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runs bad!

Discussion in 'Mitsubishi Minicab' started by miniag, Jan 27, 2010.

  1. miniag

    miniag New Member

    I have a 91 u24t that runs bad and fouls plugs. I am on my second carb and it still has problems. It has New plugs, wires, cap, rotor and coil as well as new air filter. Acts like the choke. When warm it runs good but cold it is rough and fouls the plugs within a couple of days of use. Any thoughts???
     
  2. TRAX and HORNS

    TRAX and HORNS Well-Known Member

    Pull the air filter and watch the choke operate with a cold start. See what its doing. Might need a mirror. Its been said time and time again( I have personally seen it) that the lines coming off the top of engine that circulates fluid though carb, get clogged up. If the line are clogged up the choke wont work well. It may be clogged up in the lines or the fluid channel in carb. I recently rebuilt a Suz. carb. man it was a mess inside when I took it apart. When I unhooked the fluid lines muck came out of them. Inside of carb. was gummed up. After I finished the carb. the truck had awsome power. May not need a rebuild kit just a good cleaning.
     
  3. starpuss

    starpuss Member

    valve lash adjustment?

    also take a compression tester to it.
     
  4. miniag

    miniag New Member

    thanks

    I'll give it a try.
     
  5. Hello,
    The Key to the troubleshooting carburetors is to fisrt determine if the vehicle idles properly or not. If the vehicle idles fine and runs poorly "off idle" it will help troublshoot the fuel circuit correctly (if fuel related). Does the vehicle have AC? Does the vehicle have power steering? Is the exhaust system sputtering? Is the tailpipe pitch black? The more details you provide the easier it is for us to assist with a solution.

    Cheers,
    Don
     
  6. miniag

    miniag New Member

    Sometimes it idles good but others it idles very rough. It is good off idle for the most part. The truck has pwr steering but no ac and is a 4spd truck. At idle it smells "rich" but off idle it is clean. Thanks for your help
     
  7. TRAX and HORNS

    TRAX and HORNS Well-Known Member

    Ditto Mr. Andrews, very well said. After giving much thought and working on my share of Daihatsu's and Suzuki's I would be comfortable to say that 70 % of the trucks need a simple carb. kit installed. You dont have to be a rocket eng. to rebuild a carb.
    All of these trucks at sometime sat in a lot before the auction in Japan. They were bought and sat at another lot, then sat in a sea container, then sat a dealer for sometime here in the states or where ever. Every time they sat for 30 days are more the fuel started separating and laying a thin layer of varnish where ever the fuel was in contact. Honestly every trucks carb. should be rebuilt. And remember the choke assy. should be cleaned up when you have the carb. and check the fluid lines going to carb. and blow them out as well. This some what simple task will eliminate a lot of problems people are having with rough idle, stumble when given fuel, running rick, sticking choke ect. the list goes on. While you are at it go ahead and install a set of new plugs.
     
  8. miniag

    miniag New Member

    I contacted one importer and was informed there is not a carb "kit" available but that I could buy gaskets etc individually. Any suggestions on where to find carb parts?
     
  9. Age has a way of taking its toll on carburetors (and people..lol). On the Mitsubishi the most common problem for what you’re describing is the following

     Power Valve (It’s the plunger connected by linkage to the throttle valve) The diaphragm is very thin and becomes brittle.
     Delay Vacuum Valves (Little In-Line Mini Canisters) between vacuum ports. They delay vacuum to the chock actuator & the Fast Idle Actuator. When they fail to regulate a delay in vacuum the actuators “Bounce” or vibrate causing erratic idle. Off idle they are not utilized therefore the system will run fine off idle.
     Jet Settings. There are three Jet settings on Mitsubishi carbureted vehicles for different altitudes when produced in Japan. People are not generally aware of this. If you imported a truck that was used at a high altitude in Japan and you are at sea level you will have problems.

    About carburetor kits here in Japan. Supply for old carburetors is highly limited on old units. We do not have “Kits” per say. We look at a diagram of the carburetor and order individually each gasket “If available”. We do have rebuilt carburetors by specialty companies but expensive. A rebuilt runs about $500, and “as is” about $150. As is are usually off running vehicles but not guaranteed. A brand new carburetor from the factory (yes, some available) run from $900.

    Also remember once you take your carburetor apart there is no guarantee of replacement gaskets. You could find yourself in trouble.

    Cheers,
    Don
    www.yokohamamotors.com
     
  10. miniag

    miniag New Member

    Great info Don. Everyone has responded with good suggestions and info. I actually did buy a used carb and it is guaranteed but since it does exactly what the original one did I am thinking it is in a line, diaphragm, or other external part. I still dont think its a spark issue since I have replaced everything there - plugs, wires, cap, rotor, controle module, pickup, and coil.

    I am going to keep tinkering and see where it leads.
     
