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Old 06-06-2018, 07:33 AM   #1
applebmw
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HELP! BBC 496 Falls Flat

My 496, with new extreme energy cam, and aluminum heads, holley 750, falls on its face when I tromp it, about 3rd gear, its like the gas shut off, if I let up on throttle, it comes right back...around 4000 rpm, it revs past 4000 in 1st and 2nd, Any idea's anyone? I have Holley sniper to install, but want to be sure everything is right beforehand
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Old 06-06-2018, 09:12 AM   #2
geezer#99
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Re: HELP! BBC 496 Falls Flat

What is the cams specs?
Which Holley 750? Double pumper or vac secondary?
What’s your timing curve like?
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Old 06-06-2018, 11:57 AM   #3
GASoline71
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Re: HELP! BBC 496 Falls Flat

What fuel pump? Where is your tank located? What rig is it in? What intake manifold? Do you have a stall converter?

Gary
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Remember Murphys 2nd law of mechanical relationships... "OPPOSING COMPONENTS ATTEMPTING TO OCCUPY THE SAME SPACE, AT THE SAME TIME, GENERALLY END UP OCCUPYING ADJOINING SPACE AT THE BOTTOM OF THE OIL PAN"
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Old 06-06-2018, 01:15 PM   #4
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Re: HELP! BBC 496 Falls Flat

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What fuel pump? Where is your tank located? What rig is it in? What intake manifold? Do you have a stall converter?

Gary
1970 C-10,Stock fuel pump from 454, Edelbrock intake, tank behind seat, 2700 stall
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Old 06-06-2018, 02:38 PM   #5
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Re: HELP! BBC 496 Falls Flat

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Stock fuel pump from 454
Yeah, this is probably your issue.
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Old 06-06-2018, 02:54 PM   #6
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Re: HELP! BBC 496 Falls Flat

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Yeah, this is probably your issue.
So differ fuel pump ?
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Old 06-06-2018, 03:21 PM   #7
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Re: HELP! BBC 496 Falls Flat

Fuel delivery issue could be pump, fuel line size or a partially plugged or restrictive filter. I think you are on the right track.
Blake
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Old 06-06-2018, 04:53 PM   #8
GASoline71
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Re: HELP! BBC 496 Falls Flat

I'd say a different pump. Especially if you're gonna install a Sniper.

That 496 needs fuel!

Gary
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My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread.

The Rebuild of Creeping Death after the wreck

Quote:
Originally Posted by LONGHAIR View Post
I would never rebuild a 305.
Quote:
Originally Posted by prostreetC-10 View Post
I love using vacuum gauges as part of the carb tuning process. I hook the gauge to the inside of my garbage can and leave it there.
Quote:
Originally Posted by Marv D View Post
Remember Murphys 2nd law of mechanical relationships... "OPPOSING COMPONENTS ATTEMPTING TO OCCUPY THE SAME SPACE, AT THE SAME TIME, GENERALLY END UP OCCUPYING ADJOINING SPACE AT THE BOTTOM OF THE OIL PAN"
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Old 06-06-2018, 08:23 PM   #9
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Re: HELP! BBC 496 Falls Flat

i ran a stock pump on my 468, made aboot 550 horse. I start checking other things. But could be a weak pump...
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Old 06-07-2018, 01:01 PM   #10
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Re: HELP! BBC 496 Falls Flat

Did you buy the sniper with the required fuel pump ? Install the electric fuel pump from the sniper, install a regulator and connect it to the carb. That much closer to the sniper EFI ......
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Old 06-07-2018, 01:30 PM   #11
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Re: HELP! BBC 496 Falls Flat

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Did you buy the sniper with the required fuel pump ? Install the electric fuel pump from the sniper, install a regulator and connect it to the carb. That much closer to the sniper EFI ......
Yes but Also bought a sump because of no return line to gas tank, wanting to get running right before swapping to Sniper
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Old 06-07-2018, 02:27 PM   #12
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Re: HELP! BBC 496 Falls Flat

I was only trying to save you money on buying another stock pump. But I guess itís only money. Good luck...
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Old 06-08-2018, 07:42 AM   #13
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Re: HELP! BBC 496 Falls Flat

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I was only trying to save you money on buying another stock pump. But I guess itís only money. Good luck...
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Thanks, I have a larger pump to put on, going to install before sniper to see if its the problem, had pump ordered but did not show before setting motor back in.......
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Old 06-08-2018, 07:43 AM   #14
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Re: HELP! BBC 496 Falls Flat

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i ran a stock pump on my 468, made aboot 550 horse. I start checking other things. But could be a weak pump...
Ideas ?
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Old 06-08-2018, 09:38 AM   #15
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Re: HELP! BBC 496 Falls Flat

Check the sock in the fuel tank.
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Old 06-08-2018, 11:55 AM   #16
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Re: HELP! BBC 496 Falls Flat

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Yes but Also bought a sump because of no return line to gas tank, wanting to get running right before swapping to Sniper
I recently installed a sniper on my 85 k20 (350 Vortec) and have about 2 weeks of daily driving on it. I used the Edelbrock remote sump in the left front fender area. The setup works GREAT, especially not having to mess with the factory dual tank and return lines.
However, I've learned that " Self- tuning" regarding the Holley is very misleading. Yes it will fire up and run ok, but, if you want it to run like it came from the factory this there's alot of learning YOU have to do (or pay someone to tune, preferably on a Dyno). The tuning manual for it is 45 pages long if that gives you a hint.
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Old 06-08-2018, 01:33 PM   #17
applebmw
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Re: HELP! BBC 496 Falls Flat

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Originally Posted by SunSoaked View Post
I recently installed a sniper on my 85 k20 (350 Vortec) and have about 2 weeks of daily driving on it. I used the Edelbrock remote sump in the left front fender area. The setup works GREAT, especially not having to mess with the factory dual tank and return lines.
However, I've learned that " Self- tuning" regarding the Holley is very misleading. Yes it will fire up and run ok, but, if you want it to run like it came from the factory this there's alot of learning YOU have to do (or pay someone to tune, preferably on a Dyno). The tuning manual for it is 45 pages long if that gives you a hint.
Same set up I am going to install, does yours run better??
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Old 06-08-2018, 03:09 PM   #18
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Re: HELP! BBC 496 Falls Flat

Applebmw,
For the most part, yes. There are a few design issues that need fixed; notably the linkage. Stock, both throttle blades open simultaneously. This makes for a super stiff and extremely sensitive pedal. It's horrible if your using a standard trans! However, Holley has a $5 fix that replaces the link and allows it to be progressive (like all thier carbs). It's just a matter of swapping it out. Unlike a 4150 carb, it requires some programming changes in the unit. And of course, being electronic, it requires a firmware update for the ECU and the handheld display. I strongly suggest you start browsing the sniper forum on Holley's website. It's a wealth of information. RFI is another issue folks are having but there are easy fixes. It's nice knowing these things before you do an install and end up angry and frustrated. After all, this things $1000.00! I expect it to work as advertised. Otherwise, I'm very happy with it so far.
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Old 06-09-2018, 12:01 PM   #19
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Re: HELP! BBC 496 Falls Flat

Have you changed the fuel pump yet ?
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Old 06-09-2018, 04:46 PM   #20
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Re: HELP! BBC 496 Falls Flat

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Have you changed the fuel pump yet ?
nope, to many irons in the fire
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