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Old 12-31-2018, 07:22 PM
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Holley carb stumble

I put a new Holley carb 80457sa, 4160 600 cfm on my new truck motor.
I ran my truck with my old edelbrock for a couple weeks before i bought this Holley.
I runs great at idle, no stumble, quick throtle response. But when I'm driving and get on it, it will stumble for a split second and take off.
My accelerator pump is adjusted right, the fuel bowls are on the money.
I cam with a .031 squirter and I have tried .028 and .035. No changes.
My motor is a 357, 9.85 compression
221/221 @.5 470/470 lift. Lsa108
Dart 8ron eagle heads.
It's in a 69 c10, that's why I tried a smaller squirter, I read that a heavier vehicle might
need a smaller one.
I have not tried pump cam yet, I would have to order them.
Also... My air fuel mixture at idle has the highest vacuum with only . 75 turns out.
Everything I have read says to start at 1.5 turns out. My motor doesnt seem to like that?
Timing 16 I inital, 36 all in @3000 rpm
I do use vac advance too.
Thanks

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Old 12-31-2018, 07:46 PM
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The "1-1/2 turns" rule is just for new and rebuilt carbs as a basic rich enough setting to get it up and running on the engine, so that you can then final tune it to the application...rarely ever will they remain at the 1-1/2 turns out setting once tuned in. It has been misrepeated so many times folks don't know the reason for it anymore, and just think it is where they should end up when tuned in....rarely will it be so.

As far as tuning for best vacuum, this is the likely cause of the stumble you have, it is not the best setting for any kind of performance engine with a bigger than stock cam.

Bigger cam higher performance engines typically like to be 1/8 to 1/4 turn out richer from best vacuum setting, in order to cover the reversion that comes from longer duration and the later closing intake valve. Because it is so lean at idle, and off idle and cruise speeds it also runs off the idle and transition circuits that the too lean setting is likely causing the stumble.

Richen it up a bit and test drive it. You may have to tweak the idle speed screw when you richen the mixture screws, to get back up to your idle speed, but that is normal.
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Old 12-31-2018, 09:55 PM
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That's a vacuum carb, more than likely the secondaries are dumping open just a tad to quickly when you get on it from a cruise rpm. Try going up one step on the vacuum canister spring to a heavier one. OR you can install an adjustable canister (or make one yourself) that will allow you to find tune the secondaries.
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Old 12-31-2018, 11:26 PM
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Quote:
Originally Posted by chasracer View Post
That's a vacuum carb, more than likely the secondaries are dumping open just a tad to quickly when you get on it from a cruise rpm. Try going up one step on the vacuum canister spring to a heavier one. OR you can install an adjustable canister (or make one yourself) that will allow you to find tune the secondaries.
The 80457's all have the Black secondary spring, stiffest one made, so I'm guessing this isn't the issue.
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Old 01-01-2019, 05:20 AM
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Why did you change carbs in the first place?
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Old 01-01-2019, 07:11 AM
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Quote:
Originally Posted by ericnova72 View Post
The 80457's all have the Black secondary spring, stiffest one made, so I'm guessing this isn't the issue.

Then in his case he might need to clip the stock spring slightly to increase the stiffness or again move to an adjustable one. I would certainly try increasing the idle mixture first slightly as most rodders fail to understand that while cruising you can be running on the idle circuit mostly and his transition from idle circuit to main circuit could be slightly lean however whenever I hear that it's bogging or has a kind of lag hit when getting on it suddenly, it is almost always a fuel shot coverage issue. But he already mentioned that he bumped up the shooter but if the shooter cam was delayed in the throttle cycle it might not have been enough or as effective as one might hope. I love Holley type carbs - they're so damned tune-able it's crazy but you have to work at it.
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Old 01-01-2019, 07:50 AM
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Quote:
Originally Posted by 55 Tony View Post
Why did you change carbs in the first place?
When I had my new motor dynod I had my edelbrock on. My machinist told me that a Holley would add 20 to 30 horse. So we slapped a Holley on it that wasn't tuned for my motor and we made another pull. It added 25 horse. Made me a believer.
It also made a huge difference in my truck.
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Old 01-01-2019, 08:12 AM
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Quote:
Originally Posted by Sawlog View Post
When I had my new motor dynod I had my edelbrock on. My machinist told me that a Holley would add 20 to 30 horse. So we slapped a Holley on it that wasn't tuned for my motor and we made another pull. It added 25 horse. Made me a believer.
It also made a huge difference in my truck.
Dyno operators can make any number that you want to see come up. Playing with the numbers is nothing new. IF there truly was that much difference there was something radically wrong with the Ede. A mere Ede to box Holley swap will not get you 25 HP. Reapir or retune the Ede and you'll be within a couple of ponies.
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Old 01-01-2019, 08:59 AM
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He had no reson to play with the numbers, he does not sell carbs.
I have know this guy for over 20 years.
He has been building pulling truck, circle track and old and mew muscle car motors for years.
I trust in his experience.
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Old 01-01-2019, 09:08 AM
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What Power Valve is in it? JMHO, might want to try a lower number PV.
JMHO, a properly tuned Edelbrock carb will get just as much HP.
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Old 01-01-2019, 09:32 AM
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Quote:
Originally Posted by 36 sedan View Post
What Power Valve is in it? JMHO, might want to try a lower number PV.
JMHO, a properly tuned Edelbrock carb will get just as much HP.



