Quiet Storm

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. Any help would be appreciated.

Griff

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.

Smitty

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

Quiet Storm

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

Quiet Storm

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

Turbojack

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

Thunder1

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...

Quiet Storm

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

timucin

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

Quiet Storm

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.