I honestly dont think your probem is in the carb. I could be wrong, but to me it sounds like an igntion probem. First thing you have to do is get a timing light on it. Check timing, firing order is clockwise on the cap-18436572. Cylinders are as follows, right bank(standing in front of engine) 1,3,5,7 Left 2,4,6,8. The ignition system is fairly simple. The module could be bad, but I doubt it. There's also a sensor in the distributor that I had to replace last month on a friends 454. It caused a no start condition.

Hard starting, missing, popping, sounds like ignition. But, because its a fresh motor, theres also the possibilty of The new cam going flat. Break in is very important, and all that idling will kill a new cam if it wasnt broke in right. Also happened to me before on a 454 mag. Wouldnt hurt to pull the oil filter and look for lots of metal shavings in the oil. Chances are though with all the smoke out the exhaust, the valves are probably opening letting fuel in and out, but its just not igniting. You have plenty of carb, considering guys run 502's and 540's on an 850 carb. Personlally, at this point, I wouldnt waste time playing with jets and stuff, get it running first, and make those adjustments later. Also, when you get it running right, change the oil immedialty. Its probably got a bunch of fuel in it, which will kill your new motor. Good luck. MT

By the way, if the popping is constant when you revit up, like pop, pop, pop, pop, I'd say a flat lobe on the cam. Does it pop thru the exhaust or intake? Who adjusted the rockers? Set base timing to 10 to start. Have someone crank it and put your ear near the carb and listen for air poofs thru the carb. If a exhaust lobe is flat, you will hear air come up thru the intake because it has no where to go except back up thru the carb.

clean all your air bleeds on the carbs they get drity quik

Well..... timing was fine, advance working fine (up to 35 degrees) compression fine, everything fine.......

Frustrated I switched carbs guess what...problem gone! No adjustments were made or anything. I thought it was wierd but when I was bolting the port engine carb on the starboard I noticed that the right rear bolt was bottomed out but not seating the gaskets together and there was a space on the intake manifold allowing an air leak under the carb. I pulled the bolt out and added 2 more flat washers to make the bolt head higher up and allow it to tighten fully adainst the intake. If that was the same case when it was on the port engine I could see how that would cause a bad air leak and stumble the carb. I ran it from Old Saybrook CT to Mystic, CT and it ran great the entire way. Still some things to mess with of course but I'll post a new question for that if I need to.

Thanks to everyone that helped with this especially MildThunder.....your idea of swoping carbs worked.....I just wish I had read your response before I went to work on it today....I would have started there......

New thread for the tweaking process soon.

Glad to be of help! Good to hear you got it fixed and running better. Now, send me some pics of the 390 stinger. Its basically the same boat as my excalibur Hawk.

Well.....took her out today and the same problem occured now on the right engine. Whatever the problem is it seems to have followed my carb swop from left to right. Ran good on the way over with little idle time. After the run....20 min of idle in a no wake. Started it today, and idled 20 min out into the sound. Gave her power and right engine only got to 2000 RPM. I throttled down and it ran terribly all the way in.

I am still thinking rich running fouling plugs out and not getting me any power. Does a vacuum leak cause an engine to run richer or leaner? How do I get this carb to lean down? 4 corner idle screws only 1/2 turn out on the primarys. Have tried different settings with no effect. How many places can I get a vacuum leak?

I'm going to change the plugs again tomorrow (BR6FS NGK) Clean out the carb again, check the jets on the other carb and match them up....any other ideas, this is getting old on great days like today. I can't seem to get my wife a ride on plane which is not convincing her that this is the best place for our funds.

Todd

have a good carb guy go thru it. i had a problem with 1 of my dominators three shops looked at it until a guy that really understood how all the carb cuicuts intreract saw my problem as soon as he looked the carb over. cost 60 bucks for him to go thru it. my boat rons and idels sweet now.

I have 1" spacers between the carbs and the power plus hurricane high rise single plane intakes installed. Is there any need for the spacers? Are they really doing anything especially with an intake that has a high rise to it? Is this just another place for a vacuum leak?

Thanks

It does not sound like a vacuum leak. A vac leak will make the engine lean. It will only idle at high rpms and will stall when put in gear.

Take off the flame arrestors and look down into the carbs. Look for fuel dripping. If it is dripping then you have a problem with the needle seats sticking and or the floats. If not chances are that a powervalve is blown. Also, you need to set the float levels with the boat in the water or at least on a hill so it is the at the same attitude as it would be sitting in the water at idle.

Also 850's are more carb than you need, but they should still work ok.

Is the power valve on the Demon the same as a Holley generally? I replaced the needle and seat last week, and set the float level mid way up the sight glass with the boat in the water. I did not notice fuel dripping into the carb but I'll look again. Would a even slight backfire cause the power valve to blow out?

I have been thinking the 850 is too big. I have had some people telling me it is too small which I could not believe. I was thinking a 750 or 800 would be more appropriate and fuel efficient than an 850. The engines came with these carbs though and I am reluctant to spend $800 - $1000 on new carbs right now.

I'll replace the power valve today and see what happens.

Thank you,
Todd