Yup
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Old 01-01-2019, 10:12 AM
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I know those carbs like the back of my hand and it should have come with a silver spring and an orange pump cam and I also would move your idle mixture screws out to 1 full turn and see how it goes and does then. Your cam with my experience is right at the radical edge for that idle circuit calibration out of the box being on the lean side. I won't say anything yet on what might be done for that part as you need to try a few other things first.

I run that exact carb now with some upgrades and modifications on my dart 377 shp build and when tuned and calibrated right they are nice running carbs. I swapped out to a rear metering block and center hung fuel bowls and a quick fuel primary metering block and a bigger 1 11/16 base plate to make it a 650 plus installed down leg boosters.

Try the mixture screw adjustment with one full turn and see how it does. Also are you running you vacuum advance on timed port or full manifold? That can make a difference as well but mostly at idle and off idle.
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Old 01-01-2019, 10:52 AM
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Quote:
Originally Posted by eric32 View Post
I know those carbs like the back of my hand and it should have come with a silver spring and an orange pump cam and I also would move your idle mixture screws out to 1 full turn and see how it goes and does then. Your cam with my experience is right at the radical edge for that idle circuit calibration out of the box being on the lean side. I won't say anything yet on what might be done for that part as you need to try a few other things first.

I run that exact carb now with some upgrades and modifications on my dart 377 shp build and when tuned and calibrated right they are nice running carbs. I swapped out to a rear metering block and center hung fuel bowls and a quick fuel primary metering block and a bigger 1 11/16 base plate to make it a 650 plus installed down leg boosters.

Try the mixture screw adjustment with one full turn and see how it does. Also are you running you vacuum advance on timed port or full manifold? That can make a difference as well but mostly at idle and off idle.
Full manifold
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Old 01-01-2019, 01:22 PM
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Quote:
Originally Posted by Sawlog View Post
When I had my new motor dynod I had my edelbrock on. My machinist told me that a Holley would add 20 to 30 horse. So we slapped a Holley on it that wasn't tuned for my motor and we made another pull. It added 25 horse. Made me a believer.
It also made a huge difference in my truck.
I'd say if the slapped on Holley simply added 25 horses over the Edelbrock without tuning it certainly was better tuned to your engine than the Edlebrock this is not just a case of any Holley being pulled off the shelf will do that. This, also, is missing the knowledge of what CFM differences, if any, exist between these two carbs. Your engine configuration will easily respond to a higher flow carburetor like a 750 Holley or 800 Edelbrock.

Bogie
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Old 01-01-2019, 07:49 PM
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Quote:
Originally Posted by ericnova72 View Post
The "1-1/2 turns" rule is just for new and rebuilt carbs as a basic rich enough setting to get it up and running on the engine, so that you can then final tune it to the application...rarely ever will they remain at the 1-1/2 turns out setting once tuned in. It has been misrepeated so many times folks don't know the reason for it anymore, and just think it is where they should end up when tuned in....rarely will it be so.

As far as tuning for best vacuum, this is the likely cause of the stumble you have, it is not the best setting for any kind of performance engine with a bigger than stock cam.

Bigger cam higher performance engines typically like to be 1/8 to 1/4 turn out richer from best vacuum setting, in order to cover the reversion that comes from longer duration and the later closing intake valve. Because it is so lean at idle, and off idle and cruise speeds it also runs off the idle and transition circuits that the too lean setting is likely causing the stumble.

Richen it up a bit and test drive it. You may have to tweak the idle speed screw when you richen the mixture screws, to get back up to your idle speed, but that is normal.
I tried that today, it made matters a lot worse. I also took the secondary linkage off to make sure they were not trying to open too soon. No difference.
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