1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Factory Carb Ajustments (Continued Issues...)

Discussion in 'Daihatsu Hi jet' started by Steve S83, Nov 26, 2021.

  1. Steve S83

    Steve S83 Member

    I've had to take a break from the Hijet for a while, building a house took priority but I'm back at and looking for some expert knowledge.

    Backstory, snapped timing belt. Had head re-built and I reinstalled it as well as the stuff you would expect when diving that far in. Truck sat for probably a year between timing belt and new head install. Fired up well, idled great. As soon as took it for the test drive, shifting from 1st to 2nd it bogged down and fell on it's face. This continued and discovered it was over fueling. Plugs were soaked, I could have run my chainsaw on what came out of the crankcase. Like an idiot, I started messing with the adjustment screws figuring that may be it and did not improve the situation. I've got 0 carb experience so I read what I could but shouldn't have been the one adjusting anything. Not wanting to spend the $ on a new carb, I took the old one out, cleaned everything up, filled it with some Seafoam for a couple soaks, made sure the accelerator pump was working etc... I was hoping it was just a stuck needle or float or something.

    Re-installed today and as before, will start fine and idle with some manual choke (choke is broken of course) and can keep it idling with the occasion pull on the linkage. I have my timing at about 10 BTDC in that 900-1000 RPM range.

    My question/need is does anyone have experience tuning adjusting/setting up the factory carbs? There is tons of information on the forum about what to replace them with etc. but I'm curious if there is someone with knowledge on where to start with setup on what I have. I'm sure me messing with the various adjustment screws didn't help so now I don't know if cleaning solved my problem or not. I can't seem to get it to idle without it over revving anytime I breath on the throttle. It rev's higher that you'd expect for just barely touching it then it stays at high RPM and doesn't drop right back to idle like you'd expect.

    Thank you very much!
  2. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    Please put the information on your rig in your signature line, of your profile. It makes it lots easier to give you help.

    First thing to check is what the fuel pressure at the carb is. As the trucks age, the charcoal canister on the vents for the carb and the fuel tank clogs up, and the tank can’t vent. It builds pressure as the fuel sloshes around, and since the fuel pump regulates fuel pressure with a blow off valve on the return one to the tank, any pressure in the tank get added to the 2-lbs relief pressure, and it gets higher than the needle valve which controls the flow into the float bowl can stop, and floods the truck.
  3. Steve S83

    Steve S83 Member


    Thank you, I will get my rig information in. I thought I had done that previously for the same reason. To check should I just hook up a pressure gauge on the fuel line coming into the carb and then route it from the gauge into the carb? I assume I need to have it running to show over pressurization if it's going to happen. Based on your message, I'm looking for about 2lbs to be normal and beyond that is over? Your message actually makes a lot of sense because when I first put the carb back on yesterday, I could rev the engine with the throttle linkage and it would immediately drop when I let go. After it ran for 15-20 minutes and warmed up, it would over rev.

    If I do find I have too much pressure building in the fuel line, how to resolve it? I believe I see one charcoal canister on the frame driver side below the air intake. Just take them off and clean them? I snagged a new fuel filter as well as it's just time, is the tank canister in the back by the tank or on in line somewhere? Can they just be cleaned out or do they need to be replaced?

    Thank you again very much!
  4. t_g_farrell

    t_g_farrell Member

    I had this issue on my Every van and just bypassed the charcoal canister for now by attaching the vent line to the vacuum for the canister together. Worked like a charm. I know its not the same type of vehicle but they are all very similar in a lot of respects.
  5. Steve S83

    Steve S83 Member

    Jigs was correct, well I had another issue but defiantly think the canister was clogged. Pulled the gas cap and the issue eased. I say eased because my timing/carb adjustment was all over the place because I was chasing that as the issue not knowing about the over pressurization. Additionally, I've never owned or worked on a carbureted vehicle with vacuum advance. I'm in my 30's so it's been TBI or EFI for everything I've owned. Also, I'm no mechanic. I can usually figure it out but I would never consider myself a true gear head like some of the folks on here. Just don't have the knowledge or experience. Bottom line, I didn't remove the vacuum advance hoses when I was setting up the timing. I never had enough timing in the thing combined with the fuel issue just caused all kinds of problems. Did some additional reading here on the forum and read the correct way to time it and that plus the gas cap, first drive in almost 3 years!! Super stoked. Everything is working great. Now just need to find a thread on pulling the heater fan so I can clean the mouse hotel out of it!
  6. t_g_farrell

    t_g_farrell Member

    Good to hear. Yeah a lot of us grew up with carbs so they are second nature to diagnose and adjust. Its very analog compared to EFI for sure.
  7. Steve S83

    Steve S83 Member

    My issue was that I assumed I had the timing side correct. Then I kept adjusting the high idle screw too far down to maintain idle. Then when I gave it gas, the butterfly in the carb wouldn't close back all the way because the idle screw was holding it open. That combined with the pressurized tank was causing me fits. I did the head almost two years ago and it's been sitting because I was building a house. Picked it back up last week and so happy to have it running. Since the previous post I took it for a good shakedown and everything is working except the heater fan as I noted earlier. Happy there wasn't any mouse damage to wiring or hoses. Thanks again for the help.
  8. Steve S83

    Steve S83 Member

    Calling out to anyone who can help a complete newbie to carbs dial mine in. She runs and drives finally after 2 years. Head and valve train is all new. Water oil and accessory drives are new. I thought it was a junked up carb until my father in law dropped some knowledge that you have to pull the vacuum advance off when setting initial timing. I thought the overfilling was due to the carb and the clogged charcoal canisters may have contributed but it was my inexperience with carb/distributors. Bottom line, she is running and driving.

    Now I need to dial in the carb and am lost. My understanding based on the forum is that the screw on the very top of the carb directly above the throttle blade is the fine adjustment screw for fuel/air. The two screws in the front of the carb are to set the idle speed when warm. One for warm idle, the smaller one for warm idle when under load from alternator, AC etc. I don’t know id this is correct but again, best info I could find on the forum. Choke is busted so that’s manual so no cold idle adjustment. I have the larger of the two warm idle screws backed out as far as I can without the engine dying. This puts my idle somewhere around 7-800 RPM (tach is in the mail). However the idle jumps around up and down sometimes due to electric fan, sometimes for no reason. It’s running relatively smooth but still has a shake or shimmy now again while idling. And advice on where to go next would be greatly appreciated. Thank you!
  9. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    Warm idle is about 900 to 925-rpm. It won’t smooth out, down around 700 to 750-rpm.
    t_g_farrell likes this.

Share This Page