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Thread: 86 Ram 50 2.0l Carb adjust for smog....Help?

  1. #1

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    86 Ram 50 2.0l Carb adjust for smog....Help?

    Hello all, here is my first thread.

    I just bought 86 Ram 50 2.0l with Auto Trans. The truck needed alternator and carrier bearing on driveshaft-done. Then oil pressure sensor for light-done. New NGK platinum plugs. Now moving on to getting ready for smog.

    So I opened the air cleaner to find the barrel of the Carb with a 12 gauge solid core wire twisted to the bore, preventing the water choke from closing all the way. I took the wire out to see what happens. Choke butterfly closes all the way when cold. Truck starts and dies immediately. If I hold the Accel. pedal down it starts but smokes like crazy. Way too rich. I put the wire back. It starts fine and idles up to operating temp. Progressively, as temp increase choke flap open more and more until wide open. I think it is working fine in respects to opening, just too far closed at cold start.

    Once warm the truck seemed to idle too high. I connected a DVOM with RPM function to coil negative and battery. The meter reads 1090 rpm. Spec is 750 +/- 100.

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    In this picture it displays the MAS (mixture adjust screw). The plug is already removed. I tried adjusting 1/8th turn by turn until I got the highest rpm. I don't know if this is right but I basically just tried to tweak it until rpm peaked.

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    Now my idle was at 1100. But all the while it was smooth as can be, not missing a beat.

    According to a couple other write-ups and alldata the SAS-1 from diagram is the one I turn to adjust idle rpm. Well I tried turning 360 degrees both in and out- nothing.
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    So I tried to put it back where it was. Next I moved on to SAS-2 and SAS-3 from diagram. I turned both in and then out 360 degrees (seperately) made no difference.
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    I thought maybe the throttle cable was too tight or the kickdown rod for trans. I checked, they are not the ones holding IDLE high.

    Last after looking for awhile I found this screw
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    It doesn't seem to be located on the diagram, or maybe I don't interpret it right. The screw is located below the choke linkage and behind the choke tamper cover. But sure enough it lowered the idle to 850rpm is where I left it.

    The truck is still idling smooth but I am not sure if what I did is correct as far as the other screws or proper adjustment. If any one can offer some suggestions. I believe the truck was originally running too lean, previous plugs were white. I am pretty savvy with cars but carb is just before my time. I am trying to learn though.

    Another Question, how does the Oxygen sensor come into play? Alldata said once warm, test voltage output with DMM- should be higher than .8??? mine is .02? Broke or super lean?

    Thanks. Sorry if my pics aren't visible, my first detailed attempted write up.

  2. #2



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    You need to lean drop the carb. Engine warm.
    Just turn out the idle speed screw tell it comes off the seat. then turn it back where it just touches. Then turn 1/4 more turn. Then back out the mix screw so it runs. Now turn it in untell it dies. Then back out 1/4 to 1/2 turn. Next use the idle speed screw to set the idle rpm. should only need to move about 1 turn.Your done. rev tuen it a couple ot times and then shut it off. Engine run on should be gone. Good luck
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  3. #3

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    Setting the speed adjust screw (throttle stop) requires that you can see when the screw is wound out to the point where it is no longer supporting the primary throttle linkage, then wind it in until you can physically see that it is touching the linkage again. Now adjust the the screw marked SAS-3 (fast idle adjust screw) until you get your idle speed set. The throttle stop and fast idle adjust are 2 screws that need to be set after a carby rebuild before it is installed. The primary throttle butterfly should be cracked open just enough for light to pass through it so the butterfly isn't jammed up against the throat wall.

  4. #4

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    Thanks to all.

    Camoit, thanks for the guide on getting started. Big help! I think maybe the chokebreaker rod or spring is MIA.

    Geezer101, thanks for the info. So the fast Idle is the SAS3??? It seems that I got it pretty close to adjustment right now after some help with Camoit. I just have no cold start fast idle. It idles way to low and wants to shake and die. If I use foot pedal to warm up, then its good. I dont mind too much but the misses hates it when she drives.


    Looking at the above diagram compared to the real pics I took, would the SAS3 fast idle be the third (3) pic I took or the fourth (4)? It just gets confusing, there are three (3) SAS screws in diagram but four (4) screws in real life????

