Stumble

[Geoff 2]

I am also trying to help the OP.

Carb companies like Rochester & Carter sized their carbs according to engine size, & designed their carbs so that the engine controlled the airflow it wanted....not the right foot. I am referring to devices such as air valves etc, that provided the additional air only when the engine could actually use it.
Two extreme examples of production engines that used oversize carbs...but did not bog because they had air valve carbs that added air in a controlled manner as dictated by the engine....is the Chrys Aussie 245 ci inline six & the 230 cu in 6 cyl Pontiac engine; the 245 had a 625 cfm Carter AVS & the Pontiac had an 750cfm QJ.
The Carter AFB came out in 1957 & bigger models had velocity valves in the secs to control air flow; similar operation to an air valve. Holley also got the message with it's vac sec carbs.

 

[Aron Gleason]

Uncle Tony's garage did a video awhile back on carburetor sizing. He said with a motor that's not stock. The way companies say how to determine what carburetor would work is bs. That's why you can see tunnel rammed small blocks running dominators.

 

[Geoff 2]

Yeah, right, good to know it works because Uncle Tony said so....

 

[Aron Gleason]

Yeah, right, good to know it works because Uncle Tony said so...

My carburetor guy has put dominators on many motors and they've performed flawlessly.

.

 

[1STMP]

Geoff 2,

Would you believe a 750 cfm carb
on an engine designed for 500 cfm?
No bog from cruise to WOT, does not
run rich, and from a dead stop, will
smoke 4 tires for half a block, and all
this at 4200 ft elevation?
Also know of another.
60's Camaro running dual demons
on a 350 CID. he runs the strip
regularly at an elevation of 5200 ft.
No stumble, no bog, just go.

 

[Geoff 2]

This is what I do NOT believe: that stabbing the throttle on an engine cruising at 1500, or from a standstill, with dual carbs or an excessively large single carb for THAT engine size, will not bog.
By stabbing, I mean going to WOT.

 

[Geoff 2]

I should have qualified post #146. I am talking about 4 bbl carbs where all 4 bbls go to WOT [ such as DPs ] & do not have any flow regulation of the secondary air flow.

 

[Aron Gleason]

I should have qualified post #146. I am talking about 4 bbl carbs where all 4 bbls go to WOT [ such as DPs ] & do not have any flow regulation of the secondary air flow.

Like I've mentioned before. I had a 750 double pump that stumbled. A friend who thinks he knows carburetors thinks I should get a 650 double pump. And I'm not buying into that theory.

 

[Geoff 2]

What you should get is an Edel AVS 800. No stumble, because the engine will take the air when it wants, not when you try & force it to take the air. A TQ is another good choice.

Anyway, I wish you luck with it.

 

[Aron Gleason]

What you should get is an Edel AVS 800. No stumble, because the engine will take the air when it wants, not when you try & force it to take the air. A TQ is another good choice.

Anyway, I wish you luck with it.

Thanks

 

[1STMP]

This is what I do NOT believe: that stabbing the throttle on an engine cruising at 1500, or from a standstill, with dual carbs or an excessively large single carb for THAT engine size, will not bog.

First of all Geof 2, sounds like you're
stuck on stock configurations. Every
change in the air pump'(engine)
requires a change in configuration
of the fuel delivery system.
There are literally hundreds of parts
available thru Holley that enable
the reconfiguration of their carbs
Their philosophy;
Instead of buying a new carb for
every variance, tune what

 

[Geoff 2]

I am not stuck on ANY configuration. Every configuration, stock or non stock, is not exempt from the laws of physics. Might come as a surprise but that includes Chrysler engines.
The above mentioned 440 might make peak power at 6500 rpm.....versus a stock 440 that makes peak hp at 4800 rpm.
Cruising at 1500 when the throttle is stabbed, both engines will injest the same volume of air. What will be different between the two is the density....& that affects the hp produced. Less dense, [ air is lighter ] less hp. Suddenly opening all 4 bbls on carb to WOT at a low speed on an engine where density is down is a recipe for... a stumble.

