSB67]

The car accelerates fine from dead stop or rolling at 20 mph up to 50-60% throttle. Once I reach the point where the other two barrels should kick in is when the stumbling and bogging starts. 
Wondering if there's some shit in the secondary jet.

Secondary jet issue
Air Valve to loose
Floats to low

Possibly, but less likely.  Fuel delivery - fuel pump push rod or fuel pump

[NHCharger]

I had checked for fuel delivery issue. I had a spare fuel pump which I swapped out, no difference. Fuel pump push rod-brand new. New fuel line also. Did check the fuel line to make sure it wasn't pinched anywhere.
I took the carb apart last week to check the floats, passenger side was a half inch too low- thought I had found the problem.
Looks like I will take the carb off tomorrow night and check the secondary jet.
Air valve to loose?? I'll read up on that.
Appreciate all your replies.

[torqueflite]

Fuel  pump push rod , I had that issue with my new build 383 , I listened to the internet and put in a bronze tip fuel pump rod which lasted abut 500 miles before the end wore down ,and it stopped pumping ..slowly ,,
was a prick of a thing to get out and after changing out to a standard hardened one its been all  good

[NHCharger]

Update. Pulled carb apart- again. Cleaned everything and blew out with compressed air. When I took the pump jet off there is supposed to be a pump discharge weight and discharge ball. No weight, some kind of little spring. Cannot find this spring in any of the exploded view diagrams. Bought a eddy rebuild kit and installed the weight, no spring. Car runs better under acceleration but still have hesitation and it stumbles, throttle response not very crisp compared to my 68 with a built 440 and proform carb.
Another weird thing is whenever I enter a right turn, doesn't have to be sharp the car stumbles when I initially turn right, not thru the entire corner. No problem on left hand turns.
Geuss I'll call edelbrock tech line this week.

[69wannabe]

Toss the edelbrock carb and put a good holley or proform 750 on it and it will most likely take the bog away. Put your timing around 18 to 20 initial with a total around 34 to 36 and leave the vacuum advance plugged off. I had a 650 thunder series AVS on my 383 years back and could never get the secondary bog/stumble out if it. Went to a holley 750 and never looked back at an edelbrock carb since...

[Challenger340]

just say'in....
tuning a cammed and very low compression 440(7.8:1) in front of a stock auto/Torque Converter with 3.23 gears can be a P.I.T.A.

Are the above components what you have ?

[flyinlow]

Have you looked down the carb while opening the throttle and watching the accelerator pump discharge? Good spray on both sides?

You might need a bigger pump nozzles. I think Eddy makes a set of three different sizes. The Eddy website will tell you what size pump discharge nozzle that carb comes with. Maybe there is a larger one.

I had an Edelbrock 800 and it took the largest nozzle and it was still marginal.

Hard to beat Holley accelerator pump system. Its like having two Midgets with Supper Soakers full of gasoline in you air cleaner.

[NHCharger]

Hard to beat Holley accelerator pump system. Its like having two Midgets with Supper Soakers full of gasoline in you air cleaner.

  now that's funny.
Chally340. You are correct. The 440 and tranny came out of a motor home.

[bee1971]

AVS 800 1812/1813 Series

The 800 1412/1413 has a weighted door that is not adjustable

Anyways did you try adjusting the Air Valve Door above the Secondary Throttle Plates ?

A bog tells me your air door spring is adjusted to light , opening to soon

Like BSB67 said , air valve door to loose

[bee1971]

http://www.edelbrock.com/automotive/misc/tech-center/install/1000/1812.pdf

Page 6 - Adjusting The Air Valve Secondary

[NHCharger]

Thanks Bee. I adjusted the air valve door tonight, one full turn. No difference. One night next week I'm going to swap it out with the ProForm 750 that I have on my 68 Charger and see what happens.