  5. #5

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    The fast idle adjust screw is the one hiding behind the throttle linkage where the accelerator cable hooks up (a screw with a captive spring sandwiched in it) The Mikuni carby is a tricky thing to set up, and it will make you want to claw out your eyeballs in frustration if you get an engine with one fitted to it and it has been messed with randomly.

  6. #6

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    ok I am going to go try right now! The eye balls scratch out has happen a long time ago!!! Its almost time to smash with a hammer.

    Now when this thing starts on cold morning, it should have a fast idle of about 1800-2200 rpm right? And then drop down once warm...at least that is what I would guess. Mine tries to idle at what ever the idle was set at when warm. then it idles like sh*t.

    Do you know what could be missing from fast idle mechanism?

    Appreciate your help!!!

  7. #7

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    Geezer101,

    I went out and started it from cold start, once warm I got the thing dialed in good and smooth following what you said. However, the last thing I trying to figure out is how to get the cold start up better. Pretty much if I leave it adjust the way it runs good warm then it wont cold start for sh*t. There seems to be no fast idle when cold.

    I found one more screw on the throttle linkage side, from where you described the sas-3 is (below the choke plate, by throttle linkage) within that screw, about .5 inch below and angled down. It has the spring on it aswell. It was backed all the way down. Do you think this can effect the cold fast idle?

    Correct me if I am wrong, you should jump it hit the gas to floor to set fast idle, crank it, it starts at higher rpm until warm, then lowers idle. That sound like normal process? this doesn't idle high. It starts, idles at 700 like shaky hell, then once warm perfect and at 750 rpm.

    when I romp on it bluish-gray smoke from tailpipe.

    Today it passed smog, only cuz I cheated. Brand new cat. Its pre-cat levels were 350 Hydrocarbons, .4% CO. After Cat 28 HC-0.0 CO.

    I just want to get it to start nice so wife can drive when needed. Now I need to baby it.

    Thanks again.

  8. #8

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    To me it sounds like the fast idle screw is adjusted all the way in - this what you got? This screw should have a fair bit of adjustment left on it under normal circumstances. The spring should not be compressed more than 5/16" or 7mm (what it looks like to me anyway...) I would (this is gonna annoy you ) wind out the fast idle adjust screw, reset your throttle stop screw and then try dialing the fast idle screw back up until you get into the ball park. You'll get there, only a matter of time and a bit of patience.

  9. #9

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    YEP! That little hidden screw that is way down there, bottom of "bell crank" I believe is the name is the fast idle choke adjust. You have to rotate the throttle linkage for the screw to come into view. I adjusted it last night. It was completely backed out. I turned it in 10 turns.

    This morning I went out and started truck. I still have to prop open choke plate 1/16 inch with wire down air horn, but not too concerned with this. Then I started it----wait for it-----purrs like kitten at 975 rpm. As it warmed up dropped progressively to 750 rpm, which is what i set it at yesterday.

    I will try one more test time to call it as good, not fluke accident. If it correct and I am not talking out of my *ss then I will post pictures of the screw that I am referring to.

  10. #10

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    YEEEAAAAH BABY! You will become a Mikuni carby master in no time. Hope it wasn't a fluke, but it shouldn't be. Now you can get down to enjoying your truck without your wife doing this at both you and your truck. With some fine tuning it will be running like a new watch.

  11. #11

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    does it blow black smoke til warmed?....could be choke needs to be adjusted to open sooner by 1 tooth (screws face towards the firewall, use stubby phillips to access bracket, careful not to lose spring)...this fixed my rough idle/smoking issue...chokes are overrated.

  12. #12

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    Just tried for a second time-Perfect idle upon starting.

    Finally I can go to sleep! Up for days on this thing-obsessed.

    It only blows smoke if I romp on it when its cold, at idle its good. The choke is still a little funny, it stays all the way closed at cold start up which is too much. So there is a piece of 12 gauge wire wrapped around the center air cleaner bolt then one leg of the wire going into air horn to prevent the choke from closing all the way when its cold. Its the perfect amount. I was thinking of trying to adjust it but I would have to grind off the choke cover plate to gain access and that seems like a headache.

    ragragtimtime: I thought I read somewhere that the choke unloader is supposed to pop the choke plate open just a crack upon cold start to prevent overenrichment. I don't believe this is working. When I try to peak around the cover it looks as if all of the parts to the unloader are there, just for some reason on cold start choke plate wants to slam all way closed. Do you think if I take it apart and adjust it one tooth like you said it would cause the choke to not close all the way? If it might work, then I'm all over it. I am happy with it but I have been told i have OCD.

