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TC 88 CV carb spitting gas back to filter and jets question.

Discussion in 'CV Performance' started by aaron_catrina, Apr 3, 2021.

  1. aaron_catrina

    aaron_catrina New Member

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    Hello,

    I have a '02 FXDX which I just installed a Thunderheader 2 into 1 exhaust onto as well as a Roland Sands Clarity filter which uses an exposed K&N filter. I purchased one of the premium kits and installed all the parts. (Spring, EZ screw, idle screw, etc). I used the 48 and 195 jets and have tuned the carb correctly I believe. Are these the rights jets to use for this setup? The EZ screw is sitting a little past 3 turns out if I remember right. I got to the point where the carb would backfire when I gave the bike some throttle at idle, then screwed the EZ screw back about an 1/8 turn. I noticed though that when I gave the bike a strong twist on the throttle, the carb would spit some gas into the filter. I can see the gas hit the clear widow on the air cleaner. I don't remember this happening before I installed this kit. What would cause and what would fix this??? Are the jets too big? I used the recommended jet sizes for the exhaust and air cleaner. Any help is appreciated!

    Aaron
    aaron_catrina, Apr 3, 2021
    #1
  3. kenfuzed

    kenfuzed Administrator Staff Member

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    Could be a combination of things. The jets are on the high side and you may only need a 190 with that 2-1 exhaust. Check that the needle jet (nozzle) is correctly installed and not upside down (or missing) which would cause excess fuel to spray when the needle/slide lifts. Excess fuel can also come from the accelerator pump if the diaphragm is weak or the internal check valve in the brass pump nozzle is sticking. 3+ turns on the EZ-Just is a lot for this jetting and setup which could also indicate clogged air passages.
    kenfuzed, Apr 3, 2021
    #2
  4. aaron_catrina

    aaron_catrina New Member

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    Ok. I’ve went ahead and reinstalled the 190 main jet. Would you recommend keeping the 48 jet in there as well or should I switch to the 46? I’m at 1600 ft. Anyway. I looked at the needle jet and it’s installed and done so directly. I was mistaken on the EZ-Just. After installing the 190 jet, the EZ-Just is about 2 3/4 turns out. Bikes sounds and idles good. I tuned it to where the carb would backfire then turned the EZ-Just back in until the carb no longer backfired when giving the bike throttle. The carb is still spitting fuel back out toward the filter when I give the bike a good rev. Slide isn’t stuck. Pump is good. ‍♂️
    Last edited: Apr 3, 2021
    aaron_catrina, Apr 3, 2021
    #3
  5. hotroadking

    hotroadking Super Moderator Staff Member

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    https://cv-performance.com/harley_mixture_screw_tuning

    The air cleaner assembly must be installed prior to starting the engine, not only to hold the carburetor in place but to prevent having the carburetor backfire in toward you while tuning. Start the engine as normal and bring up to operating temperature prior to fine tuning. Let the bike idle for no more than 5 minutes.

    With the engine warmed up and at idle you may now fine tune the idle mixture screw for optimal performance. Acquaint yourself with the adjustment screw location at the bottom rear of the carburetor prior to running the engine. You will need a small screw driver for adjusting the screw unless an EZ-Just has been installed. With the engine idling slow (no more than 900 rpm), turn the screw inward (clockwise) SLOWLY until the engine starts to stumble. You are working with the screw upside down so check to make sure you are turning the screw clockwise or inward. Note that not all engines will stumble or have an RPM change that is noticable when twisting in the mixture screw. This can be due to the idle jet being too large, installed cams, or ignition systems such as those on Twin Cam 88's. If unable to find the low adjustment point where the idle slows, simply set the screw at 1-3/4 turns out and proceed to the next step.

    If the engine will not idle on its own during this procedure, adjust the idle set screw on the throttle side of the carburetor until it idles correctly. Now turn the mixture screw outwards (counter-clockwise) until the engine begins to run smoothly, then add 1/8 of a turn. Maintain proper idle speed and repeat the adjustment each time you adjust the idle speed. Blip the throttle a couple of times and observe the results. If the engine responds quickly with a smooth blast and no backfiring through the carburetor, you have your idle mixture right. If a hesitation occurs then adjust the idle mixture screw out another 1/8 turn. Normally, the mixture screw should only require 2 to 3 turns out from gently seated. Anything above 4 turns indicates the pilot jet is too small.
    hotroadking, Apr 5, 2021
    #4

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