Wide open throttle bog
 

Hello all. I have learned so much from this forum. I have a 96 z240 7.4 mpi bravo 3 28 pitch prop I've replaced the fuel pump, check valve, drained tank, replaced fuel filter several times and at wot the boat bogs like its starving for fuel. runs perfect otherwise. I've also blown air down pick up and in vent. All seems to be clear. I'm starting to lose hope. Any help is greatly appreciated. I bought this boat last summer and love it. Just want to work out what i think is a small problem. I can get about 4K rpms before it bogs. I also noticed out of water hooked up to hose when you romp it it stalls at around 3,000 for a split second and then revs up full throttle so quick you have to be ready to pull it back. Had it out yesterday and same thing. Last summer it would run WOT no problem but sometimes the lines would lose prime. I got tired of sucking on line so i installed a bulb primer. I took it off today and ran straight line. Thanks in advance

Re: Wide open throttle bog
 

I had this problem several years ago in another boat and the problem was the fuel lines. Over time they deteriorate and can collapse due to the suction of the fuel pump especially under heavy load. Out of the water there is no resistance for the motor so it will rev quickly and should be avoided. Marine fuel lines are dated and it is not unusual to change them every 5-7 years. Hope this helps because it is a relatively inexpensive fix.

Re: Wide open throttle bog
 

thanks
yeah I've replaced the lines from tank to filter. The rest appear to be metal lines. This is driving me nuts

Re: Wide open throttle bog
 

I had a similar problem with my 272 w/ the 502 MPI. It would develop a "bog" which became especially noticable when under a load. I found the problem to be a burnt spark plug wire. The boat was in need of a tune-up so I replaces all plugs, wires, cap and rotor.

I also changed the prop for one with a bit less pitch. I went from a 23 - three blade to a 19 - four blade which made a TON of difference out of the hole. A 28 pitch prop for your boat seems a bit aggressive which may be contributing to the top end bog you are experiencing.

Just though I would throw these out there!

Re: Wide open throttle bog
 

I found a guy online who told me to check vapor pressure tank filter. It primes the fuel rail. Pulled it off today and it was nasty corroded! Seems to rev better on hose. Before would stall for a split second at 3000 rpms before it would rev up. Not any more. Hopefully on lake soon and see if it's fixed!! Thanks for the feedback gang!

Re: Wide open throttle bog
 

Just for my own information where do you find the vapor pressure tank filter. My boat runs great but you never know what tomorrow might bring. I have the same motor setup in a 1996 Z252

Re: Wide open throttle bog
 

Follow the fuel line to rear of intake manifold. It has 3 fuel lines and clear vent tube plugged into it along with an electrical connector. It's held on by one long bolt in from the rear that runs underneath tank.

Re: Wide open throttle bog
 

I haven't looked at it yet, but does the clear line run to the fuel pump?

Re: Wide open throttle bog
 

Yes it runs to the front of the block and T's and I believe one runs to fuel pump on mine. I have the fuel pump belt driven with sea water pump. Removing and cleaning was fairly easy but be careful because I was told strainer filter not available anymore and the O- ring for tank will swell if you get carb cleaner or anything like it on it. It's only offered as a kit and it's a hundred dollars!! I was able to get mine back together luckily.

Re: Wide open throttle bog
 

Thanks. The more I find out about working on my boat myself the better I will feel on the water.