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    Doesn't that truck have one of them egr sub valves on the drivers side of the carb? Darn things get all carboned up and clogged. Use to pissed me off when the gas peddle would actually get stuck temporarily from that thing getting stuck in the carb from muck on it. Weber fixed it all!

  14. #14



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    how are you starting the truck - you should push the pedal to the floor once to close the choke, then when it starts, hit the pedal again to drop down 1 notch on the cam. If it doesn't work that way, your linkage is hanging up for the choke. The choke adjustment ragrag timetime mentioned is important also, as the choke is a spring that unwinds when it heats up to open the choke, if it is wound too tight it will open slowly, if at all; too loose and it won't set
    Pennyman1
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  15. #15

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    Bradmph- yes it does have the subegr. Thanks to Camoit, he schooled me on the components and their location. We tested the subegr for operation it works. Also the presmog inspection showed that the Nox was under control so its doing its job. I have been thinking of going Weber in between smog checks but I am on the fence.

    Its funny I bought the truck for a beater that i was going to use to move only, now I am liking more and more as days go on.

  16. #16

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    Quote Originally Posted by pennyman1 View Post
    how are you starting the truck - you should push the pedal to the floor once to close the choke, then when it starts, hit the pedal again to drop down 1 notch on the cam. If it doesn't work that way, your linkage is hanging up for the choke. The choke adjustment ragrag timetime mentioned is important also, as the choke is a spring that unwinds when it heats up to open the choke, if it is wound too tight it will open slowly, if at all; too loose and it won't set

    So for these last 2 tests I start it as follows- I push pedal to floor quick and fast 1 time, then start truck. Watch it idle at 900-950, over about 10-15 mins the choke plate opens slowly and in conjuction with the temp rise. until it is wide open and truck is now at 750 rpm (spec). I haven't tried to hit the gas down to knock it down. I will try in morning along with try to get some detailed pics of it. as far as I can tell the choke works normal just he plate at cold is 100% closed. It wont start right there, but with the width of 12 guage wire in between the airhorn tube and the choke plate (butterfly) it starts up and purrs.

    You think I should try to adjust the choke gear? grind off the plate screws and move the gear one tooth.

    **sorry if my terminology about Carb is off. I am pretty good with cars, but never really messed with carburetors. When I got into the field they were on the way out so to speak. I am more of a OBD2 and Modis kinda guy.

  17. #17

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    I would say at this point you are ready to go to phase 2 - choke butterfly adjustment. The choke butterfly should only barely be loaded up when cold - a light tap with a finger and it should flap open and closed (in fact engine vacuum when cold should be enough to pull the choke butterfly open slightly, that is how much pre-tension should be on it) So,here's how to adjust it. I'll do my best to not make this sound too complicated.

    On the auto choke assembly there's a mounting bracket with geared teeth cut into it (it is held in place by 2 small phillips head screws). Undo both of those screws but not to the point where you remove them - enough to free the bracket will suffice. Now, if you grab the upper end of that bracket you can raise and lower it, this in turns adjusts the pre-load on the choke butterfly spring (the top mounting hole is an adjusting slot). Raising it should reduce the tension on the geared sprocket. Once you have it set at a point where the choke 'soft closes' tighten up the mounting screws and you should be ready to go. Hopefully this will cure your choke issue.

  18. #18

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    please take pics! I don't recall "grind off the plate screws" issue. just a simple bracket with phillips head screws facing firewall (need stubby handle..not alot of room). also "over about 10-15 mins the choke plate opens slowly and in conjuction with the temp rise" time is way too long! where is the temp guage when fully warmed? should initially go up slightly above half then stay slightly below half (may have worn/wrong thermostat..."the" mitsubishi manual says should be 88c/190f or more...must have a "jiggle valve" on thermostat to allow antifreeze to pass & get to wax element in carb so choke will open). you mentioned new plugs...check the condition now & after making adjustments/changes. nothing wrong with OCD if it gets you better fuel economy & performance

  19. #19

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    I dun goofed with my adjustment advice - lower the arm to back the tension off. You would've figured it out anyway. And the auto choke should open within a few minutes of running under normal conditions. The temp gauge needle should reach the centre marker and hover around there as ragtime has indicated too. If it doesn't then it would be advisable to check out the condition of your thermostat. Pumping the accelerator pedal while warming up will disengage the auto choke approx 50%, but will still need to reach running temp to open which should only take a few minutes under normal driving. The wax pellet in the auto choke doesn't operate at the same temp as the thermostat.

