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#2413203 - 12/04/17 04:22 PM Another Carb question...
Benforsp Offline
member

Registered: 07/06/05
Posts: 152
Loc: Bradenton, FL
Hey guys,

Have a BB with a moderately sized roller in it. It’s a 451 and am running a Holley 950 on it. I’ve tried a number of things but am having trouble with it back firing through the carb when I mash the throttle. Idles great revs great on the primaries but once I move to the secondaries no go. Backfired and nearly stalls the engine. I have the dizzy locked out at 37 degrees. Have tried it anywhere between 35-38 with the same result. I have 30 cc accelerator pumps. On the secondaries I’m using the brownish red pump cam with a #37 squirter. This carb ran great on a buddies BBC with similiar cubes and a big solid cam. Any help is appreciated and if you need more info please let me know. Thanks!

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#2413263 - 12/04/17 06:41 PM Re: Another Carb question... [Re: Benforsp]
Thumperdart Offline


Registered: 07/12/04
Posts: 18738
Loc: State of confusion
For starters, make sure the secondary squirter is not plugged but those need help regardless......... thumbs
_________________________
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#2413278 - 12/04/17 07:05 PM Re: Another Carb question... [Re: Benforsp]
Dave Hall Offline
top fuel

Registered: 01/21/08
Posts: 1923
Loc: Cotati, CA
Sounds like it's time for a Dom Dominator... grin

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#2413299 - 12/04/17 07:48 PM Re: Another Carb question... [Re: Dave Hall]
Thumperdart Offline


Registered: 07/12/04
Posts: 18738
Loc: State of confusion
I must say even healthy small blocks have picked as much as 5-6 mph and equal et's as long as they have gear and a good converter but that's when you know the 4150 was either not enuff or really jacked in terms of the tune............ beer
_________________________
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB for videos and lots of carb pics......760-900-3895.....

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#2413306 - 12/04/17 08:02 PM Re: Another Carb question... [Re: Benforsp]
Dragula Offline


Registered: 05/02/04
Posts: 10210
Loc: Taxes R-US, NY
ITS LEAN...under load.

I like #45 squirters in everything!
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'70 Cuda, Plan C....605 Hemi
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#2413313 - 12/04/17 08:23 PM Re: Another Carb question... [Re: Dragula]
DaveRS23 Offline
master

Registered: 01/20/03
Posts: 4647
Loc: Benton, IL.
iagree

I've also had good luck with big squirters at least in the primaries.
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#2413318 - 12/04/17 08:30 PM Re: Another Carb question... [Re: Benforsp]
RapidRobert Offline
Circle Track

Registered: 11/20/03
Posts: 33704
Loc: Lincoln Nebraska
Quote:
It’s a 451 and am running a Holley 950 on it. I’ve tried a number of things but am having trouble with it back firing through the carb when I mash the throttle. This carb ran great on a buddies BBC with similiar cubes and a big solid cam.
I'm assuming nothing was changed on the carb from him to you. at what RPM are you mashing it? vacuum leak? at the offending RPM is the carb being delivered enough fuel? A locked dist means no vac adv so no potential rotor phasing issue (near zero vac so a can loses its timing/rotor phasing shifts back CW). can you run it up to the offending RPM in your driveway & mash it & check the squirt? (fuel delivery needs would be less than a driveing mashing but it'd be a start). Keep us posted.
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#2413464 - 12/05/17 03:51 AM Re: Another Carb question... [Re: Thumperdart]
Benforsp Offline
member

Registered: 07/06/05
Posts: 152
Loc: Bradenton, FL
Originally Posted By Thumperdart
For starters, make sure the secondary squirter is not plugged but those need help regardless......... thumbs
[quote=Thumperdart]

Squirters are not clogged. I have gone from a 31 to a 37 and checked to make sure everything was clean.

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#2413465 - 12/05/17 03:53 AM Re: Another Carb question... [Re: Dragula]
Benforsp Offline
member

Registered: 07/06/05
Posts: 152
Loc: Bradenton, FL
Originally Posted By Dragula
ITS LEAN...under load.

I like #45 squirters in everything!


It has 31’s up front and 37’s in the back so you think 45’s in front and back?

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#2413467 - 12/05/17 04:30 AM Re: Another Carb question... [Re: Benforsp]
mopar dave Offline
master

Registered: 01/04/07
Posts: 5750
Loc: flint michigan
45's are huge in a 950. Shouldn't need any more than 35's. I once had 45's in a 1100 dominator on a 511 and it didn't like it. Now have 33 front and rear.

