Black Smoke
 

I have twin 454 Mag Bravo's. I installed Whipple Superchargers and Holley 750 carbs. Other than that the motors are stock. The carbs were setup for the blowers by Teague. I have a 12 minute no wake ride down the river to Lake Michigan. The whole time the engines were dumping out black smoke and the smell of gas very strong. The motors didn't run well at all. I could hardly reach 4800 RPM with 25p Mirague props. The next day both motors wouldn't start. The NGK-R5673-8 plugs were jet black. I had a marine mechanic adjust the carbs and change the plugs. He used Champion V 63 C plugs. I took it out and the same thing happened. Black smoke and fouled plugs after one ride. The motors ran good at first but the next time I started the motors they ran rough and wanted to die. Teague recommended that I turn the idle mixture screw one turn open from closed and check to see if gas is dripping in the carbs when at idle. :confused: Any help would be appreciated.

Do what they said about checking to see if you have fuel dripping at idle. If there is some, chances are the floats are set too high. I would alos remove remove the sight plugs on the sides of the carbs to check the float level. Fuel should be right at the bottom edge of the sight hole. Do this with the boat IN the water to get an accurate setting.

As Griff stated make sure your float levels are not set to high. Also what fuel pressure are you running at idle? If it is to much it will overfill bowls regardless of float settings.

What 750 Holley are you running? Is it a mechanical secondary? I have the same setup on my boat but I am running a Barry Grant Race Demon 825 carb. I had a similar problem and you need to make sure that both butterflies are set at the same opening at idle. I also leaned out the rear idle circuit because it is closer to the Idle Air Bypass that is on the Whipple. This stopped it from loading up at idle.

Also what power valve and jet sizes are you running? Let me know so I can help get you the rpm you are missing. My motor spins a 26" Bravo 1 to 5000 rpm anytime.

Dave

The floats were not adjusted with the boat in the water, so I'll recheck that. I haven't checked the fuel pressure yet. I'm using the stock fuel pump. I think its rated at 7psi. The carb is a 04779-C. On the body it has stamped 47779-90752. I couldn't find this number on Holleys site. They are mechanical secondaries without chokes. Teague did not tell me the size of the power valves or jets. I will find out.

Thanks, Roger

Dave,

The power valves are 10.5, primary jets are 85 and the secondary jets are 90.
I'm trying out Hydromotive 28p Quad IV's. Before the second set of plugs fouled, I had great acceleration and from the throttle room I had left, I think it could reach 5000 RPM. Lake Michigan was too rough to risk WOT that day. The next day out, the starboard side motor would stop pulling at a little over half throttle and every time I tried to trim the drives the RPM's on that motor would go low. I'll make the adjustments that you guys recommend.
New plugs are on the way. I should be able to try again Sunday.

Roger

My guess is those jets are close. Either float level 2 high or you have blowen the power valves.

Quiet Storm...

Although you didn't mention it this would seem to be the first time you fired the engines after changes... Everyone has the right idea and I would be willing to bet that the power valves are blown... It only takes one small missfire and you are there...
Since you mentioned that the application is stock and the cam
was not changed you should have a smooth running non-black smoke application, although do not discount checking the float levels... Just eliminate the fuel dripping down the throat of the
carbs...

Tnx, Karl

PS... Not sure which Holley you have but it could have two metering plates and power valves...

Karl,

You are right. This is a new installation. I did have a problem with leaking intake manifold gaskets and the timing. It did backfire and blew through the carbs. A mechanic set the timing and I replaced the intake gaskets. The first time I took it out it ran OK, but then fouled the plugs. I figured that the carbs needed to be adjusted by a professional and the plugs replaced. I took it back to the same marine mechanic and he replaced the plugs and set the float levels. He said it was running great in his shop and it ran great in the water. Untill the plugs fouled again. It sounds like the power valves are blown but don't you think the mechanic would have caught that? He was aware of all that happened. Is there anyway to check the power valves without removing them?

Thanks Roger

I am not an expert but
 

what kind of ignition you are using? is it stock?

I'm using the stock Thunderbolt IV. I saw that somebody was having a similar problem and went to MSD ignition and was able to use the stock distributor. It didn't sound all that hard to install, just be carefull with the wiring. I've been suspicious of the ignition for a long time. Even before I installed the Whipples the motors had a tendency to foul plugs. I had the carbs rebuilt but that didn't seem to help.
I talked to a tech. from Holley and he said to check the power valves without disassembling the carbs, I should close the idle mixture screws. If the motors die the power valves are good. If they keep on running thats where their getting the gas and they are bad.

