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No top-end power when it's cold outside

Discussion in 'Honda Acty' started by ErikAlexandre, Dec 9, 2021.

  1. ErikAlexandre

    ErikAlexandre New Member

    Hi everybody. My truck has a strange problem that when it is cold outside, it lacks power and can barely get to 80km/h going down a hill, when in summer I get 110km/h, see video taken at -5°C:

    Here is what I already did look up:

    - Changed spark plugs with NGK BKR6E-11, see pic attached of a ~3000km plug.

    - Changed air filter.

    - Spark plug wires were changed before I imported the truck, they seem in great shape.

    - Cap and distributor were changed before I got the Acty, but I opened it and cleaned it well. Contact points look good and not worn.

    - Compression is 185psi – 180psi – 180psi.

    - The truck runs the same without the air filter and cover, only louder but no more power.

    - Fuel filter has been changed for a Wix 33203.

    - 87 or 91 octane makes no difference.

    - Throttle cable has been readjusted the remove as much slack as possible.

    - Air vent valve solenoid and fuel cutoff valve solenoid were removed from the carburetor and they move freely when 12V is applied.

    - The entire carburetor has been took apart to clean the jets, the float and needle, the accelerator valve, the power valve, and the choke pull-off. Everything is working as it should and nothing seemed gunked.

    - All vacuum lines were checked for cracks and are OK. No idle speed change when sprayed with brake cleaner.

    - Cleaned the EGR valve.

    - Cleaned the PCV valve. The vacuum port was completely blocked with gunked oil.

    Now for what I don’t know how to test or don’t know how it works:

    - I’ve looked at both thermovalves on the intake to see if they are working correctly. The one on the left side of the truck (3 vacuum hoses) has vacuum on the top one, but nothing on both horizontal ones, truck hot or cold. The one on the right side (2 hoses) has nothing on both, hot or cold.

    - The choke wax cylinder thingy doesn’t seem to do anything. I checked the linkage with the truck cold and then at working temperature, and nothing moved, even if I rev it. When I look inside the carb, the choke plate is horizontal, so that means the choke is off, right? I never had any trouble with starting my truck.

    Otherwise, I’m out of ideas, anyone ever had the same problem or could point me to other directions?

    Attached Files:

  2. ErikAlexandre

    ErikAlexandre New Member

    Usefull information I forgot to add: 1994 Honda Acty SDX AWD, no ac, vin HA4-2105625

    Today I removed both thermovalve from the intake to test them in boiling water. The right one (2 hoses) opened up and allowed vacuum, so it's fair to say it's alright. When I tested the left one (3 hoses), It didn't open when I blew/suck air from the top barb, so it became my main suspect. I broke one of the barb during reinstallation, so had to order a new one anyway, I also got both carb solenoids, just in case. I will update when I get the parts from Japan, I plan to open the distributor to see if the Vacuum Advance works, since one of the hoses on the thermovalve is to open it. Until then, other ideas of things to validate are welcome.

  3. Acerguy

    Acerguy Moderator Staff Member

    Does it start normally even when cold? Have you checked the fuel pressure?
  4. ErikAlexandre

    ErikAlexandre New Member

    Yes it starts fine, whether the truck is cold or hot, or even hot or cold outside, two pedal push and it always starts right up. It also idles really nice, no smoke or anything.

    As for the fuel pressure, I did not think about that. Do you know what kind of pressure in PSI the pump is supposed to make?
  5. Acerguy

    Acerguy Moderator Staff Member

    Well, if it's starting fine, I would not suspect the fuel pressure...but then, I'm far from an expert. Besides, I just realized that your truck is not fuel injected is it? Sorry to misdirect. I'm in the dark on carbs. (For reference for others, my Hijet recently started starting hard but would run normally once warmed up...sort of the opposite of what you're having. I checked the fuel pressure near the injectors and it was only about 12psi. I replaced the fuel pressure regulator (from a circa 2000 Corolla) and it's back to over 40psi and the problem seems to be resolved.) Best of luck!
  6. ErikAlexandre

    ErikAlexandre New Member

    Yeah, I think that carbureted engine fuel pumps are supposed to run at like 5-6 PSI. I know the carb is getting fuel since it starts and runs well at slower speeds. I will be reopening the carb this week, since I have it out while I wait for my solenoids, to see if I missed anything obvious. Thanks for your help, I would love to have a Fuel Injected truck like yours instead of a carb one!
  7. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    The fuel pressure for carb on these trucks needs to be around 2 to 2.5-psi. Much more than that and the fuel will go right past the needle valve and flood he truck. There have been guys on here who have had fuel coming out of the overflow of the bowl and straight into the Venturi of the carb.
  8. Greg Szymanski

    Greg Szymanski New Member

    did you ever fix this issue?
  9. ErikAlexandre

    ErikAlexandre New Member

    Yes, I changed the spark plugs to recommended BKR-6E and I also changed the spark plug wire while doing it. It didn't improve power overall, so I ordered both carb solenoids and the vaccum valve that is on the coolant port of the intake. It did made a difference, I can now go about 100-105Km/h, so it is definitely an improvement.
    installater and shogun like this.

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