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Ford 390 Carburetor

 
  #16  
Old 04-17-2019, 03:03 PM
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Originally Posted by Destroked 450 View Post
On engines with big cams that need a fair amount of throttle blade opening to maintain idle some have open the secondaries a little more in order to close the primaries enough to get the blade below the transfer slot.
This helped to regain curb idle adjustment.
True, and there's another hack for that: Drill a small hole in the primary blades. But I think we're way past the OP's situation.
 
  #17  
Old 04-17-2019, 03:38 PM
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Originally Posted by Destroked 450 View Post
He said it was a manual choke carb.
OP said that, but...there's no such thing! So one has to wonder what the 4V is actually from.
All 1973/79 F100/350's have an automatic choke, doesn't make any difference if it's an I-6 or V8.

1974/76 F100/350 390 available with a Holley 4V

Here's a pic of the little darlin'

 
  #18  
Old 04-18-2019, 08:11 AM
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Originally Posted by baddad457 View Post
Since when ?
Originally Posted by Krewat View Post
Since never, as far as I know. Secondary venturis have no idle circuit. If they need to be "cracked" for idle, that means the idle circuit is too rich on the primaries. Doesn't it?
Since always actually.

Secondaries do in fact have idle circuits, it is just not adjustable on the 4160's via emulsion mixture screws. Think about it -- if there was no idle/transfer circuit in the secondaries, there would be a HUGE lean spot as they started opening before the booster saw enough signal to flow any fuel.

Originally Posted by baddad457 View Post
Yea, works for me, but I would work on the idle circuit settings, not crack open the secondary's, that would only complicate setting the idle speed, possibly resulting in a "too high idle"
It is proper adjustment to crack them, and the proper setting should not make the idle too high. Since there are no emulsion screws to correspondingly close with closed throttle plates, you would be pulling in an emulsion without any additional air past the throttle and creating an overly rich idle on the secondary circuit. The secondary circuit is essentially operating as a "choke" at this point.

Originally Posted by Destroked 450 View Post
Holley does give a spec for the secondary throttle blades but I don't remember exactly what it is, primarily it cracks them open enough that the blades don't stick against the base.
On engines with big cams that need a fair amount of throttle blade opening to maintain idle some have open the secondaries a little more in order to close the primaries enough to get the blade below the transfer slot.
This helped to regain curb idle adjustment.
Originally Posted by Krewat View Post
True, and there's another hack for that: Drill a small hole in the primary blades. But I think we're way past the OP's situation.
Drilling holes in the primary blade is getting way out into the weeds for the current issue, yes. However, the cracked throttle blades are totally relevant to even a stock engine discussion.

The symptoms of them being tight closed seem to be more apparent on a worn out carb, in my experience. You can chase the adjustment around for a loooooong time with your primary idle screws and from what I can tell, it is because the secondary plates don't always "close" the same once the shafts, etc, are worn on the carb. Letting them come to rest against the screw instead of the bore makes sure that they hit the same level of closure every time.

Holley put the secondary idle screw there for a reason -- Use it. It actually simplifies adjustment, especially on a worn carb (or seems to in my experience) because now you aren't chasing varying idle conditions in the secondaries by adjusting the primaries daily.

A nice hot engine can deal with a little more tuning error than a cold one; We need to know we aren't chasing our tails on a secondary adjustment issue.
 
  #19  
Old 04-18-2019, 08:27 AM
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Secondary throttle plate workings.
 
  #20  
Old 04-18-2019, 08:36 AM
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Good info, thanks Hetz!
 
  #21  
Old 04-18-2019, 10:56 AM
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Originally Posted by NumberDummy View Post
All 1973/79 F100/350's have an automatic choke, doesn't make any difference if it's an I-6 or V8.

1974/76 F100/350 390 available with a Holley 4V

Here's a pic of the little darlin'

When I did an image search of the p/n, all I saw was electric chokes on them as well. I chalked it up to 1 of 3 things:
1. Google showing me random carburetors
2. It's already been converted
3. The OP misspoke

We'll need some confirmation on what's actually going on with that as well!
 
  #22  
Old 04-18-2019, 01:44 PM
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Originally Posted by Krewat View Post
True, and there's another hack for that: Drill a small hole in the primary blades. But I think we're way past the OP's situation.
Just don't be like this guy:


Pair of 600 Holley's I worked on(repaired) for a guy. Things that make you go "Hmmmm".
Note the heads of the screws are on the BOTTOM side of the baseplate. Yes, if they got loose, they would get eaten.
Some people should not be allowed around tools.

Once I got them both back to stock and adjusted properly, they ran like a Timex. Too many hacks don't help. It was a very mild 427 MR with 2x4's. You couldn't stand within 20ft of it at first it chugged fuel so bad. Now it's fine.
 
  #23  
Old 04-18-2019, 05:59 PM
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Originally Posted by the_hetz View Post
Since always actually.

Secondaries do in fact have idle circuits, it is just not adjustable on the 4160's via emulsion mixture screws. Think about it -- if there was no idle/transfer circuit in the secondaries, there would be a HUGE lean spot as they started opening before the booster saw enough signal to flow any fuel.



It is proper adjustment to crack them, and the proper setting should not make the idle too high. Since there are no emulsion screws to correspondingly close with closed throttle plates, you would be pulling in an emulsion without any additional air past the throttle and creating an overly rich idle on the secondary circuit. The secondary circuit is essentially operating as a "choke" at this point.





Drilling holes in the primary blade is getting way out into the weeds for the current issue, yes. However, the cracked throttle blades are totally relevant to even a stock engine discussion.

The symptoms of them being tight closed seem to be more apparent on a worn out carb, in my experience. You can chase the adjustment around for a loooooong time with your primary idle screws and from what I can tell, it is because the secondary plates don't always "close" the same once the shafts, etc, are worn on the carb. Letting them come to rest against the screw instead of the bore makes sure that they hit the same level of closure every time.

Holley put the secondary idle screw there for a reason -- Use it. It actually simplifies adjustment, especially on a worn carb (or seems to in my experience) because now you aren't chasing varying idle conditions in the secondaries by adjusting the primaries daily.

A nice hot engine can deal with a little more tuning error than a cold one; We need to know we aren't chasing our tails on a secondary adjustment issue.
You keep doing it your way, I'll stick to mine, which works too.
 
  #24  
Old 04-18-2019, 08:28 PM
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Originally Posted by baddad457 View Post
You keep doing it your way, I'll stick to mine, which works too.
Good for you.
 

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