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Thread: Need help with mixture settings on my 660cc

  1. #1
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    Default Need help with mixture settings on my 660cc

    When I bought my 1992 Daihatsu in November I drove home (Victoria BC to Quesnel BC) with my 200kg BMW F650GS motorcycle in the back and could get the truck up to an indicated 105km/h on the flats with ease. At idle I could smell fuel in the exhaust and it had trouble starting when warm on occasion. After soaking the carb with WD40 and making sure the linkages were all free to move the truck ran and started great in all conditions - I can even start it at -32C without plugging it in - can't complain at all with the exception of my top speed. My max speed empty is 95km/h and it takes some time to get there - 85 is never a problem but after that it creeps up to about 95 and that's it. I can never smell fuel in the exhaust at all since the freeing up of the carb. I would like to be able to crack 100km/h again - part of the reason for getting the Daihatsu in the first place - my guess is that now that the carb can move freely, the mixture is a little lean. I know nothing of carbs - computer control VW TDI engines are no problem for me but carbs... ack! I don't want to mess up anything so I need advice.

    What are the three screws shown in this picture? What one do I have to turn to richen up the mixture a bit?


  2. #2
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    I am guessing "A" looks like mix screw. As many dealers up there in CA should be able to find someone that knows. If not try Daihatsu America Tech. Assistance 800-777-7070, or better yet "Daihatsu Help"
    (Leon)626-333-7897 Tech. Assistance. Leon has some pretty laid back hrs. but he knows these little trucks. You can get a service book from Lulu Publication.

  3. #3
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    There is already info here from another that has pictures. He put the whole book on for us to use on the site.

  4. #4
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    Go back to hi jet and click on the red writing and look for mgeorge.

  5. #5
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    The page ray is refering to is here

    Just remember there is a few things that don't apply to your truck like the "25 mph" cutout circuit.

    The basics should be the same though and get you back on track
    '91 Subaru Sambar SC KS4 c/w Diff Lock
    Dyno'd at 69 HP@ Rear Wheels 61.5 ft/lbs torque

  6. #6
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    I don't mean to come across as a dump ass here... but I have already looked at that manual.

    Page 11-24 show part #3 is the mixture screw, part #4 goes under it which is a spring... so looking at my photo this is either A or B as screw C has no spring under it. My problem is that the book's diagram doesn't really show, as least for me, WHERE it goes on the carb. I can't tell from the photo if it has a round or hex head on it. I don't see that 2nd screw in the diagram either so that's what makes me unsure. Exploded diagrams are one thing - photos are something else that I can understand better in some cases like this. I don't want to screw things up (no pun intended) as this is what my wife drives on her job every day... pissed off wife equals...

    Which way do I turn for a richer mixture?

    Thanks again.

  7. #7
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    the mixture screw is really only for when it's idling. anything more than that it is drawing from the idle jet up to about 2500 +/- and then it goes to the main jet. by adjusting those screws you will see no gain or loss other than when the truck is running at an idle. i would look into the ignition system. if you have a distributor i would check your points, condesor, cap & rotor. also make sure to check that the timing hasn't moved. depending on the mileage of the truck i would also consider the timing belt. if the timing belt is aging it will stretch and the valve timing will not be in sync with the crank. with all that said... how many miles have you got on the truck? i believe the timing belt is recommended to be replaced every 60,000 miles or 100,000 kilometers.
    Stone Soup Metal Works - Personalized Welding & Fabrication Services
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  8. #8
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    I think "C" is the idle mixture.
    I think "B" is idle speed screw
    I think "A" is high speed or main jet

    As for idle mixture I would think that because it is a air bleed and not fuel that the screw adjusts then turning it in will
    give more fuel [richer] and backing it out will make it leaner.

    The main or high speed should be the opposite as it should control the fuel passage so you would back it
    out to richen it up.

