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Loss of power at full throttle

Discussion in 'Honda Acty' started by deB, Apr 13, 2022.

  1. deB

    deB New Member

    1996 Acty Town in excellent condition and 34k Km.
    -Starts nearly instantly and runs incredible with part throttle, enough power to take off in second with ease and climbs steep hills like a goat.
    -If you press the accelerator over 50% the engine loses power bogging and even sputtering some times.
    -Let up on throttle and she's off and running again like nothing ever happened.
    -Will accelerate to redline at partial throttle.

    Removing the airbox cover does nothing but make it louder.
    It has a brand new air solenoid.
    Fresh fuel.

    Aside from throwing a bunch of the usual suspect parts at it what guidance can you all offer to help focus my
    troubleshooting efforts.

    Thank you in advance.
    deb
     
  2. VanOne

    VanOne Member

    Wrong mixture or wrong sized pilot jet for the altitude.
     
  3. shogun

    shogun Active Member

    check the solenoid p/n you changed, there are actually 2 solenoids at the carb https://minitrucktalk.com/threads/1995-ha4-only-runs-without-airbox-cover-running-rich.21981/
    Acty Air Vent Cut Solenoid Acty HA3.HA4 16031-PZ3-000
    Acty Carburetor Fuel Cutoff Valve 16024-PZ3-000

    The vent solenoid is a very common failure element, if yours hasn't failed yet, it will. When I had the problem and asked a friend who runs a minitruck repair shop, he immy pointed that out.
    Also typical symptoms are high or too low idle, black smoke, an indication that your air-fuel mixture is running rich.
     
  4. deB

    deB New Member

    The fuel cut solenoid I tested successfully, the air vent I was unable to determine its function without removing it so I simply ordered a new replacement. Upon installation of the new unit I bench tested the old one and it works fine.
    Rebuilding the carb was my first inclination as the truck has such low mileage it may have some varnish deposits in the jetting and bleed passages.
    I will re-check the fuel cut solenoid at that time.

    If I get any progress prior to arrival of the kit I will be sure to update this thread.

    Thanks to all who have contributed and viewed alike.
     
  5. in line fuel filter is where I would start, then jump to cleaning and adjusting carb.
     
  6. deB

    deB New Member

    Amayama got more of my money this morning!
    Added the filter to the list. Thank you Jonathan.
     
  7. rkasc4

    rkasc4 New Member

    Marco, who does the YouTube videos, says he had the same problem and he did the plugs, plug leads, both solenoids etc. and it was still the same. He swapped out the ignition module and that fixed it.

    Mine has the same problem and it's had new plugs and leads. It's going into the garage to have both solenoids and the ignition module changed. Wish me luck!
     
  8. deB

    deB New Member

    After changing every consumable at my truck (plugs, cables, ignitor, cap/rotor, solenoids, all the filters, timing belt, vacuum switch, hoses) the issue continued to present itself.

    When I pulled the carb and cleaned it out the primary jet was frozen in place from varnish, it was my first inclination and it proved to be correct. Amayama has the carb and spacer gaskets, the primary and secondary jets available and it's less than $30 for all of them. This was the single process that fixed my issue as I went part by part and system by system to find it. Happy that the truck now has a documented service baseline now, but servicing the carburetor first would have fixed the problem I was experiencing. It is an easy repair to undertake, a little messy from spilled coolant and fuel but a 14mm wrench, JIS phillips #2 screwdriver, picks, carb brushes and Berrymans carb cleaner are all I needed. Remove the carb (take pictures of each vacuum line before you remove them to aid in reinstallation), disassemble the carb slowly and lay the pieces out in the order removed (an old egg carton can help keep you organized here), remove everything that has a screw head or a wrench flat there are a couple of tiny hidden o-rings (look at the Amayama diagram if you don't have a manual), now investigate every little hole/port/orifice with the straw on the carb cleaner, then do it again and use the brushes if necessary to dislodge crud, reassemble, reinstall, enjoy a truck with accurate throttle response.

    The fact that the solenoids are brought up as the problem 9 out of 10 threads illustrates that they frequently can fail, and in a new to you truck they are a good idea to replace upon arrival. That said, the carburetor is nearing 30yrs old in many of these trucks and the reality is they are dirty and varnished and causing issues for many.

    I wish you best of luck in your repair adventure.
     
    installater and rkasc4 like this.
  9. rkasc4

    rkasc4 New Member

    Thanks for all that info you've given me, I'll take that to the garage with me as well. Thanks!
     
  10. Robert Orr

    Robert Orr New Member

    Hello Deb,
    Have you fixed your over 50% throttle issue? I have the same issue. It runs great - until you get it over 1/3 to 1/2 throttle, then if falls flat. I had to replace the carburetor for a different issue, but it exhibited this issue with both the old and new carburetors (no change at all). I've checked timing, it makes no difference if the air box is off or not, the choke is not closing and I've noticed it spits fuel back out the carburetor while it's exhibiting this issue (with the air box removed).

    Just curious if you've fixed it yet.

    Sincerely,
    Robert
     
  11. deB

    deB New Member

    Robert, in short yes I found the solution and it had nothing to do with solenoids at all.
    The primary jet gets frozen from varnish and the pintle valve on the spring cannot move as it needs to and the others are certainly filthy. Rebuild the carb yourself, it's cheaper than a rebuild and easier than you might think.
    I sold my truck as we moved to a smaller property and didn't need it anymore. However I still have another set of jets and rebuild gasket kit I can send if you are interested lets take that conversation to private messages.

    Reference this image from Ayama. E-1 carburetor for Honda Acty Truck frame M-HA4 - Amayama Parts-29,28,18,3,1
     
  12. MrJPolito

    MrJPolito Active Member

    Another point of failure here that may be relevant is the fuel pump. My friend's Subaru Baja just had these same issues (starts off fine, but fails to accelerate if you gas it too hard, struggling to get around in general) and we replaced her fuel pump and the problem was instantly gone. I guess these symptoms generally point to the fuel system anyway, so fuel pump, filter, and carb are all things to check.
     

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