330hp 454 dies at idle.
 

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. :drink:

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. :drink:

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?

Sounds like the coil is bad once it gets warmed up.

Richard, if the coil was bad wouldn't it get worse at higher RPM's. or show up as a skip at all RPM's?

When rebuilding the carb, was the carb soaked in order to clean all passages? also were the idle mixture screws adjusted?

No it was not soaked we just sprayed cleaner and then used compressed air to clean them out. Idle Mixture screwes I have messed with. When you get it running OK warm then it is a mess cold and vice versa. I am really starting to lean towards the carb needing to be rebuilt again.

Jon

Get rid of that quadra-junk, and put a holley on there. Simple swap...and easier to work on sir. :drink:

330's have run for ever on the Q jets. They are nice and efficient as well. Wouldn't I have a lot more fuel burn with a Holley and also have to swap over the intake?

No on both counts. :drink:

What intake are you running ? It more than likely has the stud holes in it for both style carbs, and if not...they make an adapter.

Here are a couple examples sir. See the extra holes ?

Have you watched the carb as it goes thru this cycle? Does the choke flutter and then close making the engine die?

I had this same situation on a truck I used to have with a marine q jet... Zip tied the choke open and no problems...

I asked him about the choke earlier....but he never answered back about it. ?????

Choke is open all the way sorry about that guys :D

Surgeing
 

Many times this is caused by not adjusting the carb correctly.
Get something to check the true RPM like a dwell meter don't use your tach. (too much fluctuation)
Start engine get warm and set your RPM to desired speed 800-900 maybe.
Then hook up a vac gage and then adjust your curb idle screws in or out at a 1/4 turn at a time until you get the highest reading on the vac gage. DO-NOT rush this.. 1/4 turns only and then let motor run out a little. Then make another adjustment. After each adjustment re set RPM,, YOu may have to go around 3-4 times..

I have done this for many a friends,, They tend to rush this or set by ear.. Do it right and take your time..
My BG carbs had 4 screws and on twins this took me about 2 hrs,,but purs like a kitty..

Update:

Looks like my problem was a bad carb. We had rebuilt the one that was on there but it still ran the same. I finally just grabbed a carb off my other boat with 330's and rebuilt that one. It is now running better then ever. There may be some vacume leak in the old carb some place that we are not seeing? At any rate for me it was the carb. Thanks for all the help guys!