#21  
Old 08-19-2022, 05:34 PM
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Put the blue cam on it.

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Old 08-19-2022, 05:43 PM
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Originally Posted by 25stevem View Post
You should be able to fry the tires ( or at least one tire) from a idle !

If you flat out stop on it and the motor just dies with out back firing, then you have a issue(s) that are likely not carb related!
Sometimes it backfires thru the carb but not everytime

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Old 08-19-2022, 06:10 PM
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I'm guessing from the hints you've provided it's a holley style carb.

Pink cam should be just fine. I find that I use those the most out of the cam kits on many different types of applications, and install it in the #1 hole.

What I'd like to know is what holley style carb specifically, what is the jet spread front to back and what power valve are you using.
I tend to get that part dialed in first before worrying about pump shot.

From there I'd leave the pink cam and start playing with the squirter. Lots of these carbs come with pretty small .025-.028 front squirters that likely won't cover up the big hole you create whacking the throttle on a 455. But getting the front jetting correct, and a power valve that opens at the correct time helping the transition is the first thing to do. Then you might find you don't need to touch the squirter.

You're going to have to open it up and see what's inside for any of us to get you going in the right direction. Backfire through the carb when whacking the throttle is classic lean. Sometimes it's just a big hesitation. If it's doing that when free revving the engine, it's going to do it with a load too.

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Old 08-19-2022, 08:44 PM
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Formulajones, X2.

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Old 08-20-2022, 09:54 AM
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Alot of the holley carbs Ive had were small on the squirter size and would have a lean stumble if floored from a idle. Like was said .028 or so squirters probably would be too small. Usually my carbs had to have a .031 at the least. It would take 2 seconds to pull the squirters and see what size they are and try up from there.

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Old 08-20-2022, 11:14 AM
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Make sure the basics are covered. Square up the transition slot, make sure the acc pump lever is adjusted properly and proper idle mixture. Then work on your shooter size and or acc pump size.
And what carb is this???

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Old 08-20-2022, 01:00 PM
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It’s a Quick Fuel Brawler 750 mechanical secondary

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Old 08-21-2022, 09:12 AM
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There are different versions but if that's the more common street series it should have 72 front jets and a 6.5 power valve.

Since you're in the Carolinas you're near sea level. I'd like to know what vacuum your engine produces at idle to be sure, but if I had to guess you should be making 12-13 inches at idle easily enough when tuned properly.

So the power valve in my opinion opens a bit too late. I'd like to have an 8.5 in there so it's getting into the power circuit a bit sooner and helping the transition.

From there, being a 455 and at sea level, I'd also bet the 72 front jets are probably a tad lean. Considering I run that size jet in SBC's here at 5000 feet elevation, I think a 455 might be a pinch thirstier than that.

I'd likely bump that to a pair of 74's and try it. Rear jet should be 80's, I'd leave that alone for now.

Squirter should be a .031 in that carb, probably okay for the time being. Getting the power circuit working sooner may be enough to cover the big hole you're creating when whacking the throttle and you may not have to touch the squirters.

The calibration I'm seeing on that carb is more suited for a 350 out of the box, you're going to have to change some things for optimal performance and good drivability. Start with the power valve and front jet and report back.

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Old 08-21-2022, 09:29 AM
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Quote:
Originally Posted by Formulajones View Post
There are different versions but if that's the more common street series it should have 72 front jets and a 6.5 power valve.

Since you're in the Carolinas you're near sea level. I'd like to know what vacuum your engine produces at idle to be sure, but if I had to guess you should be making 12-13 inches at idle easily enough when tuned properly.

So the power valve in my opinion opens a bit too late. I'd like to have an 8.5 in there so it's getting into the power circuit a bit sooner and helping the transition.

From there, being a 455 and at sea level, I'd also bet the 72 front jets are probably a tad lean. Considering I run that size jet in SBC's here at 5000 feet elevation, I think a 455 might be a pinch thirstier than that.

I'd likely bump that to a pair of 74's and try it. Rear jet should be 80's, I'd leave that alone for now.

Squirter should be a .031 in that carb, probably okay for the time being. Getting the power circuit working sooner may be enough to cover the big hole you're creating when whacking the throttle and you may not have to touch the squirters.

The calibration I'm seeing on that carb is more suited for a 350 out of the box, you're going to have to change some things for optimal performance and good drivability. Start with the power valve and front jet and report back.
A lot of good carb advice here. The car is not a drag car with a monster camshaft and needs either a less than 5.0" power valve or 3.5" power valve.

