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Some Thoughts on Carburetors

Discussion in 'Tips and Tricks' started by Jigs-n-fixtures, May 15, 2020.

  1. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    Every body seems to hate the stock carbs, and I’ll admit that the one on my Hijet took a bit of figuring out, and at the time nobody had a rebuild kit.

    Look at G&R Imports Maintenance Tips Page, https://www.grimports.com/maintenance-tips

    G&R’s tips is a great starting point. The other thing I’ve noticed is that most mechanics who started working on cars after the 70s when the emissions carbs arrived don’t seem to have a skill set to deal with carbs.

    So here goes:

    The chokes on all the tiny trucks seem to be wet, or heated by the water. If your having problems with the choke, check the other things on the G&R list, before you blame the carb, and start tweaking on it. There is an order to troubleshooting. Needlessly, tweaking on the carb, can make things worse, and harder to track down the actual issues.

    Make sure the vacuum lines are hooked up correctly and not cracked or leaking. Carbs work on vacuum signals. And, so does the emissions system. If the vacuum lines are messed up, neither the emissions system, and the carb won’t work right.

    When you disassemble the carb bottom out all the adjustments before you take things apart. That way you can put things back to where they were as a starting point. Be careful disassembling the choke, back everything off, and be sure to note how wound up the springs are. The spring controls the tension on the choke blade.

    Set the initial choke setting using the indexes on teh mechanism as a starting point.

    With the carb torn down. Use the little straw on the carb cleaner, and blow carb cleaner through every passage, from both directions. Clean things up as well as you can. Use a firm toothbrush to scrub stuff.

    When rebuilding, with the carburetor inverted the top of the float should be parallel to the body of the carb.

    Once you have it back together get it mounted, and get the vacuum lines routed correctly. Then set the idle a little higher than it was before you try starting.

    Once you have it running, and warmed up. Double check the timing.

    The thing most people can’t do is set the best lean idle. What you do is adjust the idle fuel mixture as lean as you can with the engine running smoothly.
    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 you can adjust the idle speed back to whatever the manual says it is supposed be. Go ahead and do the rest of a tune up. The next morning when the truck is cooled off, adjust the high idle. There probably isn’t a high idle listed in the manual. Just set it at 300 to 400-rpm above the normal idle.
    Limestone likes this.
  2. Limestone

    Limestone Well-Known Member

    Very Educational! I like it! I still have my old carb. just in case I can find a two wire solenoid for it! That's all it needs! My uni was almost 30 yrs' old when I inherited it. I know it sat for about 10 yrs. before I got it, before that, it ran for about 20 yrs.! I somehow can't find fault with that! Great post, Thanks!
  3. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    Limestone, so far as the solenoid: I think that it is the one for the speed limiter, you could just clip it back, and install it, or just put in a plug and eliminate it all together. It pulses into the main jet when the speed limiter kicks in, and If your not trying to use the speed limiter it is kind of superfluous.

    And, the other possible solenoid is the idle cut, and the purpose it serves is to keep the engine from running on when you shut it off. And, you have a manual transmission, so all you need to do is feathery the clutch as you shut down, and that problems solved.
    Limestone likes this.
  4. Limestone

    Limestone Well-Known Member

    I did not realize that! I think a plug is the solution, because the can part of the solenoid has a split in the metal, and leaks fuel. I did think about trying to braze or silver solder it, but instead, I went with a new after market carb. and a manual choke!
  5. werase643

    werase643 Member

    my pull my head out of my ass moment today..... if you convert to a bike carb..... use a bike fuel pump...... either the vacuum operated or the electric... it only runs when the float is open.... pretty kewl actually.... prevents from having to get the 4-7 psi aftermarket pump down to 1-2 psi and it cycles as the float bowl needs it.....

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