[flyinlow]

I like Carter AVS (Thunder) and Thermoquad  carbs. They worked well on relatively stock engines with higher vacuum. However, add a larger cam and a larger plenum unheated aluminum intake and they seam to run in to hesitation issues with sudden WOT applications. Carter (Eddy)  carbs are all mechanical secondary carbs with only one accelerator pump. They do have air valves on the secondaries to help. Holley mechanical secondary carbs are usually double pumpers.
Have a Holley 770 Street Avenger on one Charger and had a Quick Fuel 780 on the other until I went EFI. The Quick fuel required almost no adjustments to run well.

It will be interesting to see how the Pro form does.

[c00nhunterjoe]

Tuning an afb is no different then a holley in theory. Just takes time and patience. 1 saturday at the track is all it takes.

[krops cars]

Call Edlebrock. I had the same issues with a couple of carbs. The pump has I think 3 positions. If not set right it will stumble. Also I believe the you can change the metering rods. I bought a book and a kit. Edelbrock will help you with it. The kit has different metering rods and other items. Start with the accelerator pump first. If you do not get any help from Edelbrock I will look it up again for proper adjustment.

[bee1971]

Thanks Bee. I adjusted the air valve door tonight, one full turn. No difference. One night next week I'm going to swap it out with the ProForm 750 that I have on my 68 Charger and see what happens.

What Happened ?

One turn is nothing , I would have tightened it up/more resistance , three or four full turns and just see if any noticeable difference

Anyways you get the Holley installed ?

[NHCharger]

Thanks Bee. I adjusted the air valve door tonight, one full turn. No difference. One night next week I'm going to swap it out with the ProForm 750 that I have on my 68 Charger and see what happens.

What Happened ?

One turn is nothing , I would have tightened it up/more resistance , three or four full turns and just see if any noticeable difference

Anyways you get the Holley installed ?

Haven't had any time this week to work on car. I'll post an update once I get a chance to fiddle with it.

[bee1971]

"The car accelerates fine from dead stop or rolling at 20 mph up to 50-60% throttle. Once I reach the point where the other two barrels should kick in is when the stumbling and bogging starts. "

That's why I keep saying Air Door

Loosen torx screw , have screwdriver in place on spring adjustment while loosening torx screw

If you lose spring tension and Air Door goes wide open , then bring it back to the closed position by turning screwdriver counterclockwise



Turn the screwdriver clockwise until the Air Door just starts to open

Now turn the screwdriver counterclockwise about 2 full turns , in hence closing the Air Door and putting spring tension on the Air Door itself

Tighten torx screw , now tap the Air Door open with your finger and it should snap back closed under spring tension

Try it

Then next time try 3 full turns counterclockwise or 4 full turns in hence putting more spring tension/stronger on the Air Door and see if any noticeable difference ?

Have you checked any Spark Plugs for ? Color

[NHCharger]

Update. Had a respiratory virus that took a few weeks to clear so I had to lay low for a while. Also granddaughter #2 was born 
I began to wonder if this was ignition related.
Also running a Firecore RTR system in my 68 Charger so I swapped distributors a few nights ago, no difference.
I did try tightening up the air door a few more turns, no difference.
A friend had an accelerator pump from a Eddy 750 left over from a rebuild. I stuck that in the carb, ran a bit worse at low speed, no difference otherwise.
Bought a calibration kit for the carb. Swapped the metering rods and springs, no difference.
Also got that Holley from my friend that he took off his GTX. One of the mounting ears is broke off. Going to try to JB Weld it tonight and drop it on one day this week.

[c00nhunterjoe]

Congrats on the grandbaby. If you have changed every setting on the carb and not had a single change in the problem, it lays elsewhere but it sounds like you are having other issues such as the stumble in turns. Be leary on using a carb that has an ear broke off. May open a new can of worms in troubleshooting.
  I still feel the 6:1 dynamic compression ratio you are most likely working with is the main root of your problems. What octane fuel are you using? If 93, try dropping back to 87 and see if anything changes. Tak3 the proform off your other car. It is a verified known good unit. May be rich but shouldnt bog if the carb is the problem.