Thread: Help to get off the line please!

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First post here, please bare with me !

So I built one of the 7 engines in the article "7 Hot Engine Combos - Mild to Wild" from Chevy High Performance magazine August 2003, I think it was the Muzak Mouse but I do not recall, specs of my build are as follows:
-350 SBC, 4 bolt mains, 9:1 compression
-Cam is an SSI from PAW: 214/224 duration (280/290 adv) with .443/.465 lift @50
-GM Cast Iron Vortec Heads
-Edelbrock Performer RPM Air Gap Intake
-GM Ram's Horns manifolds, 2-1/2" (clearance issue or I would have gone with headers)
-600 CFM Carb (mine is a Carter AFB)

Engine runs GREAT! It is in my '59 Chevy 1/2 Ton pickup with a Turbo350 trans and a 10 bolt corporate wtih 3.42 gears. I believe my torque converter stall is around 2100-2400 but the trans was a freebie so I didn't ask too many questions at the time!

Part throttle and WOT performance are awesome but transitioning from idle to the primary circuit is an issue. I have called and worked with Edelbrock Tech Support but alas, no avail.

Engine has 18 in of vacuum idling in park between 800-850 RPM and drops to 600-650 RPM in gear, not too much lope either; it takes off smooth with minimal throttle. Distributor is stock HEI with 20 degree weights and stock springs, for now, vacuum hose disconnected, for now (possibly forever), I am all in with 36 degrees of advance around 2800 RPM (16 degrees initial timing).

PROBLEM is, truck cannot get off the line... It bogs or stalls if you floor it.

I would appreciate any insight or advice from the experts out there or anyone that has a similar build; I know this combo will work, I just have not coaxed the genie out of the bottle yet. Thanks in advance

Welcome to CHR. Sounds like you've got a great combination on the engine build. Cam spec are reasonable as are your gears and stall speed (I really like the Vortec heads) and your vacuum is pretty good as well.

My first thought is that you you may be rich on the primary jets/metering. The Edelbrocks are a bit rich out of the box and if you had a 1406, I would point you to their (Edelbrock's) web site for the instructions on how to diagnose and then replace the jets/metering rods. I'm assuming that you have a true "AFB".

While I suspect that your Carter may be a jet size bigger than it needs to be, a quick check can confirm. If you have a good shop near by, they can sniff the exhaust and tell you if that's the problem. I'd try that first.

Others will chime in, I'm sure.

Again welcome to CHR,
Glenn

Transition circuit is a step or two fat... As Glen said, most are fat out of the box... If you don't have the Edelbrock calibration kit, you'll need to get it then follow the chart in the book (or on the Edelbrock site) to get the carb dialed in... Once you get the calibration right on the carb, you may want to reconnect the vacuum to the ported side of the carb, then work on the vacuum canister to slow down the advance rate a bit.....

Originally Posted by glennsexton

My first thought is that you you may be rich on the primary jets/metering. The Edelbrocks are a bit rich out of the box and if you had a 1406, I would point you to their (Edelbrock's) web site for the instructions on how to diagnose and then replace the jets/metering rods. I'm assuming that you have a true "AFB".

Good info... I have both Carter and Edelbrock manuals, which look suspiciously identical, I guess I should get the Tuning Kit that has the assortment of rods and jets. Yes my Carter is a true AFB

While I suspect that your Carter may be a jet size bigger than it needs to be, a quick check can confirm. If you have a good shop near by, they can sniff the exhaust and tell you if that's the problem. I'd try that first.

Not sure if any local shops have smog sniffing setups for hotrodders, most all focus on smog here is for registration and environmental - or are you suggesting a dyno shop?

Originally Posted by Dave Severson

Transition circuit is a step or two fat... As Glen said, most are fat out of the box... If you don't have the Edelbrock calibration kit, you'll need to get it then follow the chart in the book (or on the Edelbrock site) to get the carb dialed in... Once you get the calibration right on the carb, you may want to reconnect the vacuum to the ported side of the carb, then work on the vacuum canister to slow down the advance rate a bit.....

I have gone over the chart, don't really understand it yet, and have called Edelbrock tech spt, they pointed me towards step up springs and accel pump rod holes - I tried ALL they suggested and have not seen any significant improvement at all.

