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Broke down today, possible causes?

Discussion in 'Mechanical & Technical' started by zxrod, Jul 5, 2014.

  1. I guess I'll preface this by saying this is my first year riding and I'm not particularly mechanically inclined but I'm trying, so bear with me.

    I've got a ~15 year old Nighthawk 750 with about 13k miles that I've been tooling around on that crapped out on me and I'm trying to figure out why. As I was getting on the on ramp of the highway and up to speed suddenly the oil light turned on, the throttle became unresponsive and the bike choked out. After walking my bike back up the on ramp and onto the sidewalk I really flexed my mechanical skills and switched to the reserve tank in case I somehow burned the main tank in only 100 miles. Still wouldn't start.

    After that I pulled off the side and checked my air filter that I changed last week, not because I thought it would do anything but because it's the only part I've ever changed myself (last week) and maybe I did something wrong? After putting the side back on I decided to try and fire it up again, gave it lots of choke and throttle and somehow she came back to life. I let it warm up for a few minutes and then rode the 5 mins or so back home without issue.

    I guess I'm wondering if anyone has any idea what the problem could have been? I don't think my fiddling with the air filter accomplished anything. It was probably 20-30 mins between when it died on me and I got it started again. Would the bike not being warmed up enough before trying to get up to that speed cause this or is it indicative of a bigger problem? I ride it pretty frequently around the city without any problems but not on the highway often.
  2. Be very concerned that the oil light came on. Check your oil level before anything. Is it possible you might have bumped the kill switch to OFF?

  3. On a bike that old it could be many things.
    I would start with a new spark plug and checking/cleaning all of the electrical connections.
    Some electrical parts will fail when they get hot and then work again when they cool a little, so they can be hard to diagnose.
    Crud in the carb could also cause those symptoms. If there's a drain bolt on the bottom of the carb, remove it and spray a little carb cleaner up into the bowl.

    Did the oil light come on before the engine died? or at the same time?
    Last edited: Jul 5, 2014
  4. The oil light came on right when it died. We changed the oil like 2 months ago and I just checked it and it was looking pretty dry. Is it possible/likely the bike burned off the oil that fast? I would have noticed if it was leaking oil in my garage. If it choked out on me because it was dry on oil is it likely I royally fucked the bike up in doing so?
  5. Sounds like you ran out of gas.

    You switched to reserve but didn't wait long enough for the carbs to refill.

    On some bikes it's not instantaneous for the float bowls to refill.

    Other than that, it's difficult to diagnose without more info about the bike, how long you've had it, and the condition it was in before you got.

  6. It might be that simple. Many bikes have a vacuum operated petcock. If you run the carb dry, it might takes 5-10 seconds of cranking to refill before the engine will start.

    You could start the bike on reserve, then switch to ON while it's running. If the bike dies after 3-5 min, you'll have your answer. You ran out of gas.
    And see if the oil light comes on as it dies, this could be normal for that bike.
  7. KevinD

    KevinD Modulator Staff Member


    Or even simpler, just buy gas, and if it takes a tankful (you do know how much a tankful is, right?) then you know what happened.

  8. You would not have burned through much oil in just a couple months riding under normal conditions, still it never hurts to check your levels.
    If your bike felt like it was bogging down it very well could be crud in your carbs.
    Those would need to be cleaned out but the real question is why you have crud in your carbs. Petcocks have seals in them that degrade over time and sometimes put bits if rubber in your fuel system causing clogged carbs.
    You might want to look up an internet forum for nighthawk owners and run your questions past riders with your bike.

    Sent from my MB865 using Ohub Campfire mobile app
  9. My best suggestion: go to and ask this question.

    It's populated by a bunch of Nighthawk riders with lots of knowledge about known problems with specific NH models.
  10. Be sure when you checik your oil level you follow the instructions for YOUR motorcycle. I have found bikes that the owner filled the oil to the TOP of the fill hole--WRONG--. If you are checking it on the sidestand you are probably not doing it correctly. I agree with the possible running out of gas scenario and vacuum operated petcocks. I always set my trip odometer when I fill with gas so I have an indicator to go by for when I need to get gas again.
  11. Thanks for all the tips guys. If it turns out I just ran out of gas I'll never have been so happy to be "that guy".

    I think that was the case yesterday. I was so panicked by the oil light coming on that I checked it in a rush.

    Thanks for the heads up on the nighthawk forum, that might be a valuable resource in the future.
  12. So yes, this is the part that's confusing me a little bit. I know that according to my manual the tank holds 4.76 gal (.79 in reserve). In the past I would fill up after around ~150 miles and that would typically be 3.5-.375 gals I'm putting in. When it crapped out on me I was sitting at 100 miles on that tank. I'm far from an aggressive rider but I recently moved deeper into the city so much more of my riding has been city riding. Is it likely that the city riding hurt my gas mileage that much?

    Here's a dumb question that I think I know the answer to but might as well ask it while I'm on a roll. When I refill the main tank it refills the reserve too right? It was my general understanding that when you turn the petcock it's just opening a valve located lower in the same tank right?
  13. The vent on the gas cap can cause problems with vapor lock. Don't want to hear whoosing sound when the cap is popped open. You didn't pinch a fuel line when fussing with air box?
  14. I recently sold my 2003 NH 750 after owning it for 2 years, and based on my experience, I think it's unlikely that city riding would knock that much off your gas mileage. Not impossible, but unlikely. My riding was mostly city, with the occasional longer highway jaunt, and I was putting in ~3 gallons at the ~130-mile mark.

    Have you ever had the carbs cleaned and synced?

    You're right.
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