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Troubleshooting 101

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  • Troubleshooting 101

    Here's a list of tips to try when your bike won't start, like in the spring.

    Help! It's spring time and my bike won't start!

    First, check the battery. Are the lights coming on? Are they strong? Is the starter motor enganging? Is it "clicking?" Obtain a Multi-Meter and test the battery. Is it reading 12-13v DC? If not... attach a battery tender OR attempt a jump start. To Jump start, get a car or truck with a 12v charging system. With the car or truck OFF attach jumper cables and attempt to start the bike.

    Charging system looks okay? What about fuel?
    Did you put stabilizer in the gas last fall? Turn the petcock to PRIME for 30-60 seconds to make sure you have gas in the bowls.
    You can check to be sure your bowls are filling by cracking the drain screws (with a rag under the carbs) to see that gas drips out.

    Still no luck? Huh? Time to dig in.

    From here, you can try a multitude of trouble shooting.
    Sparkplugs. Remove and inspect. Plugs should not be black, sooty, oily, or damaged.
    Coils. Check for spark. Be sure to use a good solid ground, laying the plug on the engine might note do it.
    All connections good?
    Wires. Wires aren't frayed or loose? Boots have good connections to plugs?
    Any questions about the plugs, install new ones.

    Petcock. Is it operating correctly? Flows fuel freely on prime?
    Airbox/Airfilter. Installed correctly and clean?

    Is it still too cold? Try heating the engine or the space the bike is in. But be careful of gas fumes!!

    If none of the above seem to be helping... then you likely have dirty carbs. If the bike will idle, but only with the choke on... the pilot circuit is dirty. Check out Carbs 101 and Carbs 102 in the wiki.

    Ugh... it's spewing gas everywhere! Out the puke tubes? Gas in the oil/crankcase? Check the petcock function. The diaphragm is probably bad and/or you have a stuck float. Sometimes to unstick a float, you can drain the bowl. Put a small container under the float bowl to catch the gas... and open the drain screw. Do this once or twice. This will usually flush sediment out.... but can be an indication of a bigger problem! Like rust/scale/dirt/junk in the tank.

    Hopefully others will come along and provide some additional sage advice. Please, don't post QUESTIONS here... post ANSWERS to problems.

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  • #2
    Originally posted by portetra000 View Post
    If i rev the engine quickly the rpm drops right to idle but if i ride at around 5,000rpm and then clutch in it will drop to 2500 for about 30 seconds and return to idle....sometimes haha. Carbs are all cleaned, floats are set to stock height, however for some reason my bike likes my a/f screws at 3 turns out . The engine is def noisy but then again ive been told that the valvetrain is louder than most bikes. But my biggest give away was when i bought the bike from an idiot before me i noticed that the boots on the air box were crispy and burned inside the box. Im thinking exhaust and intake valves open at the same time? maybe explaining ****ty performance/****ty idle/****ty noise. Thoughts? And just a heads up since im still tuning the carbs are only synched using a feeler gauge which isn't helping the fact that my bike doesnt like to idle below 1000rpm. After the valve adjustment i will be doing that with a manometer.

    Stock 1990 750
    stock filter
    stock jets/needles
    stock exhaust
    You have multiple issues, and this will cover fixing most of them.

    Pull the carbs and replace the engine boot orings if they are flat or deformed. Inpsect the boots as well, replace any that show signs of cracks. Set the a/f screws back to 2.5 turns out. (your gonna fix the problems that made it work better by running richer, so set them right now where they should be).

    Check all of the rubber caps on the carbs, and the petcock vacuum line is not damaged or have holes. Replace as nessasary if cracked or dry/hard.

    Remove the airbox boots, clean the airbox. Replace any damaged parts (You mentioned possible fire?) and use rubber gasket sealer to seal the boots and box. Inspect/replace the airfilter if dirty or damaged, or if it's not an OEM replacement filter or equivilent. K&N or aftermarket high flow filters will be a problem.

    Put the airbox back on the carbs before installing the carbs. Do this with the air filter out, so you can reach into the airbox and push each boot on and hold it while tightening the clamp down. Make sure it's fully seated and properly tight (don't over tighten or you cut the boots and cause vacuum leaks).

    Install the carbs (with airbox) and then use an alternate fuel source (gas tank off and out of the way) to start and run the bike.

    Pull each spark plug boot and double check the condition of the wires. If the last bit of the wires where the boots connect are hard, cut back to soft wire and screw the boots back on. Triple check the boots are pluged onto the right plugs for the correct cylinder (might want to check/replace your spark plugs if you dont' know their history_)

    Try to get the bike to run and idle at this point.

    In low light (if it's middle of the day, put a thick blanket or something over your head and the bike for a moment) and with the engine running check for any arcs to the engine from the plug wires and down in the plug wells from the plug boots. If you find arcs... fix them before going on.

    Next double check there are no vacuum leaks. You sealed off the petcock vacuum line for example right?... since it's not plugged onto the petcock? Use a spray like starter fluid in short, small, directed bursts around all rubber parts on the carbs and airbox/carb boots. If the rpms change, you have a leak that must be repaired.

    Once you know there are no vacuum leaks, sync the carbs fully with a manometer.

    At this point, you should be able to set the idle at 1100rpms +/-100 and blip the throttle and have it drop back and hold stead at 1100 with no issue. If it hangs at this point, you either.... did not correctly complete one of the steps above,, or.... your carbs were not properly cleaned.

    93 750 Kat

    Modified Swingarm, 5.5 GSXR Rear with 180/55 and 520 Chain, 750 to 600 Tail conversion, more to come. Long Term Project build thread

    "I've done this a thousand times before. What could possibly go wron.... Ooops!"


    • #3
      nice information guys
      thread is my issue problem guys

      nice information guys
      thread is my issue problem guys
      Last edited by pallmania23; 03-18-2015, 09:09 AM. Reason: Automerged Doublepost