Easiest way to prime a 12v71?

[racclarkson@gmail.com]

I took the opportunity to put an elbow in the Racor gauge so i could see it easily from the doorway. So what are we looking at? Is it vacuum created by the motor fuel pump? Motor was running at 900rpm when photo taken. Robert has suggested a gauge on secondaries but will this show pressure? If so, what should the gauge range be? Shpuld it be attached to the OUT port on the secondary filters housing?

Scott, correct, fuel pump vacuum from primary filter. 900 RPM no-load or underway? Reading appears high for 900RPM, especially so if no-load. I’d be looking at filters or line restriction. Mine typically are at, or just off, 0 vacuum at idle. I wouldn’t be concerned at all with your reading at 18-1900 RPM. But also the boat makes a difference. For example, with a nearly full main tank, my Racors will gravity fill themselves. Also correct re pressure gauge, 0-100 PSI is the range and a free out on the secondary. I’ll push 6-7 PSI at idle and 60-65 PSI at cruise. The pressure gauge is obviously useful in diagnosing a bad fuel pump once you’ve established it’s getting fuel. The gauge is also very helpful if you’re priming via a pump or a cross feed. Once you register any pressure, the air is gone and your secondary is full. You’re ready to start—no fuss, no muss.

[scottinsydney]

jmooney: There is no priming switch on the dashboard. But I was thinking of how to do the wiring for a 12 volt priming pump on each motor. I as alsso aware of holding down the STOP button to warm up the cylinders.

So I thought, why not connect priming pumps to the STOP button. For cold starts it would do BOTH the warming of the cylinders and the priming of the engines better than it might have been before. With ignition ON and STOP pressed the priming pump would work. With START pressed and STOP pressed the cylinders will warm AND the system will prime. In theory, this should work. You would need to wire in a couple of 36 to 12 volt converters for the pumps.

+++

Robert: The Racor vacuum reading was 900RPM with no load. The only non Hatteras obstacle would be the Floscan sensor which does form a restriction between the Racor and the engine fuel pump. The fuel manifold valves and Racors are 2.5' above the fuel tanks and the copper fuel lines go UP and DOWN twice before the Racors and then down to the Floscan sensor and the UP to the motors' fuel pump. Maybe this fuel routing would cause the higher vacuum reading.

[racclarkson@gmail.com]

Good points, Scott. I have Flo-Scan as well. You may be surprised to see what can come out of those cans.

[jmooney]

Keep the priming switch separate, you rarely will use it. However, I use block heaters before every start if I can . If we are going in the morning, I run them all night. My engines start okay cold ,but the effect of the block heaters is great, instantaneous start and no smoke. My racor vacuum is high even with new filters. This might be caused by the high position of the racors, but I think it’s because of the flow scans which I am in the process of removing . I will try to replace them with solid state flow meters from Maretron.

[scottinsydney]

Boat is kept on swing mooring, so no luxury of shore power to keep engines warm.

New cables from dash to engine rooms would be difficult.

[scottinsydney]

Following on...

Today I removed an excess section of the starboard engine's flexible fuel supply line to have it shortened a few feet at the hose shop. The excess hose came about after new Floscan senders were installed and created a loop in the hose. This is the flexible hose that goes to the fuel pump.

When the fittings were undone, there was little fuel in the hose. This suggests to me that fuel is somehow siphoning or being pulled by vacuum back towards the fuel tank. From cold, this engine is always harder to start and takes its time to fire on all cylinders. It then runs perfectly. Hot starts (or within three days) are instant. Problem came about immediately after the Floscan senders were replaced. All fittings are tight, sealed and I'm satisfied no air leaks.

I read somewhere the Racors have one way valves.... are they easy to check somehow?

[Chasemmc]

Scott, while you’re at it add a pressure gauge on both adapters. Very inexpensive and an easy install.

Do u have pix of guage installed?

[Chasemmc]

Oops, didn't read through to end of post. I see the pix