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U42t Cv40 carburetor swap

Discussion in 'Mitsubishi Minicab' started by Bowe, Dec 3, 2022.

  1. Bowe

    Bowe Member

    This isn’t really a tutorial but more me wanting to get more documentation out for this swap. Some of it will be trial and error I imagine. I’m currently in the process of swapping a Keihin Cv40 off a Harley sportster into my Minicab. I’m using the adaptor kit from desert_machine on eBay.

    With a little bit of modification the stock air intake, throttle cable, and fuel pump can be used.
    Some people have teed the fuel supply line after the pump into the return line to retain the factory pump. That’s simpler and has the same result as what I did. A Kawasaki mule pump can also be used, it’s the proper pressure already and self regulating do return line can be abandoned. I chose to install a wix 33040 filter with a return port after the factory pump. A regulator and gauge goes between pump and carb, the end result in my case should be any pressure over 2psi being sent to return. This does create an issue of the system being double filtered but I’m okay with that. The red supply from pump loops back into wix filter but changes hose color from 1/4 to 5/16 line. Ignore the Bluetooth hoseclamps. 2AAA322B-1FA7-4AEE-A425-E3CA3E5D76A1.jpeg

    The adaptor kit comes with a new knock and end for the stock cable and instructions of how to cut adjuster off stock cable, I chose instead to modify the throttle holder on the carb. I like to be able to return to stock whenever I do something like this. EBC48A0B-F142-4AFE-B41C-7CAD70696659.jpeg

    The stock intake assembly is much too long to fit with the cv40 so the boot that attaches air box to carb needs cut down slighly on both ends. The coupler that attaches carb to intake manifold also needs cut down as much as possible while still keeping carb from touching manifold and transferring heat. Even with these cuts made it’s a tight fit, but it does fit. 13EF2815-61C7-4D4C-B240-499D96FB166B.jpeg

    I coupled the coolant hoses that were connected to carb with a 3/8 barb fitting. I believe they can also be blocked off with no issues.

    I installed a wideband O2 sensor to aid in tuning as I’m no carb wizard and I already had it from an old build. I’m at 1000’ elevation and I’m running a 42 for slow jet with a good idle speed and a/f close to 14.7. My wideband is being flaky so I can’t get wot a/f but through trial and error I settled on a 155 main. Would probably run a 170+ main if using a pod filter. Ended up combining parts from Harley style choke cable and cable from Honda Foreman 400. Think I’d prefer a snowmobile style that can be left partially on without holding it. E2AEE292-7E33-40A5-8285-3DADB832D5CF.jpeg 4CB35D2F-3329-4753-937F-30D4136B4270.jpeg 5AA29E44-A1B9-4068-BCA6-CEAD7E62D111.jpeg

    For vacuum lines I knew I needed to retain 4wd vacuum and brake booster vacuum which is easy because it’s pulled directly off manifold as well as keeping vacuum advance, that’s easy enough to trace from carb to distributor. Aside from that I capped everything else off and am deleting it as I clean engine bay up. I already blocked off egr due to the passage way being clogged so that eliminates one line.

    The only issue I have with this carb is the choke/enrichment circuit. With the choke pulled it idles up slightly but is clearly too rich and not getting enough air. It’s certainly driveable but for cold weather I want a higher idle speed without doing anything other than pulling choke. After digging into this I see that the starter jet is not supposed to be removed changed etc. It appears to be ~45 jet which is larger than my slow jet, I’m thinking of buying a 35 or 40 starter jet made for a different Keihin and threading the hole the existing starter jet is pressed into. The hole is ~4.5mm and the new jet would be 4.8mm so in theory it should work. Ill test it on my Chinese cv40 before the real one.

    It appears a Rhino 660 carb may have a starter jet that can be changed out? That feature and the fact it has an additional carb heater to aid in cold weather operation would probably make me choose that carb if I did it again.

    Attached Files:

    Last edited: Feb 26, 2023
  2. mark gerdes

    mark gerdes New Member

    do you have a 4g82 ? did you keep your factory carb? im trying to make the factory mikuni run right . its not easy. i bought the rebuild kit from china . helped some but now its worse again. i think its a vacuum problem. wont pull fuel into engine. wont idle. also it will only start with the air intake hose unlatched from the air filter, even though no restriction from the airbox. weird problem. thanks. mark
  3. Bowe

    Bowe Member

    Mine has the 3g83, I quickly lost patience with the factory carb. Replacement parts for them are mostly expensive but poor quality or really expensive for good quality.
  4. mark gerdes

    mark gerdes New Member

    i took my factory carb apart again for the 10th time. finally found the idle circuit and cleaned it out again, runs lots better and idles. i still have an airbox restriction. even with a new filter still boggs down, with it removed it runs like a race car. still working on that.
  5. Bowe

    Bowe Member

    C99F06E3-1796-4481-A190-118FD9892A20.jpeg 727D6436-EBA4-4F50-BBF0-5BDB479F8082.jpeg We’ve been using the heck out of the kei truck and it’s working awesome. I think im about as close to the factory carb as one can get without a water controlled choke and ability to have a high cold idle with enrichment on.

    I believe I remedied the lack of a high cold idle with enrichment on. My choke/enrichment was functioning correctly it was just too much fuel. I reasoned it would be easier to reduce the amount of fuel than add air on that circuit. I restricted the pressed in jet with a small strand of copper wire and used the truck during the winter to test. That worked well so I removed the pressed in jet and threaded the hole for a Dellorto 5mm jet. Threads are 5mm x .75. I need to wait for cold weather to see what jet I need in there. Have a 35 currently.

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