Backfire, capow!

Discussion in 'Technical' started by justin has a 74, Aug 30, 2010.

  1. justin has a 74

    justin has a 74 Maverick bandit official

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    The spout things near the top of the carb. On the secondary barrels. Must have blown something inside the carb when i drove it home that day.
     
  2. mashori

    mashori Member

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    My carb did that a few days ago and I took it to Bryant's shop. Ended up being that the needle had gotten stuck so the bowl was getting flooded. I asked the question on the board and that's what everyone was predicting too.
     
  3. maverick75

    maverick75 Gotta Love Mavs!

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    Lol remember what i said in the PM? If its coming out of there "fuel vent" its flooding. Set the needles right. Take off the fuel bowl turn it upside down and adjust it till its level. That should be your starting point.
     
  4. Mavman72

    Mavman72 Gone backwards but lookin' forward

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    Yup...Float setting is incorrect or needl/seat is bad or has crud holding it open. You may want to install a new gas filter while youre at it...:yup:
     
  5. justin has a 74

    justin has a 74 Maverick bandit official

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    And thats why its backfiring........
     
  6. justin has a 74

    justin has a 74 Maverick bandit official

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    well i threw on maverick maniacs holley that was brand new and set to the lowest float level and again, capow....


    Actually shot flames this time. Decided to take a gander at the timing chain and its spot on, which makes me think i screwed up the intake gasket some how (dont know how, ive done it a bunch of times)


    left to check is

    intake gasket
    wiring
    heads


    This is driving me crazy and costing me a bazillion dollars!
     
  7. justin has a 74

    justin has a 74 Maverick bandit official

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    btw did i mention the vacumm guage said late timing?
     
  8. Mavman72

    Mavman72 Gone backwards but lookin' forward

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    If the floats are set too low...You will starve the engine of fuel causing a lean backfire. Set the floats properly...Primary float setting should allow fuel to just barely seep out of the sight plug hole...secondaries: fuel should just be below the sight plug hole,not seeping out. Be certain to make this adjustment on LEVEL ground/pavement.
     
  9. justin has a 74

    justin has a 74 Maverick bandit official

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    You know, i have done this for 2 years, this has never happened to me....:16suspect

    Why would the vacumm guage say late timing?
     
  10. Mavman72

    Mavman72 Gone backwards but lookin' forward

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    What exactly is the vacuum guage doing???
     
  11. justin has a 74

    justin has a 74 Maverick bandit official

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    Wait, your telling me that fuel shooting out of the front horn and smoke comming out of the carb, shooting flames is a lean pop? Boy, what a dinky name for such a bu bu pain in the but.
     
  12. justin has a 74

    justin has a 74 Maverick bandit official

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    Pulsing between 13 and 16 (late timing mark.)

    I go to rev it and the needle goes down to zero and then into the normal range (17-20), then back down to pulsing:bs:
     
  13. justin has a 74

    justin has a 74 Maverick bandit official

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    people with this cam are claiming 12" vacuum at 750 rpm, 20" at 2000 rpm

    So..... lean pop?
     
  14. Mavman72

    Mavman72 Gone backwards but lookin' forward

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    With your current cam your reading is pretty normal. Vacuum drops off when you open the throttle...You are eliminating the restiction that creates the vacuum signal when you open the throttle. When you let off the throttle... the vacuum suddenly increases in response to re-introduction of the restriction (closing the throttle blades) then settles back to the normal level the engine sees at idle. I dont think you have a late timing issue...I think you have a fuel delivery problem, set the floats as I said before and go from there. Too low a float setting means the carb needs a stronger vacuum signal to begin to pull fuel through the cruise circuit. Your cam does not allow a very strong signal...Low float setting and low vacuum signal will cause a lean condition which will cause the engine to backfire. Seems you have had a few rather violent epesodes of backfireing, its possible your engine sucked in an intake gasket with the back fire. Try setting the carb up properly first and see what happens. Did you knock down the huge plug gap you were running??? If not...Re-set gaps to .035...The large gap will cause you to see a late timeing issue with the vacuum guage...Gotta remember...Instruments can give you accurate readings...You need to interpret those readings accurately to diagnose a problem...It take lots of practice and plenty of learning to get it down man...Youll get there...Try out what i gave you here and see how it goes...Good luck!!!
     
  15. justin has a 74

    justin has a 74 Maverick bandit official

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    THanks for the info, ill get right on it as soon as i get another timing chain cover gasket lol

    My carb was set at 2 1/2 turns out on each screw and ran fine with 34 gap. Now i have the 40 gap, guess im regapping again..... Cant wait till im burning the tires off..... so sick of this crap....
     

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