From what you two gentlemen are suggesting I might want to change metering rods to one with a smaller rich-step and/or go to a leaner main jet - did I get that right?

Thanks to both Glenn and Dave

Originally Posted by Dave Severson

Transition circuit is a step or two fat... As Glen said, most are fat out of the box... If you don't have the Edelbrock calibration kit, you'll need to get it then follow the chart in the book (or on the Edelbrock site) to get the carb dialed in... Once you get the calibration right on the carb, you may want to reconnect the vacuum to the ported side of the carb, then work on the vacuum canister to slow down the advance rate a bit.....

The cam you have was used by G.M for 20 years in 305s and 350 and is a
easy to live with but has been best described as a "LAZY" Cam.
My Engineer recalibrated it and set it up with another 4* advance on
top of the Comp cams grind and that made a difference down low but cost
a bit on top as expected..Later I swapped it for a 222/222..450/460 GM
cam which is a mild cam & increased the Rear wheel torque by 155 lbs max.
My 355" had 195 TFS heads and 10.1/1 comp with 1.5/8 headers into a
2.5" system after collectors. Holley 600 with 6lbs fuel pressure+ 38* Total
advance. [10* static.] All the best with the project

Originally Posted by skyeking

The cam you have was used by G.M for 20 years in 305s and 350 and is a easy to live with but has been best described as a "LAZY" Cam.

Interesting, I would love to know the notorious history of this "lazy" grind...

My Engineer recalibrated it and set it up with another 4* advance on top of the Comp cams grind and that made a difference down low but cost a bit on top as expected

This is the beauty of this hobby, unlimited options and opportunities to play!

Thanks for your repy

sorry I disagree I think the transition circuit is too lean because the float level is too low when the throttle plate opens and uncovers the the trasition port the manifold vacuum drops rapidly and the the t port relies mostly on ventures pressure difference to flow fuel called Bernelle's law especially at w.o.t. just my opinion I could be wrong .....ted

Originally Posted by glennsexton

My first thought is that you you may be rich on the primary jets/metering. The Edelbrocks are a bit rich out of the box and if you had a 1406, I would point you to their (Edelbrock's) web site for the instructions on how to diagnose and then replace the jets/metering rods. I'm assuming that you have a true "AFB".

While I suspect that your Carter may be a jet size bigger than it needs to be, a quick check can confirm. If you have a good shop near by, they can sniff the exhaust and tell you if that's the problem. I'd try that first

All good info... I have both Carter and Edelbrock manuals, which look suspiciously identical, I guess I should get the Tuning Kit that has the assortment of rods and jets. Yes my Carter is a true AFB

Originally Posted by Dave Severson

Transition circuit is a step or two fat... As Glen said, most are fat out of the box... If you don't have the Edelbrock calibration kit, you'll need to get it then follow the chart in the book (or on the Edelbrock site) to get the carb dialed in... Once you get the calibration right on the carb, you may want to reconnect the vacuum to the ported side of the carb, then work on the vacuum canister to slow down the advance rate a bit.....

I have gone over the chart, don't really understand it yet, and have called Edelbrock tech spt, they pointed me towards step up springs and accel pump rod holes - I tried ALL they suggested and have not seen any significant improvement at all.

From what you two gentlemen are suggesting I might want to change metering rods to one with a smaller rich-step and/or go to a leaner main jet - did I get that right?

Originally Posted by ted dehaan

sorry I disagree I think the transition circuit is too lean because the float level is too low when the throttle plate opens and uncovers the the trasition port the manifold vacuum drops rapidly and the the t port relies mostly on ventures pressure difference to flow fuel called Bernelle's law especially at w.o.t. just my opinion I could be wrong .....ted

Just for argument sake, based on my very finite understanding of carburetion, would we be able to diagnose too lean/too rich at transition by how the engine reacts to flooring the pedal? For instance, too lean and the RPM would increase and stall due to fuel starvation vs. too rich the engine would flood and bog and possibly stall. Just thinking out loud here...

I can and will check/set float levels when I inspect/change jets, but am not sure this is part of the problem, no fuel starvation at WOT so far, but I haven't check fuel pressure yet either...

Thanks to Ted, Glenn and Dave!

