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Thread: Vacuum port identifier

  1. #1

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    Vacuum port identifier

    Need help identifying what & where this vacuum port should be routed to. The port seems to have both pressure & vacuum (bi-directional). It's located between the depression chamber port & the auxiliary acceleration pump port. I have attached a pic.
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  2. #2


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    Scroll down to the manuals section, check in on the 216+ manuals camoit posted. unless someone has memorized the Vacuum routing for the 2.6 :-)

  3. #3

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    I checked out the manuals section but still couldn't find anything regarding this port...which I think is called the "air jet nipple". Thanks for ur reply LSR Mike. Maybe someone will actually take a look @ their carb/port and report back....

  4. #4



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    If I'm corect then this should describe what you are pointing at and where it conects. It should have a small preformed bent hose between the two.


    Mikuni Carburetor - Secondary Throttle Valve Fix

    The 4 cylinder 2.6L Mitsubishi engine (as seen on the Montero/Raider) is fed by a Mikuni carburetor. The Mikuni carburetor is a two-barrel design, which has a mechanically operated primary throttle and a vacuum actuated secondary throttle. When you press on the gas pedal, you are only opening the primary throttle valve. Vacuum formed in the primary throttle body by air passing through operates on a diaphragm actuator (called the "depression chamber" by Mitsubishi) which opens the secondary throttle in proportion to how much vacuum is formed, thus how widely the primary is opened. In many older 2.6L engines, the actuator for the vacuum secondary loses integrity and will no longer hold a vacuum. This limits or prevents the opening of the secondary throttle, and your truck ends up with a one-barrel carburetor!
    The primary throttle is fairly easily found and accessed on the side of the carburetor. The vacuum actuator is a little harder. (The following is from my ’87 and I understand that ‘87-’89 are interchangeable, while ’86 and earlier are slightly different in size and appearance.) The actuator is a rounded, sort of UFO-shaped device with a coiled spring protruding from the bottom, and a vacuum hose/fitting on the top. It’s located around the back of the carburetor, and the spring should be connected close to the primary throttle.

    Do I Have a Problem?
    The primary symptom of a failed secondary throttle actuator is loss of power, especially at wide open throttle (WOT). If your Montero/Raider has trouble with hills, passing Yugos or other strenuous full throttle activities, check your secondary!

    Okay, I Have a Problem...Is It My Secondary Throttle Actuator?
    With the engine OFF you should be able to easily open the primary throttle by hand. With the primary throttle held open, you should be able to easily open the secondary as well. Note that there is a mechanical interlock which should prevent the secondary from opening when the primary is not open. If you cannot manually operate the secondary then you may have a problem beyond the scope of this article. If your secondary opens easily, remove the vacuum hose and attach your vacuum pump/gauge to the actuator fitting. A "good" actuator will hold vacuum, while a "bad" actuator will not. My actuator was so far gone that I couldn’t even draw a vacuum, let alone hold it!

    Okay, my secondary throttle actuator is bad, now what? (The Procedure)
    First, acquire a replacement. The Mitsubishi dealer CAN order this part separate from the carburetor, although they probably have no idea what the heck you're talking about at first. The key words are "depression chamber". This is what the factory shop manual calls the device that I call the secondary throttle vacuum actuator. Once I spoke those magic words, my dealer said "Son of a #$@!&, here it is..." while looking at his parts diagram for the carburetor area. FWIW, the Mitsubishi part # for my '87 is MD612713, which was *ONLY* $96.29 special order from Japan, then tossed in a bottle into the ocean with my name on it… I politely declined! I believe that this part is interchangeable between 1987-1989 models. It definitely appears that my 1987 is compatible with a 1988. I called around various junkers and found a fella with an '88 2.6L who'd look for the part for me. We found it right on the back of the carburetor (duh!) and a quick check with my vacuum pump showed it holding! (Also, movement of the spring was clearly visible - maybe .5" to 1" of travel or so?) Despite a long lecture from the junker on how you "can't buy this separate from the carburetor, which is $600" I escaped for only $25. The junker had to use an impact driver to loosen the two screws holding the actuator to the carburetor…remember this later!
    Second, remove your old actuator. When I tried to pull my actuator, I too was unable to loosen the screws with the carburetor attached to the engine. Since the Mikuni is warmed by engine coolant, attempting to remove it will normally result in antifreeze going EVERYWHERE. I drained about a gallon of antifreeze out of the radiator, and was able to remove the carburetor without pouring antifreeze into the intake manifold. (Note: my truck was on a reasonably steep driveway facing nose-down, so I can't swear 1gal is enough on level.) For peace of mind, I also stuffed a clean rag into the opening left by the carburetor, so I was 100% sure no loose pieces/gunk ended up in the engine! With one person holding the carburetor, and one wielding a plain Phillips screwdriver, a friend and I were able to remove the actuator without incident. The end of the actuator is a coiled spring which attaches to the secondary throttle arm with a TINY C-clip - DON'T LOSE THIS CLIP!!!!
    Finally, attach the new actuator. Simply hook the coiled spring back over the secondary throttle arm and reattach the C-clip that you hopefully didn’t lose in step 2. If you had to pull the carburetor off in step 2, reattach same and dump your antifreeze back into the radiator! Fire up your truck and enjoy 2-barrel power once again.

