Dumping the Demon - Need ideas

[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.)

[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

[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.

[Ultra Compulsive]

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

[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.

[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 ? :D :idea: :D
If you want to call me I'll be glad to go over the setup / components.
Mark
616 813 7237

[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 ? :D :idea: :D
If you want to call me I'll be glad to go over the setup / components.
Mark
616 813 7237

[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/data/520/220airedoutjet.jpg
It's running 12.3:1 Air / fuel ratio at WOT

[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. :cool:

[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.

[Kurtis500]

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.
Floored you are very kind.
I have decided that a new Holley 3310 780 vacuum secondary will be the first test. I believe the 850 Demon was too much all along, but it came on the boat when I bought it. With about 40 hours on the motor I have spent maybe 30 seconds at full throttle. I like to cruise and go slow, along with being safe and having fun with friends (kids too) in our boat. My next project is to quiet the noise down. I have an injected hydro and a blown injected hydro for all my speed needs and desire to screw with things. I want my cruiser to be like my vehicles, reliable and quite. One day a good programmable EFI system will make its way there.

[cdog]

I've got the holley 950 commander system and so far it's done really well. I have the wide band O2 up grade with it. Those systems are bank fire EFI which is all you need for N/A. Give me your email and I'll send you some pics of it.

[Floored]

Thats what I run,3310-3, and it works well for everything I do.

[mrcrsr]

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. :cool: what is your engine combo?? i just got done putting together a pair of 454's for sterndrive, w/ stainless marine exhaust, mild(268/272 dur, 540 lift)comp cams, large oval port heads, edelbrock performer intakes, brc roller rockers and am currently running q-jets but am getting ready to switch to holley 750's, is your combo similar, and what is your power output?

[Maxey]

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.)
I think (from my experience) that that carburetor is too large for your engine to get the crisp off idle response. does it have "down leg" boosters? or "annular boosters". If down leg, send it to demon to have it converted to annular boosters. They will create a better low speed vacuum signal and will help your situation. A 750 demon might be better. Demon carbs are "head and shoulders" above Holley IMHO.
Dave :)

[SmokinLowriderSS]

what is your engine combo?? i just got done putting together a pair of 454's for sterndrive, w/ stainless marine exhaust, mild(268/272 dur, 540 lift)comp cams, large oval port heads, edelbrock performer intakes, brc roller rockers and am currently running q-jets but am getting ready to switch to holley 750's, is your combo similar, and what is your power output?
454, 2-bolt clean bores, cast crank & pistons (8.5 to 1), stock rods
Large port oval heads, 122cc open-chambers, 2.06/1.76 (the small big-block valves)
Isky cam & superlifters and matching springs (flat tappets) .565" lift, 280* duration, 1.7:1 rockers 3/8" pishrods & guides installed straight (custom ground 4* adv).
Edelbrock Performer RPM Air Gap 2.0 manifold
700 CFM 4150 style Holley mech seccondary carb, jetted pri 66 / sec 76 w 6.5 PV in Pri only.
K&N Filtercharger 14" element air cleaner
Niccson log exhausts (soon to become Lightning headers & 4" outlets thru-hull)
Acording to all I can see in Desktop Dyno, JP Calc, crossed with the tach on my boat (& test tools), Berk A $ 4800 RPM in a fairly tight drive with a good loader:
355 to 350 HP @ 5000 to 5500 (nice & flat) Torque, 400 to 412 to 398 from 3000 to 4500 RPM, still holding 373 @ 5,000.
Next year looks even better with headers (418 @ 5000, 421 @ 5500 torque, 461 @ 3500, 465 @ 4000, 460 @ 4500) and the following year a porting should reach me to arround 470 HP @ 5500, torque 472/482/485/475 @ 3500 to 5000.
That should run me an A at 5300 RPM, right in the heart of her power.

[GUGS102]

Kurtis -
I just built a 489 solid roller motor and the 750 I have is too small. I have a marine edelbrock 750 and a holley vac secondary holley. You could try both.
Since you are in Phx, maybe we could get together and try a few different arrangements.
I am looking for an 850 holley or BG
Shoot me a call, this could be interesting, lots of options, we'll take the gps and see what both boats like.
Tony
623-376-0366