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#2413509 - 12/05/17 08:52 AM Re: Another Carb question... [Re: Benforsp]
BradH Offline
I Live Here

Registered: 01/30/03
Posts: 13776
Loc: Valhalla... eventually
What model # "950"?

What's the COMPLETE carb tune?

CR?

Cam specs?

Gear, tire, stall speed?

Launch RPM?
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#2413538 - 12/05/17 10:08 AM Re: Another Carb question... [Re: BradH]
Benforsp Offline
member

Registered: 07/06/05
Posts: 152
Loc: Bradenton, FL
Originally Posted By BradH
What model # "950"?

What's the COMPLETE carb tune?

CR?

Cam specs?

Gear, tire, stall speed?

Launch RPM?


It's a 0-82951.

The engine has 440-1 heads, CR is 11.0 to 1. Pump Gas. Mostly a street car, 4.56 gear, 275/60/15 MT tires, 3800 stall.

I haven't really driven the car much. I am just trying to get the carb to respond right then I can fine tune it, but I feel like I am too far off.

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#2413563 - 12/05/17 11:05 AM Re: Another Carb question... [Re: Benforsp]
Thumperdart Offline


Registered: 07/12/04
Posts: 18738
Loc: State of confusion
Originally Posted By Benforsp
Originally Posted By BradH
What model # "950"?

What's the COMPLETE carb tune?

CR?

Cam specs?

Gear, tire, stall speed?

Launch RPM?


It's a 0-82951.

The engine has 440-1 heads, CR is 11.0 to 1. Pump Gas. Mostly a street car, 4.56 gear, 275/60/15 MT tires, 3800 stall.

I haven't really driven the car much. I am just trying to get the carb to respond right then I can fine tune it, but I feel like I am too far off.


I did one for a BB Chevy and does not have these issues so call me and I will shoot you the tune and compare to yours if u'd like....... thumbs
_________________________
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB for videos and lots of carb pics......760-900-3895.....

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#2413746 - 12/05/17 04:15 PM Re: Another Carb question... [Re: Benforsp]
BradH Offline
I Live Here

Registered: 01/30/03
Posts: 13776
Loc: Valhalla... eventually
You still haven't given any details of the cam or the carb's current tune. That doesn't make it any easier to try and help.

The 0-82951 is the "Street HP", right? Check the actual venturi diameter and see if it's 1.38" or 1.56" I've seen conflicting specs, depending upon when the carb was made I guess. The tune would likely vary quite a bit depending upon which size it is.

I have no first-hand experience w/ the "Street HP" stuff. I'd hope that they're "flexible" enough to be tuned to work w/ your combination.


Edited by BradH (12/05/17 04:21 PM)
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#2413852 - 12/05/17 06:59 PM Re: Another Carb question... [Re: BradH]
Benforsp Offline
member

Registered: 07/06/05
Posts: 152
Loc: Bradenton, FL
Originally Posted By BradH
You still haven't given any details of the cam or the carb's current tune. That doesn't make it any easier to try and help.

The 0-82951 is the "Street HP", right? Check the actual venturi diameter and see if it's 1.38" or 1.56" I've seen conflicting specs, depending upon when the carb was made I guess. The tune would likely vary quite a bit depending upon which size it is.

I have no first-hand experience w/ the "Street HP" stuff. I'd hope that they're "flexible" enough to be tuned to work w/ your combination.


Hey BradH,
This is from the Holley site. It should be all the same with the exception of the larger rear squirter, accelerator pump change and 2.5 PV's.

I'm not with the car at this moment to know any of the air bleed sizes. What other information is needed?

Barrels
4
Booster
Down Leg
Brand
Holley
CFM
950
Choke
None
Emission Code
3
Finish
Shiny
Fuel
Gasoline
Fuel Inlet
Dual
Material
Zinc
Model
4150
Primary Main Jet
84
Primary Power Valve
6.5
Primary Pump Nozzle Size
31
Product Type
Carburetor
Secondaries
Mechanical
Secondary Main Jet
84
Secondary Pump Nozzle Size
31
Supercharged Application
No
Throttle Bore
1.750 inch
Venturii Size
1.563 inch
Part Number
0-82951

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#2413860 - 12/05/17 07:07 PM Re: Another Carb question... [Re: BradH]
Benforsp Offline
member

Registered: 07/06/05
Posts: 152
Loc: Bradenton, FL
Originally Posted By BradH
You still haven't given any details of the cam or the carb's current tune. That doesn't make it any easier to try and help.

