need help with 8896 dominator carb idling too rich. ????
 

i have a 9.7-1 comp 572 bbc in an inboard outboard boat , roller cam, 114 lobe centers, dart 345 heads. Motor was dynoed and built by ohio crankshaft for my boat application. Problem is, it runs good wide open but if you idle a little it starts blackening the plugs really bad. The thru hull exhaust is below the water line while idling also. I have tried drilling out the idle bleeds 2 -3 times larger , but still too rich. I have lightning 2 1/8 inch id water jacketed exhaust with 5 inch collectors. I assume ohio crankshaft didnt do anything for the idle while dynoing.
How can i lean and clean up the idle on this motor? It also seems to be a little rich wh ile cruising at around 3000 rpm too. Vacuum is around 5 inches warmed up idling in gear and i have a 45 power valve in front and back. 88 jets square. What to do??????????????

i would say go with a power valve block off rear and up jets to 96 drop front pv to 2.5 because i always thought take your vacuum in gear at 2000 rpm and cut it in half and add half a point , i would also check to see if you have fuel leaking inside carb while idleing . if so it could be a stuck needle and seat or float level too high . good luck

carb
 

hi i never tuned a carb on a boat but i will try to help. at 5 inch vac the power valves should be 2.5 ,3 max i would try that first . how far out are your idle mixture screw . how far open are your throttle plates with the carb off under the carb you should only see a small portion of the transfer slot below the plate you might hafe to drill your air bleeds more good luck let me know how it goes

8896 dominators do not have power valves..at least the 2 I had did not.
I dont think any dominator had them..k
sounds like it is rich in the intermediate circuit. There were a couple of books out sometime ago available at speed shops on holleys, goes into some detail on getting better idles out of those things. Some restrictor wires in the metering plate idle circuits would help. I think that applies to dominators too along with the regular carbs, its been so long, memory fades yoiu know. :shock:

Everything you have done with the carb you have is about right. Remember Doms. are made to be ran at WOT! Sounds like you need a smaller carb. I would try a smaller HP series carb, and see what it does for your application. Or try FI on this motor

Yes the dyno was done to find Max HP and torque for your motor. Not to make it idel without fouling the plugs. It's very hard to find a happy medium with a Dom at idel without fouling your plugs. What did this motor do on the dyno?

Even a perfectly tuned dominator on a drag car will turn the plugs black when you idle around,you have to make a pass or two down the track to clean them back up.I would try a 4150 style carb if the boat is just used for cruising.But like stated before you need to make sure that the fuel is not going through the needle and seats.If it is there will be fuel possibly getting in your oil.

if the boat was used for cruising, i wouldnt have a 572 bbc in it. It runs over a 100 mph when topped out and cruises also looking for a race. It is a real sleeper. dont want to put a smaller carb on it and kill the top end. There is bound to be a way to stop the plug fouling.

Get rid of the 8896,Them were never a out of the box carb,Them carbs are not for the inexperianced type carb tuners

I'd suggest selling it or send it to Patrick James @ pro systems, take your losses,and buy a 9375 annular discharge dominator

Personally I buy a "flowed one from pro-systems,give Patrick a call bet he'd get you set right up out of the box

http://www.pro-system.com/

rich idle
 

I have twin 572's in my 32 fountain, starboard motor has same problem as yours-running to rich and fouling plugs. Port motor runs like a dream. Both engines obviously are identical. Took the starboard 8896 apart 3 times and couldn'tfind anything wrong with it. 91 jets on all four corners and 3.5 power valves front and back - exactly as the port motor. Even had a few bracket racing buddies look at it and still couldn't find anything wrong. Frustration pushed me to a new 8896 which should be here by weeks end, hope it works!