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Thread: Can the fuel bowls on a 4150 be reversed?

  1. #11
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    The choke horn is milled off, it's an 850 double pumper. There were 72 & 82 the engine makes 8 inches of vacuum, so I have a 3.5 power valve. The idle was lean, I had to open the screws more. The base plate says 71803. It was previously on a 350. Now it's on a 383 with 12-13:1 and large Dart heads.
    Last edited by Leon82; 06-02-2019 at 03:27 PM.

  2. #12
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    The whole idle circuit is lean, hence why you need to open the screws more.
    The idle circuit takes the engine up to the start of the main circuit.
    So if the idle feed restriction is too small, the screws will be out at 1.5 - 2 turns, versus 3/4 to 1.
    If this carb does not have screw-in air bleeds, perhaps you should think about a later more modern carb, considering the engine specs.
    I would enrich the primary to at least 75, and then possibly 84 or so on the secondary. Gary
    Regards, Gary

  3. #13
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    OK thanks. It's old, I bought it 20 years ago for my auto shop teacher and he's probably had a 20 years before that. They do not have screw in air bleeds. I'm only using it because I had it already.

    I'm going by my Auto Meter wideband A/F Ratio gauge.

  4. #14
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    Quote Originally Posted by Leon82 View Post
    Thanks, that's where I set them to. Is 1.5 turns the starting point for the idle mixture screws? It fired right up, but I have a lean spot as I open the throttle. Past 1/4 it goes up past 16.1. I used the same size power valve as the old carb. I'm thinking the jets are too small. I think they were the ones that were still in there.
    Is this 16:1 at 1/4 throttle while driving, or just free revving the engine?
    Regards, Gary

  5. #15
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    Free rev. I haven't had a chance to get it out on the road yet. It's down to like 14˝ to 15, since I opened out the screws.

  6. #16
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    A lot of variables.
    I wouldn't be worried about 16:1 on a free rev. More important about what happens while driving.
    A datalogging A/F Ratio meter with a TPS, RPM input, etc., would help. I have one, most handy. Gary
    Regards, Gary

  7. #17
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    Thanks. When I get some time, I'll take it for a spin and see what it does.

  8. #18
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    OK, so I finally got to drive it. It ran. Could the rear throttle plate position affect the idle mixture? I think I remember my teacher having me open them up on my old engine. The 650 I had before had 4 corner idle, so it probably masked the condition. The mixture screws stopped affecting the A/F ratio, so I need to fix it before I do anything else. If I had a carb with tunable air bleeds, I'd fit a smaller bleed in? When I originally put the carb on the engine was idling at 3000 RPM. I backed off the idle speed screw a good amount.
    Last edited by Leon82; 06-08-2019 at 06:07 PM.

  9. #19
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    You need to have the primary throttle blade in the correct relationship with the transfer slots, so they look like a square from the bottom.
    If the carb is the correct size for the engine, little adjustment should be necessary.
    The secondary side can be used to trim the idle speed.
    I prefer late model Holley carbs with everything adjustable. Gary
    Regards, Gary

  10. #20
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    OK maybe I should pull it off and verify. Perhaps I lowered the idle screw so much that it closed off the slot.

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