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Thread: Dumping the Demon - Need ideas

  1. #1
    Kurtis500
    I'm getting rid of the 850 Demon carb. I'm looking at another Holley 850 with a choke, a TBI, or EFI. Its a rectangular port BBC with mild parts in it. I'm not going to go forced induction..... Just want something easy to start and runs fine. The demon did great in everything besides off idle acceleration. I could finesse it enough at the right engine temps and conditions, but outside of those, it stumbled everytime. I even went with the experts specially made manual of the BG Demon. I got a race boat to screw with, so I have no patience for this one. (especially when theres 4 adults and 6 kids in the boat that stumbles off idle.)

  2. #2
    mrcrsr
    i tried an 850 demon on a blown small block, and same thing!! anyway, carter(or edelbrock) carbs are basically the same, and a 750 to 850 would be good for what you have, for max power the holley would be a good way to go, i would have liked to have thrown that demon carb through barry grants window!!!!! ps - and i tried jetting and power valve changes

  3. #3
    Floored
    If I ran a 55 or 65 PV then I would get that. Try to drop it in the water on the trailer, tied down of course, and put it in gear and check the vacuum. Then slowly accelerate while watching the vacuum gauge. On my boat the vacuum rose slightly before dropping down enough to open the PV for enrichment and I got a hesitation when trying to pull skiers or just slowly accelerate. I idled at 9.5 in of vacuum and ended up using an 85 PV and it cleared up the stumble I had yet at cruise the PV is still closed for economy. All it took was about a half hour and a couple spare PV's and a vacuum gauge.

  4. #4
    Ultra Compulsive
    Really sorry to hear, my new 850 works like silk...all the way through.......gained some horses too....

  5. #5
    Kurtis500
    I'm looking for a Holley 850 to replace it probably. I cant get much info on anyone who has switched from carb's to TBI or EFI on the same engine in a boat.

  6. #6
    Unchained
    After running carbs for years and then switching to EFI I wouldn't have anything else now. Anything but EFI / engine management is "old school".
    It's a learning process though, You have to understand the system and tune it using a wide band O2 sensor or you're going to have major frustrations. There are many parameters that can be adjusted.
    I've adjusted the throttle pump settings (it's just called a throttle pump, it's really all injector timing) on my Haltech setup so I can just flatfoot the gas pedal from an 800 rpm idle and it takes off like shot from a gun.
    I can't imagine a V drive guy going that way though. Don't you want to run an Enderle ? :idea:
    If you want to call me I'll be glad to go over the setup / components.
    Mark
    616 813 7237

  7. #7
    Itsahobby
    Can you run a O2 Sensor with water in the exhaust?
    Just curious.
    Hobby
    After running carbs for years and then switching to EFI I wouldn't have anything else now. Anything but EFI / engine management is "old school".
    It's a learning process though, You have to understand the system and tune it using a wide band O2 sensor or you're going to have major frustrations. There are many parameters that can be adjusted.
    I've adjusted the throttle pump settings (it's just called a throttle pump, it's really all injector timing) on my Haltech setup so I can just flatfoot the gas pedal from an 800 rpm idle and it takes off like shot from a gun.
    I can't imagine a V drive guy going that way though. Don't you want to run an Enderle ? :idea:
    If you want to call me I'll be glad to go over the setup / components.
    Mark
    616 813 7237

  8. #8
    Unchained
    An O2 sensor would have to be in the exhaust ahead of where the water dumps in or the exhaust would have to be run dry until the fuel maps are tuned.
    The O2 sensor could be removed after the fuel maps are tuned and then it would be running open loop. I'm running open loop now but I still have the O2 sensor hooked up and it's mounted in front of the seat so I can monitor it.
    Closed loop is more desirable because it is constantly adjusting to stay at the proper mixture just like your car. The O2 sensor doesn't like leaded fuel long term so it would be best to run unleaded when setup for closed loop.
    Check out how clean the exhaust is coming out the pipes at 7000 rpm / 20# boost,
    http://www2.***boat.com/image_center...iredoutjet.jpg
    It's running 12.3:1 Air / fuel ratio at WOT

  9. #9
    SmokinLowriderSS
    I'm concerned you may have a size missmatch going on. I'm running a 454 but with large oval port heads and a 700 Holley.
    The 850 combined with the larger ports may have your port airstream velocity so low that it is causing you problems. Those Rectangular port heads work great at high-rpm's but cause trouble at lower revs because mixture velocity falls below a certain point and fuel drops out of the airstream, puddling in the manifold. I'd probably first give some effort to the power-valve tuning that was advised and then, if I was still dumping it, I'd drop down to a 750 or even less. I would also consider trying to "patch up" the port-runner hugeness with a vac-seccondary carb if you want something as big as an 800+.
    I've done some computer-dyno comparisons on my 454 (less mild than she was stock but still 8.5:1 and cammed to .565" lift) and a larger carb gains me virtually nothing (except more gas consumption). If I was peaking my RPM's out close to 6,000, maybe, but I am only topping out arround 5K.
    All the ideas I have. Best of luck.

  10. #10
    Floored
    If you have a river trip in the future let me know and I'll spend a couple hours getting it dialed for you. Carbs are easy, wives are another thing altogether. No charge, I love a challenge.

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