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throttle pull down - rpm drops too slow

Discussion in 'Daihatsu Hi jet' started by wheelio, May 22, 2020.

  1. wheelio

    wheelio New Member

    First I want to thank all posters on this site for sharing their questions and answers that help so many.

    I have a 1994 Hi Jet S110P EF-NS and i am having trouble with the rpm's not coming down fast enough after the clutch is depressed while shifting. I think it may have something to do with the "fast idle pull off" but i cant find more info. I have checked for vacuum leaks near the carburetor with brake cleaner and propane and found none. I considered replacing all the vac lines but they are still flexible and Seriously numbered.

    I keep looking and will update my post if i find what vac line pulls the throttle down.
  2. ttc

    ttc Active Member

    Have you inspected all the vacuum lines? The ones that where cracked on my truck looked fine from outside. But on the. Cut end there was cracking from inside out and the cracks where with the length of the hose. If your rpm doesn't drop you may have a lean condition.
  3. wheelio

    wheelio New Member

    The vac lines checked out but the carb linkage was a little sticky so cleaned it all up. Not much better so i tried adjusting the carb. It is a bit better, idle drops faster, slightly less power. Still think i need a vacuum gauge, labled diagram or photo and adjustment procedure for my carb. Im having trouble uploading an image of carb but will try again later. Might reach out to Reese Allen i heard he might have the same model truck we have met before and i think lives nearby. getting closer
  4. wheelio

    wheelio New Member

  5. wheelio

    wheelio New Member

    Okay i got a vac guage and an inductive pickup for my meter so i can see the rpm's (tach couldn't sense the coil - terminal).
    I zeroed out all the screws and I popped off the plastic cap on the air mix, turned it until it seated, then backed it out 3-1/2 turns.
    I think I set the throttle plate screw to when it just stated to move.
    I started the warm truck and opened the air mix screw to get it to idle better at around 5-600 rpm.
    I adjusted the lo idle screw till it raised the rpm to 900.
    I opened the air mix screw until it was about 90 degrees CCW from starting to get lean (run rough) and put the plastic cap back on centerd. Turn it right- rough, turn it left- nothing.
    The vac gauge just showed in top of the green zone (20) at idle, disappears (0) when throttle revved, goes up just a little beyond zero when you let it off before dropping back again and it bounces if air mix is turned to lean (CW).
    The throttle response is much nicer and it has much better low end torque, even when driving cold.
    I went to set the cold high idle in the morning, 1200 no problem but then it started revving higher as it warmed so i ended up backing it way off.
    I need to re-verify what all the adjusting screws are for and review how to set the choke and understand it works a little more too. The little white plasic cam and spring (on the choke i think) hardly moved at first but after a bit of cleaning I got it to move but it still feels pretty tight compared to a youtube video Ive seen. I would like to figure out how to adjust the spring pressure and why.
    I found someone in town that works on these trucks for a living but it was difficult to communicate due to language. He kept pointing and focusing on the lo idle and air mix. My understanding he was saying only adjust those two. I felt he may have agreed with me on the labels in my picture but not sure. Right now it runs much better but takes a while to warm up on the low idle. I'm missing something and when i figure out what every adjustment does I can finish this all up.

    I'm still getting closer.

    to upload an image I have a Mac and I just had to save the image as a (.jpg) instead of the default (.JPG) before uploading.
  6. Limestone

    Limestone Active Member

    Did you review the Carb. maintenance tips on G$R Imports? I think the info and diagrams might help a little!
  7. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    Your labeling of the screws is off. The one you have labeled as high idle, is the high idle for when accessories, such as the A/C or PTO are engaged.

    The choke high idle is the one to the bottom left, marked “Plate Adjust?”

    Your beginning was correct, but I’m not sure you gat the best lean idle part right: Set the idle as low as the vehicle will run smoothly. This should be at least a hundred rpm or more below the Normal idle speed. I got my Hijet down to 650-rpm, 300-rpm below the stock idle. You’re assuring that the idle circuit is the only one delivering fuel to the engine.
    Then turn the idle mixture screw in a quarter turn. If the engine speed increases, reset the idle speed back down. If it goes down turn the mixture screw back out a half turn and see if it goes up. You’re trying to find the sweet spot where the engine is running as lean as possible. Keep adjusting the idle mixture, and rpm, until the engine is running as lean as it can and still run well.

    Then reset the idle to what ever yours is supposed to be at, my S110P, is 950-rpm. There isn’t a cold idle speed listed, but typically engines are set to about 300-rpm above the hot idle, so I set mine at 1250. It wasn’t quite right when the temp got down to -20F, so it is now at around 1500, when the temp is around 40F. I noticed that there has been some wear in the cold idle cam, and there is a flat spot where the stock index mark is on my carb, and that might be why it is a little higher than I would like on chilly, but not cold mornings.

    Hopefully, I’m headed to the shop later today, to work on wiring a trailer light plug. If I make it I’ll take a few pictures of the spare carb, and annotate it to clarify what screws do what.
    Limestone likes this.
  8. wheelio

    wheelio New Member

    Not getting closer,

    Okay If i turn all off and only raise the Lo idle and air mix to get a good idle it runs great. for cold high idle, opening any screws on the side just raise the idle more or cause a power loss in the middle of the acceleration curve. the only jdm vehicle mechanic doesn't speak English but i might try taking a translator. I need to understand exactly how the choke functions better. Thanks again for all the help and suggestions.

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