    Click image for larger version. 

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    Last edited by camoit; 01-29-2012 at 02:43 PM.
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  5. #5

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    Camoit its actually the nipple next to the 1 for the secondary dashpot. My secondary is connected correctly. There is a gas like vapor coming from this nipple and well eat thru any vacuum line within a week. This nipple is midway @ the bottom of the passenger side of the carb. I have noticed that not all carbs have this nipple. I have a 88' 2.6L Power Ram 50, 4x4, stick shift.

  6. #6



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    There is also the ASV Air Switching Valve. and the CAV Coasting Air Valve.
    But the location, angle and size looks like it's for controlling the purge valve of the charcoal canister. Is there anything on your truck that is not hooked up?
    If you take a peace of copper wire and strip the insulation off of it. Then take 1 strand of the wire and stick it in the tube, where does it come out at? above the butterfly or under the butterfly. If above how far open does the butterfly need to be before it lines up with the throttle plate? 1/4 throttle, 1/2 or what?
    Where did you come up with that picture?
    Last edited by camoit; 01-29-2012 at 05:46 PM.
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  7. #7

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    This is how my purge control valve is connected. There is a couple of nipples on the drivers side of the carb that's been caped off, I've tried these before w/no luck. I'll try the wire procedure and update. The pic. of the carb is from a friend who once owned a truck identical to mine, this is a carb he ordered some yrs. ago. He had no clue where the vacuums go as he didn't installed the new carb.
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  8. #8



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    So it's a new carb you have, never installed? Many times there is a hose routing diagram under the hood. It's possible it's not the correct carb for your engine type. What is your engine number? If you look in the Wiki under history it will help you nail down what you have or should have. We have seen so many mix and match trucks and parts you would be surprised.
    You said a fuel vapor. Is there any liquid fuel coming out of it?
    What happens if you just plug it?

    Does this help?
    Click here for direct link. Then save it on your computer and you can Zoom in on things and read it.

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    Last edited by camoit; 03-30-2012 at 09:56 PM.
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  9. #9

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    No mine is the original carb. that was the pic. of my friends carb. he had ordered for his truck. I've tried plugging it...it either blows off or eats thru the hose. No it's not in liquid form but a moist vapor. A quick look @ ur diagram...I don't see anything, but I'll take a closer look.

  10. #10



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    Do you need to SMOG it? If not you could always pinch it closed and solder it up. It's a little permanent but it would stop it from blowing off. It's just an idea.
    I'm searching for some information that may help you. So some of the things I toss up here may not be correct for your truck. But when I find it and drop it on here I bet you will spot it right away.
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  11. #11

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    Don't want to solder it close. What I have done is used a fuel line (2') on it vs. a vacuum line and put a screw in the other end which allows the vapor to bleed off keeping pressure down so it want just blow the hose off the nipple. Just to note with nothing on this nipple, it pretty loud & gets louder with more throttle thus increasing the blow off.

  12. #12



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    That does not make any sense, There should not be that much pressure from a carb.

    What does it sound like?
    What engine model number is in your truck?

    Also take a look in here under emission. Grab the zip file one and see if there is any information that may be for your truck. http://www.mightyram50.net/vbulletin...=7008#post7008
    Last edited by camoit; 01-30-2012 at 01:28 AM.
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  13. #13

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    I guess it could be an exhaust leak; it just looked like fuel varnish that gets on the carb. directly above that nipple.

    Now it does sound more like an exhaust leak…somewhat like that of an exhaust leak around a header/manifold.

    My engine is the G54B w/KM145

    I checked out the zip file, didn’t really see anything helpful w/regards to this issue.

  14. #14



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    Ya I put up the wrong one. try this one chapter 6 It covers just about everything you have.
    http://www.onsiteconcrete.net/d-50/F...-1983-1993.zip
    Some carbs had a secondary egr in the carb.

    I'm starting to think it's the wrong carb. Or it was superseded by the one you have on it. I would guess it's exhaust and it should be OK to solder up. Electrical solder should be fine.

    How larg a hose is on it?
    Last edited by camoit; 01-30-2012 at 01:59 PM.
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  15. #15

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    I checked out that link yesterday, my carb. doesn’t have the sub egr inside the carb.
    This is the original carb that came on the truck when it was new.