  11. fupabox

    fupabox Well-Known Member

    Valve adjustment was metioned earlier....have you adjusted them? are they adjustable on the Mits..? Don't throw any more parts at it until the free stuff has been checked;)
     
  12. miniag

    miniag New Member

    no I havent checkd the valves yet. I am not ruling anything out at this point. I have a book on that motor so I will just have to see if they are adjustable. Thanks
     
  13. miniag

    miniag New Member

    Ok, The choke is working properly, lines are cleaned, vacuum lines good. Tried 2 carbs and same result. Fuel filter new. Could fuel pump be problem?
     
  14. renchjeep

    renchjeep Member

    Maybe the fuel pump is creating too much pressure, and blowing by the needle and seat? Check your fuel pressure, unsure on the proper spec, but I think 6-9 psi would be about right for a carb. Also, maybe both carbs have the same problem--dirty/worn needle and seat. I am by no means an import carb specialist (my Mikuni is in the carb shop right now, they are trying to find parts), but I have some Holley and Rochester experience. Also, and overly lean idle condition at idle can create a "suck" factor from the venturi/float bowl on some Holley/Rochester carbs I have worked on. (Carbs are funny--sometimes they will find a way to get fuel if needed!) This may not apply to your carb, but it's worth checking. Just a matter of turning a few screws.......

    Let me know what you find. I am curious.
     
  15. renchjeep

    renchjeep Member

    I forgot to mention dirt in the fuel tank. Even with a new carb, if there is dirt in the tank, it will clog up the needle/seat and cause the same problem. Have had this problem before with my American cars/trucks. Have seen cases where the fuel tank was "lined" with a plastic type substace to prevent rusting, etc. Problem is, this "lining" eventually wears out/breaks down, and makes a gooey mess of the carb! Not pretty.
     
  16. miniag

    miniag New Member

    good thoughts. I was going to try a gauge on the fuel line to see what pressure. Tank is pretty clean and fuel is good. I'll test the fuel press and see what it is and reply back.
     
  17. There are only a few problems on a carbureted Mitsubishi that can cause the symptoms you are describing (If we are ready your comments correctly). If you have changed the carburetor twice the chances of it being a carburetor related (unless you are really unlucky) issue seems unlikely. More likely to be one of the following

    1. EGR Valve Leaking causing vacuum loss (Green Stripe on hose).
    2. Thermo Vacuum Valve (Side of the block) with a green stripe on the hose.
    3. Distributor Diaphragm
    4. Worn distributor lobe

    Use a hand vacuum pump and test each vacuum valve mentioned above. They are all static held vacuum units (they don’t bleed down automatically). The thermo switch on the block opens at 7-80 Celsius. Thermo valves can cause bad idle and since it operates the EGR valve it is an easy circuit to test. Another way to test them is simply unplug and cap them to see if the symptoms go away (unless the EGR valve is stuck open). Too much exhaust gas recirculation at low idle speeds can fool spark plugs.

    If the emission system or the distributor diaphragm is not the culprit do the timing test. Disconnect the vacuum line and plug it. Start the vehicle and let it warm up. Hook up timing light and whilst running (idle) see if there is an erratic timing movement. Run the motor up slowly and do the same. Back it down to idle. Hook up a tachometer and verify 900+-50RPM. Set timing to BTDC 5+-2 degrees. If you’re at high altitude bump it to 6-7 degrees. Confirm the basics and then go from there.

    Cheers,
    Don
     
  18. miniag

    miniag New Member

    Now were getting somewhere. It may be a couple of days but I will let you know how it is progressing. Thanks again to everybody!
     
  19. cletus

    cletus New Member

    Would the information shared in ths thread also be a good thing to check if the vehicle starts up just fine but after it gets to temperature it wont stay running? I have cleaned the carb and it did not fix the problem although I did not tear it down completely and let it soak in cleaner
     
  20. dieseldogsdad

    dieseldogsdad Member

    I just tore the carb apart and cleaned it now my truck has a very fast idle and none of the ajustments seem to slow it down. It is also going thru alot of fuel although it does not smell rich. My carb was pretty clean inside.
     
  21. BC_MMC

    BC_MMC Member

    After getting my truck back from the shop (new generic fuel pump), I noticed a lack of top end and no power. Today I filled her with premium, took it for a burn, could barely make 80 kmh, so I cracked the last can of SeaFoam, dumped it in the carb til it stalled and went to pour some in the gas tank.
    As soon as I cracked the filler cap, gas gushed out. Could this be part of my problem?
     
  22. miniag

    miniag New Member

    Thanks to everyone who offered their time and suggestions! The good news is my truck finally runs good again. It turned out to be a combination of bad vaccuum and all kinds of sediment and trash in the carburator bowl. Once I cleaned out the main jet and got the sediment out of the bowl I replaced 2 bad vacuum lines I found and she runs good again!
     

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