Larger trucks with Holley cars used LARGER NUMBER POWER VALVES because they wanted ADDITIONAL FUEL to the engine SOONER, not later.

So a 10.5" Power Valve in a truck was installed for a reason.

Same deal for the recommendation to use a 8.5" Primary Power Valve in the carb. More fuel SOONER when you WOT the throttle at lower speeds.
As posted the carb is lean. 74s or even 76 jets is more common on 455 sized engines on the Primary side.

It would be nice to have the actual "List # off the airhorn of the carb and the build date code.

Tom V.

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  #30  
Old 08-21-2022, 11:04 AM
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First thing I would like to know from the OP is what the transition slot looks like? This could be the cause of the dead spot..no amount of jet changes or PV changes will help if this isn't correct. Cover the basics first.

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  #31  
Old 08-21-2022, 12:10 PM
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Default Dead Spot At Idle

What ignition system are you running on your engine? If you are running a vacuum advance HEI distributor you may be having an intermittent open in the pickup coil when vacuum immediately drops when the throttle is opened. Also, along the same condition you may have a ground wire problem with the point plate if you are running a point style distributor. If you are running a vacuum advance style distributor, disconnect and plug the vacuum line and see if your condition decreases. Also make sure that your initial timing is adjusted. I would recommend 10 to 12 degrees advance as a starting point.

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Old 08-21-2022, 03:11 PM
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I am in the Carolina mountains. Way above sea level. My transition slots are not uncovered, in fact the idle screw is barely turned in. My idle is a loping idle between 900-1100. I am using the Summit RTR distributor that I stepped down to the 18 degree bushing in to cure the overheating. Now it stays dead between 176-183. Initial is 14 degrees. 15 pounds of vacuum.

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Old 08-21-2022, 03:59 PM
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If I am reading you right and your saying that your primary throttle blades are barely open, then that is a good part of your issue.
This means you must be idling more off of the secondary’s then the primary’s.
Can you pull the carb off and post up a picture of how your primary throttle blades look in relation to the transfer slots in the base plate?
PS.
Vacuum is stated in inch’s, not lbs.

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Old 08-21-2022, 06:19 PM
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The Transfer Slot position should be exposing about a .040" square window below the throttle blades on the Primary Side of the carb.

Post up what you think the amount of Transfer Slot exposure should be in your OPINION on the Primary side of the carb.

Tom V.

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  #35  
Old 08-21-2022, 07:36 PM
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Originally Posted by 64speed View Post
I am in the Carolina mountains. Way above sea level. My transition slots are not uncovered, in fact the idle screw is barely turned in. My idle is a loping idle between 900-1100. I am using the Summit RTR distributor that I stepped down to the 18 degree bushing in to cure the overheating. Now it stays dead between 176-183. Initial is 14 degrees. 15 pounds of vacuum.
That's plenty of vacuum. Step up the power valve. 6.5 is way too low for that engine. Start with an 8.5 and work from there.

I'd bump up the front jets too. 2 sizes to start, but as mentioned, it might take 3 or 4 sizes.

This will most likely take care of your WOT stumble.

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Old 08-21-2022, 07:57 PM
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I will post some pictures as soon as I’m able. It’s not idling on the secondaries. Maybe “barely” was the wrong word. I can adjust it easily with the throttle screw it just isn’t turned in but about 1 to 1 1/2 turns

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Old 08-28-2022, 05:19 PM
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I will post some pictures as soon as I’m able. It’s not idling on the secondaries. Maybe “barely” was the wrong word. I can adjust it easily with the throttle screw it just isn’t turned in but about 1 to 1 1/2 turns
Mikes Reply:
Good info. learned a lot about Holly Carbs, as far as my Tri-Powers are concerned on my 428 ci, I need to ease into the accelerator, "not" stomping on the accelerator as your explaining, you don't want to spin the tires any way on acceleration or you lose traction. My Carbs work as they are designed, if you want motorcycle response get Webbers or SU carbs or so I have learned. IMO, this does not mean you can't tweak in your Holly Carb. better though! GOOD LUCK.

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Old 08-28-2022, 07:35 PM
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Mikes Reply:
Good info. learned a lot about Holly Carbs, as far as my Tri-Powers are concerned on my 428 ci, I need to ease into the accelerator, "not" stomping on the accelerator as your explaining, you don't want to spin the tires any way on acceleration or you lose traction. My Carbs work as they are designed, if you want motorcycle response get Webbers or SU carbs or so I have learned. IMO, this does not mean you can't tweak in your Holly Carb. better though! GOOD LUCK.
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I found this today, might help in your case, good Luck.
https://help.summitracing.com/app/an...4730/related/1

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