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Easy DIY carb balancer

Discussion in 'Tool Corner' started by Tom W, May 15, 2017.

  1. Tom W

    Tom W Member

    I made this this weekend, mainly for balancing triple Webers but it also worked a treat on my TC (better than the Webers infact). I'm too tight to buy the correct kit, so decided I'd get a bit resourceful.

    All from bits and pieces that are readily available from the hardware store and the motor factors. Carburettor balancing meets school boy science.

    IMG_0001.JPG IMG_0003.JPG IMG_0002.JPG

    I've already posted in my 4cyl engine post, but thought it might get more coverage here. If any one wants to copy it or know how it works, let me know and I'll take more photos and add more details.
    Willy Eckerslyke and sdibbers like this.
  2. ButterFingers

    ButterFingers Member

    now that is a clever piece of the mother of invention, the need arises and the brain starts to grind into action.
    I would love to know more about it Tom, please post some more information for us all..
  3. Tom W

    Tom W Member

    No problem. Here's a shopping list of what you need.

    1x piece of wood. It needs to be about 2.5 to 3ft long.
    1 length of washer tube. The tube I bought was about 5mm dia. It needs to be twice as long as the timber, plus enough spare to reach from where you'll stand the manometer to to the carb mouths without pulling too tight. The length I bough was about 8ft.
    P clips and screws or cable clips to secure the tube to the timber.
    1 x rubber plumbing reducer bung. This should fit across the carb intake and make a good seal.
    1 x plumbing plastic cap sized to fit in the bung.
    1 x 12mm plastic hose connector
    1 x 5mm plastic hose connector
    1 x mig welding tip
    ATF/PAS fluid.

    Cut one of the tapered ends off the 5mm plastic connector. Drill a hole in the side of the 12mm plastic connector so the cut end of the 5mm connector will push in. This needs to be a tight fit, glue in place if it's loose. The small connector should protrude into the large connector so it creates a Venturi. See the 3rd photo in the above post. Drill a hole in the plastic bung to take the 12mm hose connector. Glue the connector into the bung. Add the rubber bung to the assembly to complete the carb adaptor.

    Clip the tube to the timber in a u shape. You want the two vertical elements side by side so you can compare the levels. Line up one end of the tube with the top of the wood. The other should be left long to reach to the carbs. Add the ATF to the tube. When it's settled it should be about half full. The exact level isn't important. Fit the newly made carb adapter to the long end of the tube. Add the mig tip to the short end of the tube. This slows the flow slightly and provides a more stable reading.

    That's the basic construction done. I'm going to upgrade mine slightly by adding some silver tape begind the tubes to make the reading easier, and use a bulldog clip to mark the level in use. I'll also add more wood to the stand skit stands up, and add a hook so I can hang it on the wall. (It should be noted, I don't know how washer tubing stands up to ATF. Don't stand it over something valuable in case it dissolves it and leaks out.)

    To use. (Variable Venturi carbs)

    1. Check everything is good on your engine. Even compressions, good ignition system, timing set correctly, valve clearances set correctly, carbs in good condition, no intake leaks etc.

    2. Set the mixture screws to the book value. Check these are even by removing the pistons and measuring the drop from the bridge with a vernier. Adjust to match.

    3. Set the idle speed by ear. You should start with each screw just making contact and wind them in the same amount from there. This should get you close to being balanced.

    4. With the airbox removed, measure the flow through each carb with the manometer. Hold the adapter over the intake, ensuring you get a good seal. The Venturi in the adapter creates a depression in the manometer. There shouldn't be any flow through the manometer so the engine shouldn't ingest the atf. The adaptor shouldn't restrict the intake, so shouldn't change how the engine runs. Wait for the level to stabilise in the manometer and note the reading.

    5. Switch to the 2nd carb and note the level.

    6. Return to whichever carb is lower and mark the level, either with pencil on the wood or a bulldog clip.

    7. Move to the high flowing carb and reduce the flow until it matches the low carb.

    8. Move back to the first carb to check they're still matched. Adjust to suit.

    9. If your idle speed is now too low, bring both carbs up together, using the manometer to check they still match.

    10. Now repeat the process to balance the choke linkage.

    11. Reassemble the airbox and go for a test drive, hopefully enjoying the benefits of synchronised carburettors.

    Hope that all makes sense.

    Willy Eckerslyke likes this.
  4. ButterFingers

    ButterFingers Member

    thank you Tom for the instructions, I have printed them , laminated, and now in my shed for construction...:)
  5. Tom W

    Tom W Member

    Be sure to have the workshop manual on hand too. It has all the details of setting the throttle linkage correctly after balancing the carbs, which I didn't cover in my list. The carb linkage should be disconnected whilst the carbs are balanced.

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