    As Milt said in his post there might be more to look at than just the carb

    On my Sambar the timing belt interval period is 60k kms not miles.
    '91 Subaru Sambar SC KS4 c/w Diff Lock
    Dyno'd at 69 HP@ Rear Wheels 61.5 ft/lbs torque

  9. #9
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    one more thing to consider, as with the inginition parts, is that you have to consider the fact that unless your garage has gremlins in there, the lack of performance is probably due to degradation of something. i ran a speed shop for several years & guys would always come in and say "my carbs got out of sync". after looking everything over i would usually find that they were making adjustments that lead to the poor performance. if you have made no adjustments to the carb since it used to run 105KPH chances are the carb is still in good standing. before you start making adjustments make sure they are necessary! i can't stress that enough. if you start making adjustments when the carb is not the problem - it's only going to make it harder to tune the motor in later. find the real problem first. i know i've said this enough to sound like a broken record on here, but honestly i have seen so many people turn to the carburetor when it's an ignition problem. lack of performance is not always the carb!! you need three things for a motor to run - fuel, air & spark. the most comonly degraded are the air (air filter) and ignition (points, condensor, cap & rotor).
    Stone Soup Metal Works - Personalized Welding & Fabrication Services
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  10. #10
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    I have one and have rebuilt and adjusted the carb with good results,

    A Idle adjustment (warm..off choke)

    B Fast idle adjustment (idle speed choked)

    C Mixture adjustment

    Hope this helps

  11. #11
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    Quote Originally Posted by Mighty Milt View Post
    one more thing to consider, as with the inginition parts, is that you have to consider the fact that unless your garage has gremlins in there, the lack of performance is probably due to degradation of something. i ran a speed shop for several years & guys would always come in and say "my carbs got out of sync". after looking everything over i would usually find that they were making adjustments that lead to the poor performance. if you have made no adjustments to the carb since it used to run 105KPH chances are the carb is still in good standing. before you start making adjustments make sure they are necessary! i can't stress that enough. if you start making adjustments when the carb is not the problem - it's only going to make it harder to tune the motor in later. find the real problem first. i know i've said this enough to sound like a broken record on here, but honestly i have seen so many people turn to the carburetor when it's an ignition problem. lack of performance is not always the carb!! you need three things for a motor to run - fuel, air & spark. the most comonly degraded are the air (air filter) and ignition (points, condensor, cap & rotor).
    The power went down after right after I sprayed the heck out of it with WD-40 and worked on the loosening up all the linkage for the choke system so it would re-start.

    The timing is dead on spec - an advance does occur. Timing belt looks good. I have not changed the rotor, nor cap, nor plugs. But have changed air and fuel filters.

    The truck runs like a champ, just lacks top speed and the finger in the tail pipe comes out clean which to me means it is running lean.

    The only "issue" with the truck at this moment is a rotten muffler - the tail pipe fell appart and the rest of the system looks pretty rusty. I am considering a Supertrapp motorcycle muffler so I can play with back pressure. Maybe it is being more restrictive now than it should...

  12. #12
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    sorry to cut in here but dose any body know where i can get an exploded view of a 92 diahatsu carb,i would like to rebuild mine ,but would like to see what i am getting into .

  13. #13
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    OK... my truck ran great for about 500km and now it is dieing while driving. Turns over with plenty of speed just no vroom - no rich smelling from the exhaust and if I let it cool off it starts up with no problems. Towed it back home and now that it is cold fires up, let it warm up and then it starts again and again no problem. This is the wife's truck she uses on the job - now she pissed. Tinkering tonight I can add the following to my original posting:

    A - Mixture
    B - Warm idle speed
    C - have NO idea
    D - Not labelled in the photo, but it is the screw with some yellow paint on it in the photo attached to the throttle valve - this is the cold idle speed.

    Right now I have a good sounding idle at the cold setting which is slightly higher than the warm setting. The warm idle speed is well, slightly faster than what I feel is good, but it's not a V8 so I think it is OK. The mixture screw is turned clock wise until the warm idle speed started to go up and then I backed it off half a turn.

    All linkage on the left side of the carb moves freely. There's a little arm on the lower left side of the photo that if I move counter clockwise all the way will cause the engine to shudder and then stall.

    So... there you have it... why the stall out and no start on the highway!?
    David Marshall
    Quesnel, BC - Canada

    A Daihatsu HiJet, a couple of BMW adventure bikes and a bunch of 4WD Volkswagens!

    http://www.hasenwerk.ca

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