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u/LorenzoCM757

Image 1 — [Help] 125cc EFI 4-stroke (Honda CG) cranks but won’t start - flooded. Need advice.
Image 2 — [Help] 125cc EFI 4-stroke (Honda CG) cranks but won’t start - flooded. Need advice.
Image 3 — [Help] 125cc EFI 4-stroke (Honda CG) cranks but won’t start - flooded. Need advice.
▲ 2 r/Fixxit+2 crossposts

[Help] 125cc EFI 4-stroke (Honda CG) cranks but won’t start - flooded. Need advice.

Hi everyone, I’m building a go-kart using a 125cc EFI 4-stroke engine (Honda CG), not sure about the year. The engine cranks but refuses to start, and it seems to be severely flooding the cylinder with fuel.
The Setup & Mods:
• Custom 38mm straight-pipe exhaust (two bends, totally open).
• Custom air intake (two bends with a pod filter, no airbox).
• Fuel pressure set at a steady 2.8 - 2.9 bar.
The Symptoms:
• It used to start, but wouldn't hold idle for more than 10 seconds and bogged down hard on throttle.
• Now, after touching the air screw, it won't start at all. It just shoots grey smoke while cranking.
• The spark plug gets completely fouled and black.
• Crucial clue: I cleaned the spark plug, disconnected the fuel pump, and cranked it. It fired up and ran for 3 seconds just burning the leftover fuel in the cylinder. As soon as I plug the pump back in, it floods again and dies.
What I have already tested/ruled out:
• Spark: Good and strong.
• Injector: Tested it out of the manifold. It holds 2.9 bar perfectly and does NOT leak or drip when closed.
• TPS (Throttle Position Sensor): Tested with a multimeter. Resistance is smooth, no dead spots.
• IACV / IAT (2-wire sensor on throttle body): Cleaned.
• O2 Sensor: Tried starting with it both plugged and unplugged. No difference.
• Battery: Fully charged, tried two different ones.
• Safety switches/Killswitches: All good (starter engages fine).
• Air screw: Tried everything from 0.5 to 4 turns out.
My Theory:
Since this is a Speed-Density EFI system, I suspect my massive 38mm open exhaust and pod filter have killed all manifold vacuum. The MAP sensor is reading near atmospheric pressure at cranking/idle, thinking I'm at WOT, and telling the ECU to dump massive amounts of fuel, flooding the engine. I also haven't checked valve clearances yet (might be tight, losing vacuum).
Are there any workarounds (resistor on the IAT/ECT to lean it out, restricting the intake) or is checking the valves the absolute next step?
Also, when the engine was holding idle for 10 sec it didn’t have any exhaust pipe at all, then i touched that air screw and then thinking “no pipe” was the problem i built it.

Any input is highly appreciated!

u/LorenzoCM757 — 8 days ago
▲ 2 r/Heidenhain+2 crossposts

Heidenhain TNC 430 on Mecof: RS-422 and RS-232 comms issue [NO DIR] - Factory X22 port & X21 questions

Hello everyone,

I'm fighting with a data transfer issue on a Mecof milling machine equipped with a Heidenhain TNC 430 control. I am consistently getting a [NO DIR] error on the machine when trying to access the PC via RS-422 or RS-232 using both TNCserver and TNCremo.

Here are the technical details and what I have already tried. Any help from Heidenhain veterans would be hugely appreciated.

1. The Hardware Setup:

  • Machine: Mecof with Heidenhain LE 426/430.
  • PC 1: Desktop running Windows XP with a native, physical COM1 port.
  • PC 2: Laptop running Windows 11 with USB-to-RS232 adapters.
  • Converter: Sintechi RS-232 to RS-422/485 passive terminal block converter. It is externally powered with 12V DC.
  • Software: TNCserver / TNCremo.

2. The Port & Wiring (The Mystery):

  • Outside the electrical cabinet, there is a factory DB15 port labeled "Program Loading".
  • I traced this cable inside the cabinet: it is physically connected to the X22 port on the Heidenhain logic unit.
  • Electrical Verification: I measured the voltage on the DB15 pins while the machine was on. Between Pin 2 (GND) and Pin 4, I get 0.9V DC at rest. This confirms it is an active RS-422 differential line, not RS-232.
  • Pinout used on DB15: * Pin 2 = GND
    • Pin 3 = TX+
    • Pin 4 = TX-
    • Pin 5 = RX+
    • Pin 6 = RX-

3. What I have already tried (Troubleshooting):

  • Software Settings: PC set to LSV-2, 9600 Baud, 8-N-1. Machine MOD menu set to RS-422, LSV2, 9600 Baud.
  • Handshake: Set to SOFTWARE (Xon/Xoff) or NONE on the PC. (The machine MOD menu for RS-422 doesn't even show an handshake option).
  • Windows XP COM1: I disabled the FIFO buffers entirely in the advanced COM1 device manager settings.
  • Polarity Swapping: I swapped the TX+/TX- and RX+/RX- wires on the Sintechi converter to account for incorrect Chinese labeling. Still [NO DIR].
  • RS-232 attempt: I also tried connecting a custom Null-Modem cable (with 4-5 and 6-8-20 bridges) to the X21 port, but it didn't work either. Tried all baud rates, FE protocol, different parities, etc.

My questions for the experts:

  1. Since the factory "Program Loading" cable goes to X22, are the DB15 pins (2, 3, 4, 5, 6) exactly correct for the Heidenhain RS-422 TX/RX pairs on this specific port? Do I need to change a specific Machine Parameter (MP) to enable data transfer through X22?
  2. Right next to it, the X21 port is empty. Is X21 the actual RS-232 port? I tried connecting a standard Null-Modem cable (bridged 4-5 and 6-8-20) to X21, but got "Interface not ready" / no connection regardless of baud rate or FE/LSV2 protocols. If X21 is the 232, what is the exact trick/pinout to make it work?
  3. Has anyone successfully used one of these cheap active/passive Sintechi RS422 converters on a TNC 430?

Thanks in advance for your time!

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u/LorenzoCM757 — 11 days ago