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Thread: 850 DP 2 corner idle question

  1. #1

    Default 850 DP 2 corner idle question

    Hey guys, I have an older 850 DP mechanical secondaries with 2 corner idle. I had a lean spot at about 2000-2500 rpm if I just ease into the throttle shown by a wideband. So I took out the primary metering block and tapped the idle feed restrictors for 6-32 brass hex heads then drilled holes with wire gauge bits. I started with a .038 and it was way lean I had to have the idle screws out 5 full turns just to run. Then went to 0.61 and it was way to rich 12.2-12.5 on the wideband at idle. Now I'm waiting for some new bits to come in the mail in between the .038 and the .061 sizes. Can anyone tell me the stock size of the press in IFR in the primary side? Carb number 4781. I have been doing some research and all I hear is stock is about .035 or so but I think that is for 4 corner idle. Why do my IFRs seem so large?

  2. #2
    Join Date
    Jan 2013
    Location
    Constantine, MI
    Posts
    148

    Default

    normally .028-in. to .035-in. in diameter

  3. #3
    Join Date
    Jan 2013
    Location
    Constantine, MI
    Posts
    148

    Default

    Changes of .001-inch, say .030- to .031- inch represents an area (and flow) increase of 7%. Equation: Area = Pi [r2]. Hope this helps.

  4. #4

    Default

    Well I took it all apart and cleaned everything good, put the .038 IFR back in and it did the trick richened it up at idle, I then put a .061 idle air bleed in but it is still a little rich. I have the idle screws only 3/4 of a turn with the transfer slot .030. So now I set the transfer slot to .020 and will be putting a .055 idle air bleed in as soon as ups arrives with my wire gauge bits today. I hope this will allow me to richen it it some so I can set the idle at 950. I hope this helps my lean spot also that I have between 2000-2500 rpm.

  5. #5

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    I squared the carb with 80 jets, have .038 IFR, and have .055 IAB in now. The stumble is gone real smooth, but it is pig rich!! I mean when I mash the gas the AFR goes to 11.8. Light cruise is still in the 12.5-12.8 range, I did get the idle at 14.0-14.9. Also when I close the hood with or without an air filter the rpm drops by about 2-300 rpm. I have a scoop in the hood and there is about 3 inches between the carb and top of the hood. Why is the rpm dropping? Also what do you guys think I should do to get the whole RPM range leaner now?

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