The 0-82951 is the "Street HP", right? Check the actual venturi diameter and see if it's 1.38" or 1.56" I've seen conflicting specs, depending upon when the carb was made I guess. The tune would likely vary quite a bit depending upon which size it is.

I have no first-hand experience w/ the "Street HP" stuff. I'd hope that they're "flexible" enough to be tuned to work w/ your combination.


http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=739&sb=1

Installed straight up with 1.6 ratio rockers to bring the lift up.
Cam Detail....


Edited by Benforsp (12/05/17 07:09 PM)

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#2414161 - 12/06/17 10:28 AM Re: Another Carb question... [Re: Benforsp]
BradH Offline
I Live Here

Registered: 01/30/03
Posts: 13776
Loc: Valhalla... eventually
Hmmm...
-> 440-ish cubes with "big" heads that work better on 500+"
-> moderate CR
-> 260+ at .050" street roller
-> limited stall speed
-> street-tuned(?) carb w/ 1.56 venturi & downleg boosters
...

Starting to look to me like a mismatch of parts, of which the carb is likely one of the "What's wrong with this picture?" items, along w/ the converter being too tight. The carb may be workable, but I'll take a s.w.a.g. that the way it's set up right now is... uh... "wrong".

FWIW, the backfire upon WOT acceleration (IIRC what you posted originally correctly) would point me to verifying fuel bowl levels are high enough & accelerator pump passages & pumps are clear and working properly, and then making sure none of the air bleeds are plugged up (dirt or whatever).

My twocents (which are usually only worth about $.0125) is to tear it down completely and get (buy/borrower) the proper tools to measure all the circuits & orifices so that you KNOW what the current tune is. Post 'em, and get some feedback on what makes sense to change from there.

This is still a pretty basic carb... it can't be THAT effed up.
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#2414189 - 12/06/17 11:08 AM Re: Another Carb question... [Re: BradH]
Thumperdart Offline


Registered: 07/12/04
Posts: 18738
Loc: State of confusion
I agree w/Brad.......miss matched parts and not "ideal" however, I've modded a few of those w/excellent results and one friend picked up 500 rpm's and mph in a v-drive boat and the rest complain of traction issues........ thumbs If you're handy w/drillin n tapping I will help ya out for a cold beer............
_________________________
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB for videos and lots of carb pics......760-900-3895.....

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#2414200 - 12/06/17 11:35 AM Re: Another Carb question... [Re: BradH]
Benforsp Offline
member

Registered: 07/06/05
Posts: 152
Loc: Bradenton, FL
Originally Posted By BradH
Hmmm...
-> 440-ish cubes with "big" heads that work better on 500+"
-> moderate CR
-> 260+ at .050" street roller
-> limited stall speed
-> street-tuned(?) carb w/ 1.56 venturi & downleg boosters
...

Starting to look to me like a mismatch of parts, of which the carb is likely one of the "What's wrong with this picture?" items, along w/ the converter being too tight. The carb may be workable, but I'll take a s.w.a.g. that the way it's set up right now is... uh... "wrong".

FWIW, the backfire upon WOT acceleration (IIRC what you posted originally correctly) would point me to verifying fuel bowl levels are high enough & accelerator pump passages & pumps are clear and working properly, and then making sure none of the air bleeds are plugged up (dirt or whatever).

My twocents (which are usually only worth about $.0125) is to tear it down completely and get (buy/borrower) the proper tools to measure all the circuits & orifices so that you KNOW what the current tune is. Post 'em, and get some feedback on what makes sense to change from there.

This is still a pretty basic carb... it can't be THAT effed up.


I had the carb apart and physically went through everything. I did not go to the extent of measuring all of the orifices though...I've never actually done carbs to that point.

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#2414215 - 12/06/17 11:53 AM Re: Another Carb question... [Re: Benforsp]
Thumperdart Offline


Registered: 07/12/04
Posts: 18738
Loc: State of confusion
You have to to in order to have a base tune and to know what needs to be changed to bring it around to your cars needs...........no other way........ thumbs
_________________________
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB for videos and lots of carb pics......760-900-3895.....

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