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 33Likes
06-04-2024, 11:57 AM
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Half-Ass Member
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Join Date: Jun 2005
Cobra Make, Engine: ERA #732, 428FE (447 CID), TKO600, Solid Flat Tappet Cam, Tons of Aluminum
Posts: 22,025
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Not Ranked
Google some pics of your carb so you know exactly what you're looking for. There's a pretty big vacuum tube towards the rear that is for the brake booster. Maybe you have that hooked up to your PCV. If that was just unplugged and completely open it would be a monster vacuum leak. Then you're going to have a smaller vacuum tube, mine is on the front base of the carb slightly towards the passenger side. When I put a vacuum gauge on it I have to use a tool, I can't do it with my fat fingers. Then there will be another tube, maybe on the primary metering block. Once you get the hang of looking for them they'll jump right out at you.
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06-04-2024, 12:45 PM
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CC Member
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Join Date: Nov 2007
Location: Clayton,
IN
Cobra Make, Engine: ERA 838
Posts: 1,146
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Not Ranked
Some of the High Performance 850-950 Holley style carbs have NO vacuum fittings.
I suspect the shop that worked on it may have changed some carb settings or jets/bleeds.
If the timing is right - roughly 16 degrees at idle and 34-36 degrees at 3000 RPMs, I would bet for lean condition.
I would go thru the Holley dial in procedure step by step.
John
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06-04-2024, 01:43 PM
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CC Member
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Join Date: Jan 2022
Cobra Make, Engine:
Posts: 161
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Not Ranked
Quote:
Originally Posted by Grubby
Some of the High Performance 850-950 Holley style carbs have NO vacuum fittings.
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John - thanks for the tip here. As I would like to avoid pulling the carb if at all possible.
Here is a pic of the underside of my carb that I pulled from the Holley website.
Problem is that I have no idea whether this pic depicts any vacuum fittings  |
06-04-2024, 01:54 PM
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CC Member
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Join Date: Nov 2007
Location: Clayton,
IN
Cobra Make, Engine: ERA 838
Posts: 1,146
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Not Ranked
No vacuum connections in the carb shown in the photo.
John
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06-04-2024, 02:00 PM
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Senior Club Cobra Member
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Join Date: Jul 2000
Location: Chilliwack,BC,
BC
Cobra Make, Engine: F5 Roadster
Posts: 1,422
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Not Ranked
Msd
hi,
Do you have an msd ignition box? if so that's the signs of it failing.
Perry 
__________________
F5 cobra Mark 4 roadster, **SOLD** Ruby Wine Red with pearl,
dual 2" roll bars, warmed up 302, Edelbrock AVS carb and heads, E Street aluminum Heads, Comp cam and roller rockers, AOD, 4.10 Eaton Posi, Power Baer/disc brakes, block hugger headers, 2 1/2" under car exhaust, F500 18" black spoke wheels.
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06-04-2024, 04:19 PM
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CC Member
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Join Date: Jan 2022
Cobra Make, Engine:
Posts: 161
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Not Ranked
Quote:
Originally Posted by HighPlainsDrifter
hi,
Do you have an msd ignition box? if so that's the signs of it failing.
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Perry - my immediate answer was no. But then I went and crawled around the car once more to confirm. No ignition box under the hood - that much for sure. But thinking that maybe it might be on the other side of the firewall, i did find a box tucked up under the dash in the passenger footwell. But for the life of me, I could not find any markings on it. Hard enough to even snap a clear pic of it.... |
06-04-2024, 04:35 PM
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CC Member
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Join Date: Nov 2009
Location: Edmond,
Ok
Cobra Make, Engine: Classic Roadsters
Posts: 631
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Not Ranked
Street Fire, a MSD product
__________________
 Chaney Shores Studio
Last edited by sunman; 06-04-2024 at 04:38 PM..
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06-04-2024, 02:09 PM
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CC Member
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Join Date: Jan 2022
Cobra Make, Engine:
Posts: 161
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Not Ranked
Quote:
Originally Posted by Grubby
No vacuum connections in the carb shown in the photo.
John
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i was hoping you would say that! |
06-04-2024, 01:54 PM
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Half-Ass Member
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Join Date: Jun 2005
Cobra Make, Engine: ERA #732, 428FE (447 CID), TKO600, Solid Flat Tappet Cam, Tons of Aluminum
Posts: 22,025
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Not Ranked
What's the exact model number for your carb?
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06-04-2024, 02:12 PM
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CC Member
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Join Date: Jan 2022
Cobra Make, Engine:
Posts: 161
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Quote:
Originally Posted by patrickt
What's the exact model number for your carb?
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80805-1
Date code: 1177
My deciphering from the Holley website, the above info for my carb translates to “950CFM ULTRA XP CARBURETOR”
https://www.holley.com/products/fuel...rts/0-80805HBX
Date code translates to 117th day of 2017, or 27 April 2017 |
06-04-2024, 02:40 PM
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CC Member
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Join Date: Nov 2009
Location: Edmond,
Ok
Cobra Make, Engine: Classic Roadsters
Posts: 631
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Not Ranked
MSD problem
Backfiring thru the carb is an ignition issue
__________________
Chaney Shores Studio
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06-04-2024, 02:41 PM
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Half-Ass Member
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Join Date: Jun 2005
Cobra Make, Engine: ERA #732, 428FE (447 CID), TKO600, Solid Flat Tappet Cam, Tons of Aluminum
Posts: 22,025
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Not Ranked
That's a pretty fancy carb. But a Holley is still a Holley and cracking open your secondaries is just the old school way to do it when you don't have an integrated idle bypass valve, which you have. 98% of all Holley drivability problems are the primaries not being set properly on the transition slot, the idle mixtures being off, the floats being off and the change in under hood temperatures that makes the air thinner in a car like your Cobra.
But, we could be completely wrong and you really have a bad spark problem. Maybe the MSD box, the coil, the pickup, who knows. The absolutely correct way to approach your problem would be to swap a known-to-be-wonderful Holley 750 Vac Secondary from someone's car at the local Cobra club on to your car and see if all of sudden the problems were gone. Is that a possibility in your case? It doesn't even have to be a Cobra club, an old Ford or Mustang club would do just fine.
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06-04-2024, 05:28 PM
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CC Member
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Join Date: Jan 2022
Cobra Make, Engine:
Posts: 161
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Quote:
Originally Posted by patrickt
...The absolutely correct way to approach your problem would be to swap a known-to-be-wonderful Holley 750 Vac Secondary from someone's car at the local Cobra club on to your car and see if all of sudden the problems were gone. Is that a possibility in your case? It doesn't even have to be a Cobra club, an old Ford or Mustang club would do just fine.
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The closest member of the New England Cobra Club I know is almost 200 miles away. Unfortunately...
I went to my local Cars & Coffee and asked around about local shops etc. And everyone pointed me back to the same shop that I tried last year. And they didnt seem to have much carb expertise. Unfortunately.
I have a buddy that knows how to use his timing light. When he is available, we can check the timing.
In the meantime, I will follow the Holley tuning instructions for the rebuilt carb. |
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