Well – sorta:

While it seems complex, the carburetor consists of a “barrel” (or a series of “barrels) that provide a means of ambient air to pass through a venturi in route to the intake manifold. The venturi narrows in section and then opens again, causing the airflow to increase in speed in its narrowest part. The throttle butterfly rotates in a manner that ranges from nearly no restriction (WOT) to nearly closed (idle) controlling the flow of air through the carburetor throat and thus the quantity of air/fuel mixture delivered, which regulates engine speed.

Fuel is introduced into the air stream through small holes at the narrowest part of the venturi. Fuel flow is in response to a particular pressure drop in the venturi and is adjusted by means of calibrated openings in the fuel path typically called jets.

When the throttle butterfly begins to open (from the fully closed position), it exposes additional fuel delivery holes where there is a low pressure area created by the butterfly blocking air flow; these allow more fuel to flow as well as compensating for the reduced vacuum that occurs when the throttle is opened, enabling the transition to metering fuel flow through the regular open throttle circuit.

As the throttle continues to open, the manifold vacuum drops (since there is less restriction on the airflow), reducing the flow through the idle and off-idle circuits. This is where the venturi shape of the carburetor throat comes into play, due to Bernoulli's principle (i.e., as the velocity increases, pressure falls). The venturi raises the air velocity, creating high speed and thus low pressure, sucking fuel into the air stream through a nozzle or nozzles located in the center of the venturi. Sometime carburetors use booster venturis (annular discharge) within the primary venturi to increase the effect.

When the throttle is closed, the airflow through the venturi drops to a pressure that cannot maintain this fuel flow, and the idle circuit takes over.

Bernoulli's principle, which is a function of fluid velocity, has a dominant effect for large openings and large flow rates. Since fluid flow at small scales and low speeds is dominated by viscosity, Bernoulli's principle is ineffective at idle or slow running. The idle and slow running jets are typically placed after the throttle valve where the pressure is reduced partly by viscous drag, rather than by Bernoulli's principle.

My two cents worth - excerpted from some old archives rattling around my brain. Hope it helps.

Regards All,
Glenn

Great info Glenn

In reading the manual (carb prinicpals) as well as your post it seems richening up the primaries may not be the fix for me, I am looking at the secondary metering calibration since the transition seems to be handled by both the secondary aux system as well as the pump system - perhaps why Edelbrock suggested moving to the longer accelerator pump stroke to deliver more fuel.

Edelbrock's tuning sheet for the 1405 carb (very similar to my AFB) suggests upgrading secondary main jet which is located in the float bowl so perhaps I can kill two birds at once when I go checking/setting float levels...

Do one adjustment at a time. As suggested it could be the float level. Under hard acceleration, the fuel could move to the back of the bowl and cause the bog. I little more fuel in the bowl could fix it. If you do more than one adjustment at time you run the risk of not knowing what the problem was.

Originally Posted by Mikej

Do one adjustment at a time. As suggested it could be the float level. Under hard acceleration, the fuel could move to the back of the bowl and cause the bog. I little more fuel in the bowl could fix it. If you do more than one adjustment at time you run the risk of not knowing what the problem was.

Not too sure it is a fuel issue, my problem happens when standing still and flooring the pedal, the truck just bogs and will stall if you stay on it. Anything you ask it to do over 1500 RPM happens without hesitation.

The really vexing part of this is 1 out of 20 times the truck WILL launch, I just haven't figured out what is different between when she does and when she doesn't - which is why I am looking at the carb first - of course 4.11 gears couldn't hurt but let's not go there

How much part could operating temperature play? My cooling system is apparently SUPER efficient with an electric fan and aluminum radiator, engine runs around 160 all the time unless I turn the fan off...

Thanks Mikej!
BTW that is a sweet ride you've got there

Summit has sensor, bung and guage for less than $100. I just ordered them for my flathead...just wondering which exhaust to put bung in or can I do both with another bung and sensor?

Originally Posted by Ford Guy

Summit has sensor, bung and guage for less than $100. I just ordered them for my flathead...just wondering which exhaust to put bung in or can I do both with another bung and sensor?

The bung is usually installed close to the collector, mark the spot where the sensor will fit and be able to be installed and removed in-car (that's kinda important) and drill/weld the bung in.

There are other gauges out there that are dual and run 2 sensors, one on each side, but are more around $300 price range for some reason.

Honestly, once it is set up I wouldn't think you need it, just one more gauge to glutter up the dash and distract you, but it is nice to have