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Thread: High idle issue

  1. #1

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    High idle issue

    So i rebuilt the mikuni carb on my 85 power ram 50. 2.6l engine idle high before i rebuilt it. I suspected a rich condition or screw issue, so i fiddled with th screws. Obviously nothing happened so i found myself here where i learned i shouldnt have done that. So yeah i rebuilt the carb, put her on, and she still idles high. Before i put her on i adjusted the throttle plate stop till it touch, then a 1/2 turn more to start with. I have adjusted the other idle screws while running but this time i counted my turns, but the idle never changed. I am going to try turning the high idle screw with the captured spring in and see if anything changes. I am also going to try turning the fuel screw in till it wants to die and then back it out 3/4 to 1 turn out. This is all i know to do. I do not think there is a vacuum leak since the mounting gasket is new. Any advice would be very much appreciated.

  2. #2

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    I turned the fuel mixture screw in till it bottomed and she still ran. Idled a bit high still, i believe. My next question is if any of the 3 little electric solenoid things controls fuel. I removed and replaced every oring and cleaned every jet i found

  3. #3

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    The air fuel screw will almost kill the engine but it needs to be out 1 1/2 - 1 3/4 turns. The solenoids are internal air circuit controllers that regulate fuel supply between the idle, primary and secondary fuel. Does the idle stay high regardless of engine temp? And does the choke butterfly open at all/is locked tight at cold start? The choke might be the problem but it's a process of elimination.
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  4. #4



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    I just have a simple question, How come you didn't purchase a Weber carb and simplify all your problems that the Mikuni carb can create, to almost none? You would of also gained some performance on our older trucks. It is a very beneficial update for the truck.

  5. #5

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    The reason i did not go to a weber is because the farmer i work for didnt want to put out the 250 for the kit. The truck is used to haul the welding equipment so he couldnt justify the money.

  6. #6

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    Im about 90 percent sure tbe coolant choke actuator is stuck fully extended. I locked the choke gear open at all times. I would like the choke to work but i do not know where to find a new coolant choke to buy. Im going to try and pull the fuel mixture seat to see if its bad. It didnt die when i bottomed the needle but it didnt stumble either. This is only my second carb rebuild ever so im trying to learn. How can i add pictures here?

  7. #7

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    It was cool this morning so when I got to the truck I turned the throttle stop and the 2 idle screws out 3 turns each but left the captive spring screw alone, I have already turned that one out a ways. Started it with ether since the choke is open and she idled fairly well, don't know what RPM since I don't have a way to tell. Once she warmed up though I heard it kick up a bit. Know that the arm going to the throttle stop adjusts fuel when choke is on, am I right on that? Another thing to note is a few years ago I believe it was idling high and I did tweak the distributor timing without a light. I was fresh out of my mechanic classes and I heard the idle kick down with the distributor so I was happy. I have a timing light now but with the idle high I don't see the timing mark so I spect its because of the high idle, I could be wrong. This truck is a mess and I am trying to fix her up.

  8. #8

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    Normally the wax pellet choke bleeds out and the rod collapses into the housing. If it is protruding a bit it should mean it's serviceable. DO NOT USE THE DISTRIBUTOR TO ADJUST RPM/IDLE. This will set up a death spiral of fault diagnosis and to the uninitiated, this means adjusting a bunch of screws to get it to 'sort of run' but have engine misses, lost power, detonation, and generally poor running. This then leads to the 'these engines are junk' mantra. Check timing marks and distributor installation first, set idle rpm off the carb, then proceed with ignition tuning. Once you know the base timing and idle is good, start retuning the ignition to extract better performance.
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  9. #9

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    I know adjusting with the distributor was wrong, i just didnt know any better at that time. Could i adjust the distibutor till it gets in the ballpark then adjust the carb right and then fine tune the distributor timing? Also, i have the throttle plate screw backed off and the 2 others backed off a few turns but she still idles high. I sprayed starting fluid round every vacuum port i could find and it didnt make the engine change.

  10. #10

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    Try backing off the advance on the distributor until it conks out or idles really low, then wind in the throttle stop screw until the idle picks up. Give the throttle a few turns and watch how it responds. If it's hesitant, give the distributor a little advance and try again. This is not going to be easy without a timing light but the timing light really is nothing more than a diagnostic tool (so many variables with trying to set an engine to factory specs and actually get it right). You can get an engine to perform a lot better by 'tuning by feel' but only after you've got the basics right.
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  11. #11

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    I do have a timing light so i will give that a try when i can. Thanks

  12. #12

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    Im looking into it again now. Adjusted the distributor to see if it changed and it did nothing. I figured as much. The idle is too high that it must be advancing a bit. I decided to put a rag in the carb to choke out air and begin looking for a vacuum leak. It dies out so im happier. If i stuff the rag in the secondary throttle hole it dies. If i stuff a rag in the primary hole and leave the second open it just goes real low and almost dies but still runs. So i spect ive got a air leak on the secondary throttle plate. When i shine a light down the hole i can see the plate is open a bit so im trying to find the screw to turn out and shut the plate. I did notice something odd though. On the plate there is a tiny piece of metal, like a little strip, that i think might be holding it open, ideas?

  13. #13

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    Ok finally the engine is changing. Took the carb back off and sure enough there was a small metal shaving keeping the secondary throttle plate open. Put the carb back on and adjusted the throttle stop screw in till it touched and a half turn more. I turned the fast idle screw, which is the screw with the the captive spring as i understand, out till i knew it wouldnt lose the spring so that i could adjust it in. Tried starting but didnt want to stay running so i have turned in the throttle stop screw a few turns to keep her running atleast. There are 2 screws near the throttle stop screw, one is connected to the little dashpot, that i turned in but no change occured so i turned them back out. I have turned the fast idle screw in a couple turns but i didnt hear no change, but i left it turned in for now. When i can get a skinny screwdriver i will try and lean drop it with the fuel screw, would this be ok? Sidenote, i turned the distributor a little to see if it made a difference and it did. I am not tuning by the distributor i just wanted to see if i was low enough in the rpms to take off the advance.

  14. #14

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    You were lucky the chunk of debris you found didn't make it into the engine. I think you're on the home stretch to getting it running right.
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  15. #15

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    I think i am too. It was finally idling lower. It was idling rough so i opened the throttle plate enough to keep it running and turned out the fuel screw till she smoothed out, im out 3 full turns now. Idk if it is right but for the sake of needing the truck i am going to leave it. It drove and didnt pop or backfire so im good for now. It does have a stumble off idle when you lush the throttle so should i add more fuel or less? Also, the fast idle screw with the spring, does only affect ths idle when the choke is on? I appreciate all the advice yall have given me.

    Caleb

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