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Bike idles only on choke, dies when throttled the slightest amount

Discussion in 'The Garage' started by rockinjon, Jun 30, 2016.

  1. rockinjon

    rockinjon XS400 New Member

    Hey guys, here's one for ya:
    My bike quit running and I traced the issue to a bad TCI box. (I've gone through 3 of them in the last year!!!)
    I found a used one on ebay, and plugged it in, and it started. I gave it throttle, and it died. Restarted it, let it idle, and tried giving it throttle again, and it died once more. It kept dying each time no matter what. I though the carbs must dirty, so I completely disassembled them, and carb dipped all the parts (sans rubber ones) (let them sit for a several hours each), blew out the holes with carb cleaner, and re assembled them.

    Put them back on, and there was no change. The tiniest bit of throttle and it dies. But I also noticed my petcock is leaking too. So I took that apart and inspected it, but there are no tears in the diaphragm. I thought if it was a vaccuum issue, running it on PRIME would bypass that just to see if it would rev up, right? It does the same thing no matter what setting. I know it's getting plenty of fuel, and both cylinders are sparking. They aren't super bright sparks though... Could that new TCI be "weak" or something? Coils going bad? I doubt it's a carb issue as they are both clean enough, and the petcock on PRIME should be dumping fuel in there even if it's a petcock issue... any ideas?

    Thanks for the help guys!
  2. 16VGTIDave

    16VGTIDave XS400 Guru Top Contributor

    It sounds like your bike has multiple issues. If your bike is killing TCI modules, you need to resolve that first before you need another. You may already be there, but try other fixes first. Clean all the electrical grounds and connectors. Check the coils per the manual and replace the wires and spark plug boots. Also, don't EVER crank or run the engine with the plug wires disconnected. Even one failed spark could feed back and fry the module.

    That said, it sounds like the carbs are still dirty. Specifically the Pilot circuit and its ports. That is the only thing that makes any sense to me based on your description. The throttle and TCI module don't interact other than the module changing the advance based on engine RPM.

    Let us know what you find!
  3. indio129

    indio129 XS400 Member

    I had the same issue. I cleaned the carb and it didn't help. Then I discovered that the carb needle was broken. They are rubber tipped held on with glue. So when I throttled, the tip of the needle would stay in the idle position. I'm not sure if that's your problem, but might be a start.
  4. How did you make out on this?
  5. rockinjon

    rockinjon XS400 New Member

    Thanks guys, I have been busy and haven't had time to rip into it again. I will give the forum an update after I get a chance. God damn I hate ripping that carb rack out and wrestling with it trying to put it back in... Tempted to go the pod route... But then I imagine it would introduce a whole nother mess of tweaking issues...Jet sizes, etc... ugh why didn't I just buy a fuel injected bike. 2 summers in a row I've missed out riding because this piece of shit won't run right....
  6. Taylor Davy

    Taylor Davy XS400 New Member

    (Thread revival) I am having a very similar issue with my bike, starts with full choke, if I release the choke slightly or touch the throttle, the bike dies. Did you resolve this issue? I am rebuilding and cleaning the carbs out now, and I am going to check that all the paths are clean as can be. Was that the issue you had? a plugged pilot issue like someone mentioned before?

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