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Point me in right direction for motor upgrades


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  • Point me in right direction for motor upgrades

    Hi! I would like any advice in hopping up my 89 YJ with the 4.2 I-6. I just got done with a tune up,plugs,wires,cap&rotor,replaced valve cover gasket,oil sender and thermostat. It has 101,000 miles on it and is all stock. I fixed all the oil leaks and replaced air filter, seems to have a stumble around 1000 to 1300 RPMs. Is this a trait of the carb?
    Start out with what you think are the best bang for the buck, and /or should I look for a FI 4.0 six before throwing $$$ at a 100,000 mile engine?
    Thanks for any and all advice, Steve.
    Last edited by MN YJ; 06-29-05, 08:38 PM. Reason: spelling

  • #2
    i've heard good things about swapping the FI and head (and intake manifold/exhaust header) from a 4.0 onto your 4.2 block. no personal experience however.


    • #3
      not too familiar with carbs...but from my exerience it sounds like it. Check the fuel pressure and the filter.

      if you want to upgrade just fix the one you have and buy a newer 4.0 that needs rebuilt...rebuild it to how you want it then swap it...minimal down time. IF you dont get any answers here then visit and post it up there...i know there are people that have done the conversion and might be able to help you out. good luck
      87' XJ "Gnarly"

      To some ! it's a six-pack, to me it's a Support Group. Salvation in a can!
      ~ Dave Howell


      • #4
        Id rebuild yours and put the Mopar performance multi-port fuel injection kit on it. comes with every thing computer,fuel lines, distributar, fuel pump, wireharness, the kits got it all and its well worth it. then i'd put on a header. the coast of the kit is around $2600.00 but the power increse is incredable. my budy did it to his 87 xj and that thing just blow the doors off my 99 xj when we raced.


        • #5
          For the cost of that Mopar kit and just a bit more, you can have a stroker. I wouldn't spend a dime on a carbureted engine unless you are simply resigned to accepting it as a perpetual PITA. The Carter carb is junk, you have to fiddle with it endlessly until you find some settings that work. Go up a hill and the mixture changes...

          I went through my 4.2L and warmed it up with a cam, mild port and polish, 5 angle valve job, etc, and I've been kicking myself ever since. It's not that it doesn't have lots more power - it does. But it still has a carb. If you are even remotely considering driving it in off camber situations, don't bother with the carb. It's a pain. I considered the 4.0L head swap, but after you buy a conversion wiring harness (not required, but makes it easy), there are only a few other things to consider to simply do the whole 4.0L swap. Find a donor junkyard engine and rebuild it. While you have the engine at the machine shop, you might as well take them a 4.2L crank instead of the 4.0L crank, and get yourself a set of pistons made (or a stroker kit), and make some real power.

          I'll eventually document my costs in doing this, but I bet that it will end up at just over $3000, including donor engine. Not bad compared to the MPFI kit considering I'll have 300 ft-lb of torque. Ask cbremer.
          1986 CJ-7; 4.6L stroker, balanced & blueprinted; 5" lift, 35x1250 MTRs, Poison Spyder Full Width kit,
          My Jeep

          Moab Rocker Knocker Video:shades: