Stumble

[1STMP]

Beanhead,
post #21.

I have tuned more Holleys than you have had hot dinners.

That is when/how I found out that there are better carbs out there.....& they are NOT Holleys.
My current car has four downdraft Weber carbs on it, street driven, the only one in the world that I am aware of. The only one because there was never a dedicated Weber intake made for this engine. Do you think getting those tuned is done with zero carb tuning knowledge?
As for credibility/advice, I have people thanking me publicly & via PMs for my advice.
I say it how it is [ others do not like to ] because I really do not care what people think, so get used to it.

"I have tuned more Holleys than you have had hot dinners."

Then it would stand to reason that you
should be able to get the OP's carb
spec'd to where most of the problems
are reduced, or disappear.
Very few here are gonna ditch their
Holleys for the mighty Weber.
Holley carbs have been used by ALL
of the major US manufacturers in
their performance lines. And that,
being their tunabitity. GT40's used
a Holley, as well as Shelby's Cobras.
They're not a crap carb.
Many questions have been asked
but some have not been addressed
in this post. ie...pri/sec accel pump
sizes, (have they been checked w/ a
feeler guage?) Squirter sizes, proper
assement of power vale size,
average elevation where this car is
run, etc...
The guy came here for help.
I fiddled with the Holley on a not so
numerous brand, and have managed
to tune that Holley where 4 WHEEL
burnouts are easy. But it did take lots
of "trial and error" and time to get there.

 

[Geoff 2]

Late 1980s. 383 block/440 crank. In a 71 Valiant [ ~1968 US Dart ].

48 IDF Webers

 

[1STMP]

Late 1980s. 383 block/440 crank. In a 71 Valiant [ ~1968 US Dart ].

48 IDF Webers

View attachment 1520247

So we should all ditch our Holleys and
run Webers?
Some would argue FI is the way to go.

 

[66 Sat]

Geoff you are undoubtedly knowledgeable on carburetors but your bedside manner is terrible.
1STMP is 100% correct - if you know so much why not help out instead of your incredibly boring "ditch that POS Holley" that you use every time?
You usually sing the praises of Carter AFB's but now it's Webers?
Instead of boasting about how much you know why not pitch in and help?

 

[Geoff 2]

1STMP,
Never suggested using Webers. When you work with Ws, you learn just how crude the Holley/ clones are. Performance Ws use ball brgs for the t/shafts. There were 47 different emulsion tubes available for the downdraft & sidedraft carbs. Different diameters, hole patterns & hole sizes.
Tuning these, & getting them tuned right because of the vast array of combinations of E tubes, main jets & air bleeds is a very good teaching aid on simpler carbs like Hs.

DP carbs are gimmick carbs [ & the mugs fell for them ] & you can never get them tuned to work at all rpms & at all loads. To get an engine to accept all 4 bbls going fully open on a 950 cfm carb at lower rpms without bogging will require a big pump shot & some prayers. At higher rpms the engine doesn't need the big pump shot, but still gets it anyway.
A properly designed carb like a QJ, Carter 4bbls, compensate automatically for the load & rpm; they do not deliver a huge chunk of air to the engine when you go to WOT.

 

[Geoff 2]

Yes, as long as it is the right FI. These FI kits that just fit on an intake manifold retain all the distribution/variance problems that is built into the intake. So in my opinion all you gain with these is........easier starting?
Just taking Chrys production carbs, many of the carbs had snivvies riveted to the boosters to try & fix distribution variations. None of that is fixed with the above type of FI.
Port FI doesn't fix it either. Individual runner FI does it & works. You can buy kits like this that look like W carbs but are EFI. And you can run cams that have 15-20* more duration & have a better idle than the smaller cam used with a 4bbl intake & 4bbl carb.

 

[1STMP]

1STMP,
Never suggested using Webers. When you work with Ws, you learn just how crude the Holley/ clones are. Performance Ws use ball brgs for the t/shafts. There were 47 different emulsion tubes available for the downdraft & sidedraft carbs. Different diameters, hole patterns & hole sizes.
Tuning these, & getting them tuned right because of the vast array of combinations of E tubes, main jets & air bleeds is a very good teaching aid on simpler carbs like Hs.

