Engine backfires, won't start after jet kit installation!
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Engine backfires, won't start after jet kit installation!

This is a discussion on Engine backfires, won't start after jet kit installation! within the Technical forums, part of the Caferacer.net Forums category; I have a 1992 Honda Nighthawk 750 project. I'm trying to run straight through exhaust and pod filters. So I put in 125 mains, 40 ...

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  1. #1
    Junior Member kbwill's Avatar
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    Engine backfires, won't start after jet kit installation!

    I have a 1992 Honda Nighthawk 750 project. I'm trying to run straight through exhaust and pod filters. So I put in 125 mains, 40 pilots and 2 shims. After putting everything back together on the bike, it turns over, but backfires through the exhaust and the carbs. It does not start. Fuel is new. Any advice...besides the typical 'put the airbox back on'?

    It definitely flooded the first time I tried to start it. I cleared it and dried the (new) spark plugs and... same result.

    What am I missing here?

  2. #2
    Senior Member Dean's Avatar
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    Quote Originally Posted by kbwill View Post
    Any advice...besides the typical 'put the airbox back on'?
    When you put the airbox back on, don't forget to put the mufflers back on too

  3. #3
    Senior Member Geeto67's Avatar
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    Quote Originally Posted by kbwill View Post

    What am I missing here?
    Common sense, a scientific approach, thinking like a mechanic.

    Here is what you do. Put everything back to the way it was stock. Perform tune up procedure including carb sync and valve adjustment. Start bike and verify everything works as it should. Then remove mufflers. Run the bike and do a plug chop to see if the bike needs more fuel or not. Then walk over to your neighbors and ask him if the noise is tolerable. If he punches you in the face put the mufflers back on. If not then jet accordingly by going up size by size until the bike is no longer lean/rich. Then remove airbox. Take pod filter in hand. Ask yourself "did I buy shitty cheap used pod because I am not smart enough to google pod filter before hand?". Look at box, does it say EMGO, Dixie, or tucker rockey on it? Does it say anything other than Uni or k&n? If so throw in trash. Look inside pod and see if there is an internal ledge that actually shrinks the opening down? If so throw in trash. Buy new filters from k&n or Uni, spend more than $8 on them. Spend real money. Learn lesson about parts selection. Install new better filters. Start plug chop. Keep increasing in size until lean/rich condition goes away. Realize a month later that you are not smarter than a Honda engineer and you don't like people hating you and put mufflers and airbox back on.

    any schmuck can buy a kit and be a parts changer. Being a real mechanic requires you to think and diagnose. Your carbs are actually weather measuring devices and as such are sensitive to the atmospheric conditions dspicific to your locale. Sometimes jet "kits" work and sometimes they do not, it all depends on how lucky you are. Advice on what sizes to use over the Internet is useless and not a substitute for actual carb tuning skills.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
    - Samuel Beckett
    A tool is just an opportunity with a handle
    - Kevin Kelly

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  5. #4
    Senior Member ILoveThumpers's Avatar
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    Don't forget to put a screwdriver (preferably JIS) into a butane flame long enough to get it red hot, then jam it directly in your eye.

    That will give you an idea of how painful it will be to get your motor to run well by throwing parts at it.

    -Deek

  6. #5
    Administrator ffarl's Avatar
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    Change one thing at a time homie. Even if you want to go against everything these guys tell you, don't do it all at once, or you'll have no idea what's causing your problem. The best advice is usually the stuff you don't like hearing, and this thread is a great example of that.

    A word about running straight pipes: I'm going to assume you're in your early 20's, maybe even late teens. There was a time in my life when I thought I could get away with anything, when it came to the way I treat my body, so I get it. Never mind the fact that your neighbors will hate you. Never mind the fact that you'll be missing valuable sonic information both from the environment and your bike (Like how your motor is running or if a wheel bearing is about to fail), and never mind that you're making riders in general look like assholes who don't care about anyone else. Think about your ears man!

  7. #6
    Senior Member Geeto67's Avatar
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    I don't think this dude is coming back.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
    - Samuel Beckett
    A tool is just an opportunity with a handle
    - Kevin Kelly

  8. #7
    Senior Member Old Nail's Avatar
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    When I hear and read about people modifying intakes,carbs,exhausts,etc. it makes me wonder if and/or how much scientific research is done by aftermarket companies. An example of this, is Vance and Hines. Terry and Byron actually bench flow tested their products,and were one of the first to do this and the results showed in their work. They took the early gs Suzuki's to a status that we still see today. That is only one example and I'm sure there are many. There have been a few times when I've been given the pipes at a stoplight by some hacks that do not realize the difference between symbolism and substance. I will continue to reach down and disconnect the#1 spark plug wire just before the light turns green , and leave them sitting there with wide eyes and slack jaw as I launch when the light turns green and I'm gone. Most of those fools turn off somewhere and won't even speak to you at the next light.

  9. #8
    Senior Member ILoveThumpers's Avatar
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    Quote Originally Posted by Old Nail View Post
    ...reach down and disconnect the#1 spark plug wire just before the light turns green...
    That's worse than the kill switch. You're hardcore!

    -Deek

  10. #9
    Junior Member kbwill's Avatar
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    Hahaha you guys are harsh! I'm going to get it running well, don't you fret. I'm going to mess with the carbs tonight. If the exhaust is too loud, I'll change it. Maybe it will be, but I don't see a lot of difference between that and drag pipes. Neighbors are not that close anyway. I'm not a kid, just a guy with a garage and a dream. Thanks for the constructive feedback!

  11. #10
    Senior Member roccitycafe's Avatar
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    i think you're ignoring the sage wisdom in this thread.

    the question really is what is your goal, if your goal is to get it running well, and I'm assuming, fast, then yeah, put everything back the way it was and do a proper tune up, ride it until you're familiar with how fast it goes and where it makes power and doesn't. change one thing, if it improves, continue to tweak until it stops improving. move on to the next part, keep doing that until you run out of things to do to make it faster (you never do really, that's the fun). believe me, you're about the 20,000'th person to log on here and ask for jet sizes for open exhaust and pods, and it always begs the question, why do you think honda built the bike with an airbox and muffler? because the engineers there were knuckledragging cro-magnon? nope, it was cause it worked very well, and trust me, no shitty pods are going to work better than a large cavity of air and properly designed intake stacks. how many motogp bikes do you see with pods and open exhaust? do you think rossi would be just a bit faster if he hacksawed his exhaust and threw some pods on that bike? don't you think most of the people on here have tried the open exhaust and pods before? we're not coming down on them because we're grumpy. well, we are, but that's not the reason. anyway, maybe you'll take the advice, maybe you won't, just hope you don't get dusted by a 400f with airbox and muffler, that would just be plain embarassing

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