carb 308 backfire power loss? | FerrariChat

carb 308 backfire power loss?

Discussion in 'Technical Q&A' started by carb308vt, Jul 6, 2008.

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  1. carb308vt

    carb308vt Karting

    Apr 12, 2005
    122
    NYC/Vermont
    Full Name:
    Craig M
    Got stranded today. Went to start car up this morning at GF's house and didn't hear the fuel pump running. I checked the pump kill circuit under the seat to make sure it han't been diconnected-(let my girlfirend's oversized son in the driver's seat the previous night)-probably could have diconeted it-nope-looked good. Popped the fuse box and wiggled the fuse-and got it to work-great! Down the road by the golf course 'BANG' loudest backfire I've ever heard-like a sonic boom. Engine starts losing power or misfiring I guess. Have to pull over to the side of the road. Start up again and more "BANG'BANG"- people in the neighborhood probably thought they were under attack. Luckily made it to my sister's house where it is now. What could it be? Backfires are caused by unexploded fuel going into the exhaust- but my fuel pump wasn't working correctly-so are the two incidents realeted? Are faulty spark plus to blame. any thoughts greatly appreciated.
     
  2. pad

    pad Formula 3

    Sep 30, 2004
    1,426
    Tequesta, FL
    Full Name:
    Paul Delatush
    First thing would be check your ground wires. Most times, backfiring is caused by ignition issues. If you were backfiring out of the carbs, then a lean condition would be indicated pointing to a possible fuel pump problem. (Let's hope your valve timing has not shifted, or an exhaust valve has not failed).
     
  3. Red 27

    Red 27 Formula 3

    Feb 2, 2008
    1,002
    San Diego, Ca
    Full Name:
    Dave
    Craig,
    Might still have a loose connection in the fuse box and when it contacts it is igniting all the unburned fuel.
    Backfiring can also be caused by a sudden drop in fuel pressure from a faulty fuel pump or plugged fuel filter.
    Dave
     
  4. carb308vt

    carb308vt Karting

    Apr 12, 2005
    122
    NYC/Vermont
    Full Name:
    Craig M
    Thanks Dave, yes it seemed a bit of an odd coincidence that I had to wiggle the fuse to get the fuel pump going. A couple of years ago had the same problem but i don't remember backfires. I just assumed unburned gas was going through a cylinder due to a bad plug and then exploding in the hot exhaust, but the loss of power was a clue that the fuel was not flowing. If low fuel pressure can cause a backfire then that must explain it?
     
  5. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,367
    NY
    I guess I never heard that a faulty fuel pump would cause a backfire. Usually it is caused by an ignition problem where a sparkplug does not fire and raw gas goes out the exhaust valve and ignites in the muffler causing a large backfire. If you get more then 1 plug say like a bank of cylinders it sounds like a cannon firing. If you are still running points the problem could be with a bad set of points on one of the banks. I had this problem when I first got my car but after almost blowing the muffler off I quickly put in an electronic ignition. Playing with the fuel pump fuse just made it work otherwise you would not have any fuel in the carbs and you could not start/run the car. So if the pump is pumping then I would look at ignition as the source of the problem.
     
  6. carb308vt

    carb308vt Karting

    Apr 12, 2005
    122
    NYC/Vermont
    Full Name:
    Craig M
    that's exactly what it sounded like, a cannon. People were running for cover! What would cause an entire bank to go down- distributor?
     
  7. Red 27

    Red 27 Formula 3

    Feb 2, 2008
    1,002
    San Diego, Ca
    Full Name:
    Dave
    craig,
    I was just looking on another forum and a guy with a boxer had the same problem. Bad fuse connection. He cleaned and replaced the fuse to fuel pump and problem solved. He ended up swapping out the panel to prevent further fuse related problems.
    Good luck,
    Dave
     
  8. FasterIsBetter

    FasterIsBetter F1 Veteran

    Jul 22, 2004
    5,855
    NoNJ/Jupiter FL
    Full Name:
    Steve W.
    If you are having any problems whatsoever with fuses, do yourself a favor and get the Birdman fuse block upgrade. It was one of the first things I did when I got my carbed 308 and it was money well spent. In fact, just do it, no matter what. It's an upgrade your car will thank you for.
     
  9. carb308vt

    carb308vt Karting

    Apr 12, 2005
    122
    NYC/Vermont
    Full Name:
    Craig M
    It's the fuse box-specifically the connection for the pump(#3). Dave you were right. Steve-I'll take your advice and get the fuse blocks from birdman. I guess I resisted because the setup looked confusing and not labeled ( i had been down this road years before and simply got used to replacing fuses on my own). It's time to upgrade.

    I drove the car today-no problems and after about 20mins- I heard a click coming from the dash-where fuses are- followed by 'G' light coming on then...... 'KABOOM", while the car was still hurtling sluggishly forward, I popped the panel, found the fuse connector and simply squeezed it together as hard as I could. Pump started up again, car ran perfectly after that. Thanks to everyone, such a great resource!
     
  10. FasterIsBetter

    FasterIsBetter F1 Veteran

    Jul 22, 2004
    5,855
    NoNJ/Jupiter FL
    Full Name:
    Steve W.
    Craig,

    The install is as easy as can be -- you simply number the connectors, left to right, top and bottom, on each block. I did one block at a time. Remove the connectors from the old block, put the new block in place, push on the connectors, in order, on the new block, insert new fuses and you're done. Even if you are mechanically challenged, the whole job should not take more than 1/2 hour, including stopping for a beer between blocks.

    Steve

    p.s. If I remember later, I'll post a picture of my installation.
     
  11. Red 27

    Red 27 Formula 3

    Feb 2, 2008
    1,002
    San Diego, Ca
    Full Name:
    Dave
    Craig,
    Glad you got her going.
    Dave
     

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