 

[1STMP]

I am not stuck on ANY configuration. Every configuration, stock or non stock, is not exempt from the laws of physics. Might come as a surprise but that includes Chrysler engines.
The above mentioned 440 might make peak power at 6500 rpm.....versus a stock 440 that makes peak hp at 4800 rpm.
Cruising at 1500 when the throttle is stabbed, both engines will injest the same volume of air. What will be different between the two is the density....& that affects the hp produced. Less dense, [ air is lighter ] less hp. Suddenly opening all 4 bbls on carb to WOT at a low speed on an engine where density is down is a recipe for... a stumble.

Get the velocity moving faster and you
get more air.
The first example was on a Jeep with
a 360 v-8. Modified air intake via the
vent on the cowl.
Second example involved two custom
built air intakes thru the front rad
support.
I had previously brought up a
requirement that the air cleaner have
a flat bottom and a generous radius
from there to the carb.
Let's give the OP a chance to catch up
where a fair diagnosis will help with
his dilemma. Changing squirters/jets/
accelerator pumps/pump cams/air
bleeds, will probably come into play.
We won't know any of the required
steps to take until there is an
honest baseline to start from.
This tuning is going to take some
time with careful consideration
at each change.
The OP has a reputable vendor
telling him his carb will work, but
I'm a bit surprised at their response
on how to fix the problem, leaving it
totally up to him to figure it out.
Hence, his call for help here.
Instead of a steadfast refusal to
work out the problems, let's work
together to get this fixed.
Thanks!

 

[Geoff 2]

Yep, get the air moving faster. Totally agree, that's a good move. Using a carb with bigger venturiis makes the air move slower. Slower air speed reduces the pressure drop across the jets so that no &/or less fuel flows....

 

[1STMP]

Yep, get the air moving faster. Totally agree, that's a good move. Using a carb with bigger venturiis makes the air move slower. Slower air speed reduces the pressure drop across the jets so that no &/or less fuel flows....

Thanks for the forward moving info.
I will say that your knowledge will
be appreciated the more we get into
fixing Arons carb problems. He's
more or less committed with what
he has.
And since his problem stems from
cruise to WOT, the first step would be
introducing more air to help
eliminating the bog.
I'm at fault in suggesting squirter
changes, but I foresee a change in
those, regardless.
I see what's going on here. To
compensate for lack of available
air, Holley suggests messing w/the
squirters instead of ways to
introduce more air into the system,
via modifying OEM induction
systems. I don't think they would ever
suggest modifying your car to get
their carbs to function at optimal.

Patience, Aron...

 

[dcala84141]

dcala84141....
Thanks for the red X.
By the way, most of that post was
quoted straight from Holley's
trouble shooting web site.
So I guess you would disagree
with them also.

dcala84141....
Thanks for the red X.
By the way, most of that post was
quoted straight from Holley's
trouble shooting web site.
So I guess you would disagree
with them also.

Sorry about that fat fingers

 

[Aron Gleason]

I took the car out today, had the black secondary pump cam and .031 squirter. Huge bog. Changed to a white cam, still a huge bog, changed to a orange cam and thought I solved the stumble, but still stumbles. I dropped squirter size from .031 to .028. Anyone have a different solution to solve the stumble issue?

 

[J5 GTX]

Could this be a fuel supply problem? You said that the stumble occurred with other carbs.
Fuel pressure too low?

I know you said it accelerates great from a standstill but, it also has time to idle, thus filling the fuel bowls ahead of the WOT event.

I have had a similar problem with a Holley 750 dbl pumper that I couldn't resolve.

 

[Aron Gleason]

Could this be a fuel supply problem? You said that the stumble occurred with other carbs.
Fuel pressure too low?

I know you said it accelerates great from a standstill but, it also has time to idle, thus filling the fuel bowls ahead of the WOT event.

I have had a similar problem with a Holley 750 dbl pumper that I couldn't resolve.

With the size of the needle and seats. I was told not to exceed 6 lbs of fuel pressure.

 

[J5 GTX]

Have you verified that you have near 6 psi? Looks like you have some kind of pressure regulator on the inner fender.

Geoff2 said that he thinks the venturi bore size is too large. Do you have a vacuum gauge on the engine?
What does the vacuum drop to on WOT?

Pardon me, if you have already answered that, this thread is 8 pages long and I'm trying to keep up.