For those of you that are bolting a Carter HV pump (model M4889) to the stock botton - are you tapping out the supply and return to make them bigger? They are only 1/4" lines. (I've got two of them sitting here in front of me).

TTT

The Merc mechanical fuel pump used on the HP465/HP500 is the exact same pump used on the SC600. That ought to give you some idea of the amount of HP it is designed to support - and it does it through 1/4" fittings. If it's not working there may be something else going on...

Be sure that there are no air leaks in the fuel line/pickup within the tank that prevent the fuel pump from sucking fuel only from within the tank. Many tank/pickup assmeblies leak air where the pickup meets the fitting within the tank preventing efficient operation of any pump.

Kenny,
I have a pair of 540's and was using the a Holley mech fuel pump part #12454-11 which really sucks!---or maybe I should say they don't suck enough. Anyway the Holley's didn't work for me. I switched to a Edlebrock mech pump #1712. They have 6 valves internally vs. only 4 within the Holley. However, you must run an external fuel pump regulator on the Edlebrock. I was told to buy the Holley fuel pump regulator because they are a good regulator and work well. I have mechanical oil filled fuel guages on my dash for each engine. In other words, I have -4 braided fuel lines going from the carbs all the way up to my dash at the helm---kinda scarey, but anyway I always monitor my fuel pressure at the helm as the boat is running on plane, under load and at all RPM levels. I have not run my engines with the Edlebrock pumps yet, but my cousin had his engines on the dyno with the same Holley fuel pumps that I had just switched to late last season. The pressure on the dyno could NOT keep up---whatever the problem was the Holley's performed poorly! We switched to the Edlebrock pump while my cousin's engine was still on the dyno and the Edlebrock pump did a great job. So, I had them installed on my 540's and will be running them here very shortly.

BTW, I am running -8 fuel lines from the tank up to some new Keith Eickert coalesant fuel filter/water seperators to the Edlebrock pumps, to the Holley fuel pump regulators and each line coming off the regulators are being fed to the carb bowls. In other words, each bowl on the carb has its own fuel line from the fuel pressure regulators. -8 all the way. I'll try and post a picture of it.