Turbojack

Did rpm go up when swaping pulleys? You say 3.5 pulley, what is the size of your crank & blower pulley?

When I have a loose belt everone in boat with me is telling me belt is loose because they can hear it.

I snaped to your name, Boat ia fountain Feaver?

GotTheFever

I checked the rev limiter and ignition system including the timing. I’m at 32 degrees full advance. The 4700 rpm is the rpm where if I open up the throttle any further, I start seeing boost on the boost gauge. If I slam the throttles before this, I don’t event get to 4700 rpm. If I ease into the throttles, when I reach 4700 rmp, the boost quickly climbs up to 3 lbs, but my rpm starts to drop off by a 200-300 rpm.

The 502 is stock except for the items I listed in the earlier post. The Procharger is a M1. I think that I confused you with the 502 carb (X2). I meant 2 engines, not 2 carburetors. Both engines are experiencing the same exact problem

About your other questions: The boat is a 1993 32’ Fountain Fever. The prop is a Bravo-1 28” 4 blade. Drive gears are 1.5 to 1. Compression is stock, timing is 32 degrees full advance, exhaust is CMI 2 piece, and I always use 92 octane gas. The ignition is stock except an Accell Supercoil. Plug gaps are .035. The engine compartment is closed, but I have an automatic hatch opener that I sometimes use while underway to get fresh air into it. It does not make any difference. When I swapped the pulleys, I also had the carb worked on. I don’t know the diameters of the pulleys, but ProCharger ensures me that they should produce the 5 lbs of boost.

Thanks again for all the help.

Turbojack

Try backing your timming off to a max of 30. The problem has to be 1- fuel, 2- ignition (boost is keeping plugs from firing) 3- Detonation (what is your water temp gauges saying) 4- belt slipping (I don't think so) Interesting thing is both motors have exact same problem.

Have you put a bigger prop on since you procharged?

GotTheFever

I can try adjusting the timing. I’m concentrating on it being a fuel problem, but don’t want to rule out ignition. I was under the impression that the Mercruiser ignition with a 50,000 volt super coil should be sufficient for an engine with 5 lbs of boost. I was thinking about upgrading to a MSD system, but with twin engines, you always have to buy 2 of everything, and they are not cheap. When I installed the Procharger, the instructions have you take out the thermostat. The temperature gauge never reads over 100 degrees. The oil temp stays around 200 – 210. I did go from a 27” Spenelli to a 28” Bravo I. The Bravo has a larger diameter. If I can ever get these engines running right, I might have to go to a 30”, or at least that is my hope.

Dixie Doug

run it without the flame arrestors,see what happens.

Turbojack

Grasping for straws. Cheap things to try.

First try to back timing to 30. If no change replace sparkplugs with new regaped plugs at 25. These changed will not make HP but maybe see where weak link is.

Look & mark throttle where the motor starts falling on face. Then after marked look at where throttle shafts are at that setting. I am wondering how much in secondarys you are into. If the secondarys are too rich it could cause the motor to start falliing. You say you think fuel but it sounds like the amount of fuel you have check out.

Another though is your valve springs are worn out. Once motor starts going in boost the valve springs are not strong enought to close at the high rpms. How may hrs are on the motors?

I would say your prop is too small. I feel that your motor should be in boost before 4700

GotTheFever

Turbojack,
Thanks for all the input. I’ll try your suggestions. Unfortunately, the next time I’ll be at the lake won’t be until Labor Day weekend. I’ll let you know how it goes.

bsc

I hope I am wrong.
last boat had, 350 mag with a weiand supercharger 142. This thing was a rocket up to 55mph and then would loose power and die down to 30 mph plus making nose at those speeds, at idle, sounded perfect. spent tons of money fuel to electric. The bad word was detonation. Check your compression.

Turbojack

bsc - that is kind of what I was also looking at. that is reason to try less timing, & my asking about engine water temp.

bsc

On the 350 mag at 5 lbs of boost, safe to run 28 to 32 on timing,, Found this out after I blew the motor. @ 32 on timing, high octane and low air temp.
Good luck on the compression check, Time to go play at the lake. Lake Powell, UT.