  20. #20

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    I think I may have over estimated the elapsed time of warm up. However, I do believe the tstat sucks. The gauge never gets about 1/3 way. Going to get new thermostat , take pics and time it today. I have to do a few things first but will try to have up this afternoon.

    Thanks for the advice and comments. I really appreciate everyone on this site! It seems to be a good community.

  21. #21

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    Thermostat was stuck open- slowing warm up time- replaced with new - and same time new wires and air filter because I found brand new ones on a donor vehicle while at junk yard.

    When I was at junk yard I pulled a carb off the recently junked ram 50. I inspected the linkage, choke mechanism and which adjust screws do what. Once it was off I could tell easily what was what. I took some pictures so we have it on record.
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ID:	10923This one is for choke High idle adjust. You can see its on the bottom of the linkage. When its on the truck its almost not visible. If you have someone sit inside and push gas pedal to floor it comes into view.
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ID:	10924This one is the SAS1 idle rpm adjust, use this once it is all the way warm.
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ID:	10925I thought this was originally for idle adjust rpm, but when its off you can see its very far away form anything. If you take it all the way down it will stop the throttle from coming down closed but I am pretty sure thats not its intended purpose.
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ID:	10927two more pictures of warm idle rpm adjust screw and choke high(fast) idle screw from a distance to get perspective of location (pics in order described)

  22. #22

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    Ok here is the breakdown of Choke issue I was having and the solution:

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ID:	10928So everything was working, except the choke closing too much at first start up flooding it. So this piece of wire was used to shim out plate. It would run perfect with this plate, but is "shade tree". Taking it on advice from some wise members I decided to remove choke access plate and adjust the gear for the choke a few teeth.
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ID:	10931to get this plate off you have to grind off rivets and then unscrew 3 screws but the heads have been ground off for security.

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ID:	10932I taped up the carb to prevent things from flying in there while I was using the dremel to cut off the plate. I did this entire thing on the vehicle.
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ID:	10933After grinding the 2 rivets I used a cut wheel to put a notch back in the 3 screws and then used a screwdriver to remove cover.
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ID:	10936This is the choke mechanism before I tried to adjust.
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ID:	10938In this picture you can see 2 brass screws that hold the choke adjusting gear and plate to the carb. They are 8mm is size. If you loosen these you can pull the plastic gear out and spin it to tighten or loosen the force of the choke plate against air horn. In my case I needed to loosen 2 teeth. The top screw has a slot so once in place you can fine tune adjust the choke plate. *****The bottom screw hole of the plate sits on a extruding stud, to prevent sliding. I snapped the head off my screw like a dumbas*!!!!!!!!!!!!!!
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ID:	10939Reassembled and the perfect choke clearance was there. Started truck, ran perfect, came to operating temp, High idle is good and drops to 750rpm. Everything is great! just that broken screw. I dont think that plate is coming off but the only way to get a screw extractor in there is to pull the carb!!!!! I dont want to but lets see how it goes. sometimes I get a wild hair..

    Thanks for everyone's help!!!! Do you think the other screw Is enough to hold the choke adjuster plate on or should I try to get the broke piece out?????

  23. #23

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    O.k. now I get that 'grind off the plate screws' thing. That is a b*stard act to tamper proof a carby, I have never seen a Mikuni with a guard mounted to it like that... It was really out of adjustment if you needed to bump the choke butterfly gear 2 teeth to get it back into working condition! And it is a rare occasion where you can pull any screw off a Mikuni without chewing the head out of it - they are locked in pretty tight. But it looks like you have defeated the beast - good work

  24. #24

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    thank you! Oh I just went out with screw extractor and mounted in right angle drill attachment for dremel and fished out the broke screw I busted. Relieved!

  25. #25

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    to ease your mind (til you get a "wild hair")....how about a few drops of thread sealant (ie-loctite or permatex) on the non broken screw & how do the plugs look now

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