    I think it’s a 1/8”hose on it.

    If I solder it up…then where is that exhaust going to go? Will that create more issue?

    Could I route it using a “T” into the PCV hose ?

  16. #16



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    That sounds like a tie in to the egr port, but it shouldn't pressurize like that - check to see if the egr is working and the port from the head to the intake is clear. If the egr is clogged, it may be using that port to find a way to escape. try bypassing the egr vacuum hoses so the egr valve stays closed and see if the pressure goes away.
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  17. #17

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    The EGR valve has been removed, cleaned and check…it’s operating correctly. Connecting ports are clean/clear.

    The EGR valve remains in the closed position (as it should) when the engine starts and at idles. It’s operated off “ported” vacuum, vacuum that is supplied only when the throttle is cracked open.

    So yes there is still pressure at this port when the egr valve is closed.

  18. #18



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    can you get us a picture of the carb on the truck?
    Do you know if the manifold has been swapped out for some reason? If so it's possible that some one put on an early model.
    OR there is a possibility that 1 jet valve is is burnt and allowing gas back to the carb.
    I also contacted http://www.recarbco.com/ Real nice guys down there. It was surprising to here how helpful they are. I just need to call them back after 10Am and they should have an answer on what is going on, and where it goes. They deal with these things all the time. I'll also see if they can come up with the different part numbers for the carbs we use and a copy of the exploded views or a rebuild procedure manual. I did ask how much they sell them for just for GP. They have them for about $400 with a 1 year warranty set on an engine and tested. Not that you need to replace it. One thing he did say is there are variations between the trucks and mini vans. I'll find out more tomorrow.
    Last edited by camoit; 01-31-2012 at 02:14 PM.
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  19. #19

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    No, everything on this truck is original, no parts swapped.

    Jet Valve? That’s interesting…because a guy was listening to my truck earlier today & he said that it sounded like I had a bad “jet valve”. He indicated he once owned 1 of these trucks, that developed issues with the jet valves. He said he took them out, removed the springs, cut them down short enough so they wouldn’t be activated by the rocker arm, welded-up the newly cut open ends and reinstalled.

    He also said with my trucking running like this, it's loosing lots of vacuum thus running lean.

    If this is my problem…should I do this or get the Jet Valve Elimination Kit?

  20. #20



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    I'm sorry I totally spaced calling them back. They will call me back tomorrow. The guy he needs to talk to only comes in in the AM, he is like the Oracle in the movie The Matrix, but the carb world. I'm at 87.6% in thinking it's the jet valve causing this issue. You can tell the bad one. It will be hitting the rocker and no way to put a .006 feeler gage in there. Put in a Jet Valve Elimination Kit and be done with them things. I never had a failure with them just cracked heads, blown gaskets and tranys that would pop out of gear.

    Can you put a vacuum gage on the manifold vacuum and tell us what it's pulling at an idle. Also how steady the needle is. If it whips back and forth it's going to be in the valve train or jet valve.
    Last edited by camoit; 02-01-2012 at 05:55 PM.
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  21. #21

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    I don't have a vacuum gauge, I'll see if I can barrow one. I up loaded a video of what it's doing...http://youtu.be/53_hfRanvNA

  22. #22

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    Here is a pic. the red arrow indicates the problem nipple, the blue arrow indicates another nipple that I have no clue to where it goes. Hopefully when you hear back from the "Super Carb" guy...he will be able to provide a very good vacuum diagram....maybe.
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  23. #23

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    A few more pics. Red marks the nipple we've been discussing, blue is another unknown nipple. For the time being I ran the hose (red) into a "T" w/in the PCV hose to keep from having soot everywhere, plus it helps keep that noise to a minimal.
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  24. #24



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    The port does not go to manifold vacuum. It runs into a port in the manifold where the air valve draws it's air from, by passing the carb to lean out the engine. You have a bad air jet valve. It was confirmed by the guys at carbco. He is going to try to get us an exploded view of the carb. He said the diagrams we have are the same ones they have. I'm now at 100% on the jet valve problem. You can confirm with the vacuum gage. If you put it on the port it will whip back and forth.
    Time to pull the cover and get rid of the jet valves.
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  25. #25

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    I pulled the valve cover this evening, & right away noticed cylinder #2 jet valve was stuck. When I took it out, the tip end was missing, leaving it open. I welded the open end shut and reinstalled. I also removed the jet valve adjusters from the rocker arms, so now the jet valves will remain closed at all times. I think I’ll order the “JVE” kit and replace the jet valves.

    That did solve my problem….no more blow-back from that port. I’ll have to test drive it tomorrow.

    So are you saying that “No” vacuum hose connects to this port?

    Thanks for all the help/info.
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