I have an 18 Donzi with a 330hp 454 in it. The boat has always had a very small mid range bog but I never looked into it and assumed it was carb. It did not bother me enough to look into why. Last year all of the sudden after the boat warmed up it would die at idle. I rebuilt the card and it still did the same thing, replaced points the other day still the same thing. Anyone have any ideas. It starts up good, seems to run smooth for about 15 min then it will start surge almost like a blower roll, slowly at first then more and more tell it dies. I have not done plugs since I purchased the boat because I don't put a ton of hours on it. Maybe the stuff I use to winterize fouled up a plug? I have not tested to see what it is pulling for vacume. I am going to try and get a friend to help me out this weekend if he can.

Definately start with the basics first. That way you can honestly say that they were done recently. Plugs, cap, rotor, see if the plug wires at least look good, fuel filter, and water seperator. Do you have a fuel pressure gauge on it ? Whats the pressure at idle ? Have you checked the timing lately ? Get these things checked off...then go from there sir.

Plug wires seem good, Cap, rotor, points all redone and timing done with zero change.

Replaced filters as well no change.

Would the fuel pump be the issue if it runs perfectly at WOT?

When it dies it will start right back up again with a very small amount of throttle.

Headed out to try and pull the plugs now just to see. Hope I can beat the rain!!!

Thanks

I would guess that its not the pump if it runs great at WOT. What carb are you running on it ? Lets get the plugs changed first. Next, does it have a choke on it ? If so..is it opening all the way after its warm ? Disconnect the wires from it (cover them with electrical tape), then try it again. I zip-tied my chokes wide open, and dont use them.

Got new plugs today. Hope the rain stops long enough for me to put them in and test things out. Hope it is that.

Could it be bad fuel? Still last years fuel. I have never had a 330 be picky but????

It is a quatra Jet Carb.

Look at the carburetor boosters on the primary side. At idle there should be no visable fuel dripping from the boosters or the accellerator pump squirters. If the needle and seat are bleeding fuel past when closed the engine will die rich at idle and show fuel dripping from the boosters. Try and determine if the dying at idle is caused by a fuel rich condition. Quadrajet style carbs also have plugs on the underside that are connected to the fuel bowl, normally these bleed down when the engine sits, and the engine is long crank to re-start. At idle these plugs are subject to high vacuum and could be dumping fuel also.

I put new plugs in today and it is running much better but still stalling. The old plugs looked really good nice and tan considering..... I may have a case of bad fuel at this point? I can not remember how old it is. I am going to try and get a pony tank onto it and see how it goes tomorrow if the rain holds off....

Vacuum leak?

Your problem sounds like the same issues I'm having. I've gone through the plugs, wire, cap, rotor, carb, vent line, inline anti-siphon valve, fuel fitler....... When your engine is stalling or stalled give your carb some gas and see if its squriting fuel. If not its a fuel issue. Mine is a fuel issue but I can't track it down. Last night I put a new fuel line from the tank to the water seperator. If that doesn't solve the proplem then my boat is getting new fuel pumps as that is the only thing that hasn't been rebuilt or replaced in the fuel system.

Ok today I pulled off the fuel line and hooked it up to a pony tank to make sure it was not bad fuel. Still ran the same, no change at all. I am down to a vacume leak under the intake manifold or something wrong in my carb?