DP carbs are gimmick carbs [ & the mugs fell for them ] & you can never get them tuned to work at all rpms & at all loads. To get an engine to accept all 4 bbls going fully open on a 950 cfm carb at lower rpms without bogging will require a big pump shot & some prayers. At higher rpms the engine doesn't need the big pump shot, but still gets it anyway.
A properly designed carb like a QJ, Carter 4bbls, compensate automatically for the load & rpm; they do not deliver a huge chunk of air to the engine when you go to WOT.

Not trying to argue with you here.
Just running with what you stated.
Anyone that has delved into making
their hotrods run better and faster
become "comfortable" with systems
they've been most exposed to and
understand.
When it comes to performance in
today's standards, bored out 440's
with radical cams, higher compression
ratios, newer (lighter) internal/external
components, are going to rely on a
50 year old technology by running
a Rotchester? They were/are a great
carb being run under a select set of
parameters.
Just as Hollies must meet the
parameters set forth of a modified
powerplant. Edelbrocks some find
more comfortable with, as they
understand the parameters for
optimal performance from those
carbs.
Eddy"s for me, never had the "hit' I
was looking for. (all here please feel
free to flame away). To each his own.
The main point here is to help the OP
fix what he has. I doubt you'll ever
convince him to give up on what he's
got lots of time and money invested
in.
Together, we can help this guy.

 

[beanhead]

Beanhead,
post #21.

I have tuned more Holleys than you have had hot dinners.

Uh-huh yeah...so instead of being a tool every time someone brings up a Holley why don't you put all that "experience" toward helping them out...

 

[Aron Gleason]

Not trying to argue with you here.
Just running with what you stated.
Anyone that has delved into making
their hotrods run better and faster
become "comfortable" with systems
they've been most exposed to and
understand.
When it comes to performance in
today's standards, bored out 440's
with radical cams, higher compression
ratios, newer (lighter) internal/external
components, are going to rely on a
50 year old technology by running
a Rotchester? They were/are a great
carb being run under a select set of
parameters.
Just as Hollies must meet the
parameters set forth of a modified
powerplant. Edelbrocks some find
more comfortable with, as they
understand the parameters for
optimal performance from those
carbs.
Eddy"s for me, never had the "hit' I
was looking for. (all here please feel
free to flame away). To each his own.
The main point here is to help the OP
fix what he has. I doubt you'll ever
convince him to give up on what he's
got lots of time and money invested
in.
Together, we can help this guy.

Thanks. Thats why I made the post is to get some help. And like it's been said before. The 950 can be tuned to run flawless without any stumble. It does run clean and strong except for the stumble.

 

[1STMP]

Back to the task at hand...
Aron, what is the median elevation
of where your car is driven.?
(this will basically tell you what size
jets are needed).
Also, just my opinion as I'm no expert,
I'm thinking your jet size spread front
to rear is too great, and should be
closer to a 4 point spread.
What size jets were originally in the
carb? Basic rule of thumb is to drop
2 sizes for every 2000 feet of
elevation.
Holley bench tests their carbs for
sea level.

 

[blue69runner]

So, everyone is talking carbs. What fuel are you running. What fuel pump is on the car. On my 383 have a 650 Holley. It wanted to buck when I squared my jets 80 80. Primary and secondary. So ended up with 74's on primary and 76 on the metering block now it runs smooth as silk. 6.5 power valve. One change leads to another. I don't think the timing is the problem rather dialing in your carb. I have read the air holes in the secondary plates have been drilled sometimes to give you that extra air. But you say it idles fine and runs good except when you punch it then the stumble occurred. May need a stronger spring on the vacuum advance. The Holley is a simple enough carb, but it does take some thinking to get them right. My motor guy tried to sell me on like a 950 carb for my motor but knew that was way too big. Think I could get up to a 750 on it and run but very happy with my 650 I have on it now. Good luck and it is something simple I am sure you just have not hit on it as of yet.

