My Performance boat has lost 4 MPH in Top Speed Pls help me diagnose the problem
06-29-2018, 10:59 AM
#91
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The above info is from Raylar in reference to 50psi on a HO525 setup. Even though you set 50psi pump on engine off, you will not see a steady 50psi when running though it will be close.
You always set fuel pressure with the vac. line disconnected. Your fuel pressure setting should be set a 50psi and you don't need any addtional pressure than that. Your fuel pressure at 3500 rpms under load will probably be around 47-48 psi. Your air fuel settings are just fine. In all the 103 kit equipped motors we measure about 12.8 to 13.2 in that 3000-4000rpm range which is right where Mercury sets them to run on a stock 496. You will see that the air fuel ratios will drop between 4000-5000rpms into the 12.4 to 12.8 range which is right where they should be for a balance between power and slightly safe side.
07-02-2018, 10:57 AM
#93
Hi John, I think that you have a different version of the cool fuel system than I do on my engine. I only see the 2 filters on my gen 3 cool system the normal looking fuel element filter and then the white membrane disc filter.
07-02-2018, 11:04 AM
#94
Update: So I was able to find the disc membrane filter and had my mechanic go out to the boat with me yesterday. It appears that was causing the issue with the fuel pressure going down when I gave it WOT Throttle. We ended up setting the fuel pressure at 53 with the engine not running which gave us 48 PSI at the lower rpm and cruise speed ranges and then got 50 PSI at WOT. So I'll check with Larry on these numbers but I'm no longer below 48 so that should be good. I may have to dial it down by 1 or 2 but I will run the boat this way today to see how it performs. Got very crowded out on the water very fast yesterday as it's been in the mid 90's here temp wise.
