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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; As mentioned , your pod filters may be blocking the air jet port and " low pressure" slide port due the rubber shoulder inside them. ...

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  1. #21
    Senior Member Dean's Avatar
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    As mentioned , your pod filters may be blocking the air jet port and " low pressure" slide port due the rubber shoulder inside them.


    In the image below look at carb #1. The red ring represents the stock rubber carb to airbox boot. The stock boots are velocity stacks by the way , your pods are not. The green arrow points to your air jet port. The yellow arrow points to the "low pressure" lift port. Notice how the stock boot mounts around the intake and the ports are open to airflow.

    In the image below, carb 2 has the air jet port partially obstructed and the top port partially blocked. Carb 3 shows both ports fully obstructed/ blocked.

    Filter pods not only lack laminar flow from an air plenum (airbox ) via velocity stacks (stock boots) , pods can partially or completely obstruct/ block air ports resulting in lack of air to the jets and failure for the slides to lift properly. ( or in some cases at all )

    Keeping the stock airbox boots ( velocity stacks ) and sizing pods large enough to mount over them, helps. ( If you have sufficient exhaust , yes, mufflers and with proper jetting - meaning a/f confirmed at all throttle positons via dyno runs, o2 sensor, plug chops etc.) In my opinion, Uni filters are best because they have an open end and allow for more uniform laminar flow ( K&Ns are great filters, however the cap on the end limits laminar flow). However as kenessex stated, you will still have flat spot issues. DOHC fours with CV carbs absolutely hate pods.


    All that being said, listen to everyone that recommends you back up, install the complete stock air box / muffler systems, perform all tolerance checks, settings, tune and when you have a perfect running bike again. then STOP

    .. or if you are ambitious and very patient, proceed with one thing at a time, however if you proceed no mufflers and shitty pods, you would be wasting everyone's time.
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  2. #22
    Junior Member kbwill's Avatar
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    I put the stock jets and airbox back on. As for the exhaust, it's going to be unbaffled (for now) because the baffles are gone. Because I can't restrict the exhaust, I left one needle shim in; thinking this would richen it a little to compensate. Still having the same issues. I reversed the spark plug cables thinking I had mislabeled them...same result. At this point, I could care less about the pods, the airbox doesn't look that bad anyway.
    Last edited by kbwill; 04-13-2014 at 09:05 PM.

  3. #23
    Senior Member Harvey's Avatar
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    Did you check for spark on all cylinders? or just one?

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  5. #24
    Senior Member Dean's Avatar
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    Quote Originally Posted by kbwill View Post
    I reversed the spark plug cables thinking I had mislabeled them...same result.
    You need to step back and double check everything.

  6. #25
    Senior Member Old Nail's Avatar
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    What did you know about the bike when you got it? Did it run? If not, do you know. If it died at high speed, low speed, etc, or if someone just parked it in a barn for 20 years without storage prep done to it? This is the kind of info a tech needs to know,since the engine is not here in front of us, and can only guess what the problems are by what you tell us.Have you checked for spark at each plug at the correct time? Did you just replace jets without verifying all air and fuel ports are clean? Float level adjusted to factory specs? Floats operating correctly, not sticking? Float needle, spring ,and jets clean and not sticking? Give us details of what you know about the bike history and exactly what you did with it so far. Remember,this is the internet, not your local shop. One can take his bike to a shop and say"It don't run and I tried everything, and the techs will get your bike running. The bike is not in front of us to diagnose for you, and maybe a few simple things wrong that may only take a few hours to fix, but we can't help without you helping us, pictures, detailed information of the diagnostics you've done help us help you. Even the best techs in the world can't help you, without giving us the info that they need.Damn, it's sunny and about 45 degrees out. Time to do my safety checks and go for a ride! Later!

  7. #26
    Junior Member kbwill's Avatar
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    The bike ran fine before I took it apart. I'll work on getting pics and continue messing the with it. I disassembled the carbs and cleaned them when I changed jets. I have a siphon hose going into the fuel line while I work on it. Floats are working and clean.

    I'll check the sparks more thoroughly since most other causes of these symptoms have been eliminated.

  8. #27
    Member jackattack's Avatar
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    So it ran fine, you changed parts, it ran like crap, put old parts back on, still runs like crap. Something that you did is making it run bad. Check your work.

    75% of all "carb problems" are actually electrical problems
    90% of all "carb problems" are caused by inexperienced people taking them apart
    82% of all statistics are made up on the spot.

  9. #28
    Senior Member Old Nail's Avatar
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    Quote Originally Posted by kbwill View Post
    I put the stock jets and airbox back on. As for the exhaust, it's going to be unbaffled (for now) because the baffles are gone. Because I can't restrict the exhaust, I left one needle shim in; thinking this would richen it a little to compensate. Still having the same issues. I reversed the spark plug cables thinking I had mislabeled them...same result. At this point, I could care less about the pods, the airbox doesn't look that bad anyway.
    KB, get the coil/plug wiring figured out? When sitting on bike, starting from left, cylinders are 1,2,3,4. #1&4 go to the left coiland2&3 go to the right on most older Japanese Fours. However, on the 92 nighthawk, #1 goes to bottom of right side coil and #4 goes to top.#2 goes to left top coil and#3 goes to the bottom, according to Honda shop manual. Supposedly the clymer manual got it wrong. Are the coil primary wires connected to the harness correctly,that run to the ignition components? Fuel system. Plug off vacuum line if using remote tank and make sure fuel line is connected to fuel port on carb and not vacuum port. I know this is all simple stuff, but should all be checked anyway.

  10. #29
    Junior Member kbwill's Avatar
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    SOLVED: I put duct tape over the ends of the exhaust except for a small open space, and it started! There wasn't enough back-pressure to get started, and that turned out to be the source of the backfiring. Now I'm going to put the pods back on and rejet it...just kidding! I just want to ride it! It's way too loud at the riding RPMs so a new exhaust it is anyway.

    Thanks for all the help. Sorry for being a bit stubborn and maybe a bit ignorant. I learned a ton working on this thing the past few months. Thanks guys!

  11. #30
    Senior Member kerosene's Avatar
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    glad you made progress and learned on the way.

    Riding is a good objective vs. "the open look"
    -

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