 

[Dennis H]

850 Demon happy at sea level.

 

[Aron Gleason]

Back to the task at hand...
Aron, what is the median elevation
of where your car is driven.?
(this will basically tell you what size
jets are needed).
Also, just my opinion as I'm no expert,
I'm thinking your jet size spread front
to rear is too great, and should be
closer to a 4 point spread.
What size jets were originally in the
carb? Basic rule of thumb is to drop
2 sizes for every 2000 feet of
elevation.
Holley bench tests their carbs for
sea level.

I'm about 200ft sea level

 

[Aron Gleason]

So, everyone is talking carbs. What fuel are you running. What fuel pump is on the car. On my 383 have a 650 Holley. It wanted to buck when I squared my jets 80 80. Primary and secondary. So ended up with 74's on primary and 76 on the metering block now it runs smooth as silk. 6.5 power valve. One change leads to another. I don't think the timing is the problem rather dialing in your carb. I have read the air holes in the secondary plates have been drilled sometimes to give you that extra air. But you say it idles fine and runs good except when you punch it then the stumble occurred. May need a stronger spring on the vacuum advance. The Holley is a simple enough carb, but it does take some thinking to get them right. My motor guy tried to sell me on like a 950 carb for my motor but knew that was way too big. Think I could get up to a 750 on it and run but very happy with my 650 I have on it now. Good luck and it is something simple I am sure you just have not hit on it as of yet.

It's not a vacuum secondary carb. 950 double pump carburetor

 

[Aron Gleason]

850 Demon happy at sea level.

I've had a 850 double pump carburetor, same problem. It would stumble from cruise to wot.

 

[Aron Gleason]

Back to the task at hand...
Aron, what is the median elevation
of where your car is driven.?
(this will basically tell you what size
jets are needed).
Also, just my opinion as I'm no expert,
I'm thinking your jet size spread front
to rear is too great, and should be
closer to a 4 point spread.
What size jets were originally in the
carb? Basic rule of thumb is to drop
2 sizes for every 2000 feet of
elevation.
Holley bench tests their carbs for
sea level.

 

[Aron Gleason]

Back to the task at hand...
Aron, what is the median elevation
of where your car is driven.?
(this will basically tell you what size
jets are needed).
Also, just my opinion as I'm no expert,
I'm thinking your jet size spread front
to rear is too great, and should be
closer to a 4 point spread.
What size jets were originally in the
carb? Basic rule of thumb is to drop
2 sizes for every 2000 feet of
elevation.
Holley bench tests their carbs for
sea level.

Blp jets 80 front 94 rear which is 74/84 holley jets. Now it has 75 blp jets in front and 94 blp jets in rear. With stock jets it would stumble too.

 

[1STMP]

I'm about 200ft sea level

Then, to kinda track changes back as a
benchmark, I would set your jets to
what they were originally. I would also
change your air bleeds back to original
as well.
If the changes you've made to this
point haven't fixed the stumble, they're
not needed.
Once back to factory settings, the next
problem area to look at would be the
accelerator pumps. make sure the
Pump arm to spring clearances are
dead nuts @ (.015 ?).

 

[Aron Gleason]

Then, to kinda track changes back as a
benchmark, I would set your jets to
what they were originally. I would also
change your air bleeds back to original
as well.
If the changes you've made to this
point haven't fixed the stumble, they're
not needed.
Once back to factory settings, the next
problem area to look at would be the
accelerator pumps. make sure the
Pump arm to spring clearances are
dead nuts @ (.015 ?).

So even if horsepower picked up by dropping the primary jets, I should try going back to stock jets?

 

[1STMP]

So even if horsepower picked up by dropping the primary jets, I should try going back to stock jets?

Yes. From what I have learned by
asking many a question, jet sizes are
dependent on avaliable air not HP.
The higher the altitude, the smaller
the jet.