Roger,

Unfortunately most of the marine mechanics are not at all familiar with "high performance" applications and at the end of the day end up guessing, with your money, what the problem might be...
About the only way to check the power valves is the look down the throat of the carb trick... At an idle the fuel should be vaporized for the most part or maybe just an occasional drop which you can see... If they are bad you will see nearly a stream... Are there metering blocks/plates on both ends of the carb... If they are bad about the only places I could find the parts were the local speed shop... They are sized by the amount of vacuum required to keep the valve closed and that number is stamped on the valve... Once you cure the mass fuel problem the mixture screws on the carb can be adjusted...

Tnx, Karl

PS... Once the problem is resolved I would also suggest changing the plugs again...

If its a newer 4779 then it should have Power Valve blowout protection. 4779's only have a primary power valve I believe.

PS, there was a boat called Quite Storm in South Haven Michigan last weekend. Was that you?

Karl,

Thanks for all the info. I'll check it out this weekend. There is a speed shop close to where I go in Michigan.

Chris,

I heard that the carbs. may be protected. They should be new, I just bought them from Teague. When I asked them the size of the power valve, he only gave one size. I'll check with them.
If the Quiet Storm was a 28' red Checkmate Convincor, that was me. Did you come to South Haven for the poker run? Did you have a boat there?

Roger

I changed the power valves. Changed the spark plugs. In the water gas was dpipping into the carbs. Readjusted the float levels. Everything looked good. Ran fine, no black smoke, no dripping gas into the carbs. Took it out and it ran great. Lake Michigan was too rough again to run WOT again. Coming back in it started to run rough. Revved it to clear thing out. Everything started to work fine again, then the starboard motor started to back fire. Shut it off, put it on the trailer and took it over to Bruce Wolff's. Somebody on here recommended this guy. I hope you are right about him. I'm sick of this *#^&.

Storm,
You are in good hands at Wolffies. He rebuilt my 454 this year and I am very pleased. Still have some dialing in to do. No big deal. Was there last Friday and had the pleasure of listening to SYNERGY's (Cigarette out of Chicago)new motors. AWESOME!! He will take care of you.

Paul

Could your problem be that the gas is peculating? If things ran fine until it heated, up, it is possible that the gas started to boil in the carbs. Just a thought.

I lost track of the thread. Yes we were in the water at South Haven to watch the poker run. Maroon and Whit Liberator named Miss Demeanor. We are in SH alot as the inlaws live there. Give me a shout if you ever want to hook up.

If you ever need Holley parts for tuning I have a complete selection of jets, springs, and a good number of power valves as well as vacume guage etc.

I had put up a post about Wolfeies. Others have had great things to say as well. Good luck.

Fever,

I don't think the gas overheated. I have not seen allot of heat in the motors. At idle the temp gauges read 110. But everything started to happen fast and I just shut it down. I'm not sure what happened. Unless something is very wrong, Wolffie said that he would have it right by the weekend.

Chris,

I'm sure that I saw your boat. I've had allot of time to sit on the deck lately. I plan to be in South Haven over the 4th. Stop by, I'll find a place for you to dock for awhile.

Roger

Finialy got it . Wolffies is the place to go. He found about a gallon of gas in each block, fouled plugs and a lousy set-up. He put in MR43T plugs. Changed the power valves to 6.5. Rejeted the primarys to 76 secondarys were left at 90. Set the timing to A+ 31. Reset the floats. Changed the oil & filters. This is the short version. Wolffy put alot of effort into dialing in the motors. It starts and runs great. No problem with long idling or cruising. I will still have to play with props but the main issues with the motors are resolved. Thanks you all for the advise.

Roger

Tell us about your top speed:D :D Nice boat!! I was checking it out when I was by the shop a couple of weeks ago. We dialed mine in this weekend as well. Have fun!

Paul

The power valve protection devices seem to be hit and miss I have 3 carbs with them and power valves still blow. For the price of a real good carb these days throttle body injection seems like a option which comes closest to producing power of a good carb setup.

Paul,

I was a little disipointed with the top speed. It reached 78 at 5000 RPM with a full tank. It ran out of HP turning the 28p Q-IV's and they gave me too much stern lift. The props turn in. I want to try some 27 or 29 Mirage but for this year I ran out of boating money. Maybe I will find some to try out or trade for the Hydromotives.

Roger