Here's Johnny

here's the scenario....... I start both engines.......warm them up for a few minutes......idle for about ten minutes till I get out of the no wake zone.....I push on the throttles......boat begins to come on plane.....at around 2500-3000 rpm the port engine stops gaining rpm.......very eradicly gains and loses rpm while stbd. engine keeps climbing up with no problem........port lagges behind quite a bit then shortly begins to climb......boat gets on plane and runs fine.........come to the next no wake zone......idle for 2 minutes.......go to get on plane again and both motors maintain exact rpm..........problem gone........

I have changed all fuel filters numerous times.......could this be a mechanical fuel pump? keep in mind this engines fuel pump is only 1 season old...... Could it be airbound and I need to bleed air out of the fuel system? Could it not be a fuel problem ?? Thanks in advance guys........

Steve Zuckerman

My (575 Merc/Eickert) mechanical pump diaphram was eroded by our E10 fuel over the winter. I would check the FP oil reservoir for trash and fuel. Mine had gray junk in it. Rebuilt it and everthing seems OK.
It's also hot as hell down here. Several boats had warm starting problems this weekend due to fuel vaporizing in the lines.
Could also be a coil going bad. Sometimes they are erratic before giving up the ghost completly.
Regards,
Steve

Here's Johnny

What was the engine doing that led you to diagnose the bad fuel pump....... my gut is telling me that is what the problem is.....

Shah Mat

How about the ignition? My buddy has 575's and he had a similar problem. Turned out to be the firing pin the touches the rotor thats on the inside of the dist cap.

Here's Johnny

ran the boat yesterday.......very very slight hesitation 1st time coming on plane.........the next 3hrs the boat ran like a raped ape......go figure.......

Steve Zuckerman

Nothing. I found junk in the fuel/water pump oil reservoir when the motor was out to change couplers.
I rebuilt the pump (new seals, impeller, and diaphram) since the motor was out and it was easier to get to for service.
It would have split the diaphram and reduced the fuel pressure had I run it. If your fuel pressure is low on the motor that's acting up, there you go.
Steve

Vinny P

John and I went to his boat today for a mechanical inspection and a test run. I scanned the engine for codes, none stored, all the sensors showed good. I pulled the distributor cap and rotor, looked like new. When I was screwing around removing the cap, I saw the MSD 6 boxes. I forgot all about them. I am thinking that the box may just be starting to break down. We went for a ride, with the boxes hooked up, hoping to get it to act up. Ofcourse, the engines ran fine. When or if it happens again, we will by-pass the MSD and run the ignition without it.

CSCinc

do you run a rpm limiter on the msd. Had a motor acting up and pulled the chip out of it and it ran fine..... jus something else to try

Vinny P

No, the MSD's dont have a rev limiter. The engines rely on the stock limiter in the Merc ECU.