Seems odd there both doing same thing. You said “ modified “ they don’t have adjustable regulators on them do they?

No, regulators are not adjustable. They are stock Merc stuff.

The fact that both motors are doing the same thing has puzzled me as well. Seems unlikely that both would have the same problem. Modifications, as far as I know, are mild. Roller Rockers and possibly some mild cams.

One thought that entered my mind, because I had the same exact thing in my Cigarette, is that the drives could have been swapped to 1.36s instead of 1.5s. I plan to check the ratio this week. It would explain why both motors fail to attain the RPM they should.

what rpm are you seeing WOT what props are you spinning ?

In my experience even if the call it a "43 psi" regulator, the newer style cool fuel regulator and pump usaually show 39 to 41 psi with no vacuum (disconnected), drops to about 35/36 with vacuum hose on, if you free rev it and let off where youve created a real high vacuum, you might even see 33/34. Under a hard load on my dyno where its actually using alot of fuel, 37 to 38 at wot isnt uncommon. When regulators bad, it almost always drops to 26 to 30 psi at idle and if you try to get on plane/hit 3500/4000 drops to 25 or less because its bleeding off all the volume, Smitty

26 Hydromotive 4-blades, with lab markings on them (boat came to me with these). Seeing 4400-4500 rpm @ 70-72 mph depending on conditions. This top speed is reached at 3/4 throttle. Feeding in more throttle causes a slight but noticeable sag in power.

TPS reads 77-78% when the throttle is at WOT. On both motors. ~4.4V if I recall correctly. I have diacom on order so I'll be able to do some real data logging soon.

Thanks Smitty, so if I'm understanding you correctly, you don't think this situation is indicating that I'm short on fuel?

Then something isn't right if this is the case. Odd it is both motors though, something likely setup wrong by whomever "built/tuned" the motors and was copied on both.

First, I'm not familiar with that cool fuel setup.

I don't know how a fuel pressure regulator could be regulating pressure after it? Just because you had x pressure before means nothing after. The higher the duty cycle, the lower the pressure to the injectors would be.

Unless I'm missing something?

Diagram of system is below.

Fuel pump sends pressurized fuel to fuel cooler. Fuel cooler has regulator mounted to it to bleed off excess pressure back to filter head. Other outlet of fuel cooler goes to fuel rail.


https://cimg5.ibsrv.net/gimg/www.off...bef04190d2.jpg

Yeah, it's a little frustrating. Non adjustable TPS so it's got to be some sort of table in the software converting the voltage to %...