Fuel System Priming

Looking for some procedural guidance as to how to properly prime the fuel system on my 275GTB/2. The system has been refurbished including all new hoses from the tank to the carburetors and rebuilt fuel pressure regulator and Fispa mechanical fuel pump(discussed in a previous thread on this forum). Is this done by running the electric fuel pump in conjunction with the mechanical pump or by itself until fuel reaches the carburetors and is there any bleeding of the system required and if so, at what junction in the fuel system should this be done? Specifically concerned about how much time I might need to run the electrical fuel pump and/or crank the engine before the fuel system is flowing fuel and pressurized?

Have never rebuilt this system before now and any assistance will be much appreciated.

Ed

 

Just the input I was looking for DWR46. Many thanks to you. I made one attempt at priming the system before my original post and was a bit concerned when the pump did not slow down nor change its' "tone" of clicks as you noted. Better to ask than to continually run the electric pump and risk damaging it. One other item I failed to mention in my original post was that when changing out the fuel hose from the top of the tank to the fuel filter housing, there was no filter attached to the bottom of the fuel pick up tube when I removed it from the tank. I don't believe it fell into the tank and I used a boroscope to search the empty tank but to no avail. I plan to replace this filter before using the car but at the time I couldn't help but wonder if it was more than just a filter and might have had something to do with my fuel system failing to prime. Thanks again and I'll post my results.

 

Many thanks for your advice John. I gave Dyke's method a shot first, and sure enough, the pump returned to what would be considered normal audible clicks and then slowed. I switched it off and then checked every fuel fitting connection for leakage as everything had been renewed (new hoses,replated fittings and new copper and fiber washers) and I was sure I would find something weeping fuel. Fortunately, none of the more difficult to access connections were wet/leaking and I snugged up those few that were moist and the engine fired right up. Let it idle for a minute or so on just the fuel in the carbs and the mechanical pump (electric pump switched off) until the most forward carburetor began to starve for fuel. Noted the glass bowl on the pressure regulator was only about a quarter full and I'm surmising my phenolic spacer is a bit to thick preventing the mechanical pump from creating adequate enough fuel pressure to feed the carburetors. Step one was to get fuel flowing and the engine running. Will now move on to the procedures discussed under the thread titled Fispa Mechanical Fuel Pump and will follow up in that thread once I've got the pump running properly. Many thanks for your guidance.

Ed

 

Dyke: Thanks again for your most helpful assistance. I'll run the car on the electric pump for awhile as you suggest. I noticed when I first ran the engine, it began to stall shortly after I switched off the electric pump, confirming what you've noted; that the mechanical pump hadn't started to pull fuel from the main filter junction. Locktite 518 sounds like the ticket for sealing the fiber and copper washers. Thanks for sharing that as well.

Ed

 

Ran the engine at idle for about 5 minutes with the electric pump running as Dyke had suggested, keeping an eye on the fuel level in the glass bowl. The level dropped fairly quickly to about 20% full, and with the exception of an occasional dribble of fuel into the bowl, the level never rose. The engine eventually stalled even though I kept the electric pump running. It would appear that I'm getting minimal to no fuel pressure from the mechanical pump and I'm a bit baffled why the electric pump alone wouldn't keep the engine running. Attempted to re-fire the engine after giving everything a once over and noted that the electric fuel pump is clicking constantly and rapidly, just as it did before I employed Dyke's suggestion to inject compressed air through the tank filler neck to prime the system. The engine did not re- start and I'm thinking will require an air injection again in order to prime and fire. Thinking I may have multiple issues to resolve not limited to what may be a faulty mechanical fuel pump and potential blockage/restriction (not likely) somewhere in the system. Will continue to investigate and follow up.

 

Dyke: Picked up a tube of 518 today and will carefully inspect everything and reseal all the washers on the suction side of the system. I looked the pickup tube over closely when I changed out the hose from the tank to the rear filter housing and other than the missing filter at the end of the tube, it appeared to be in good shape with no cracks. I also noticed a slight fuel weep around the tank hose banjo fitting that is secured by the pickup tube. Quite possibly enough of a leak to create the problem you are referring to. Thanks again for your time and advice and I'll follow up with my results.

Ed

 

Disassembled,inspected and then reassembled all connections on the suction side of the electric pump utilizing new copper washers and a smear of Loctite 518 as recommended by Dyke. Electric pump primed on its' own and did not require assistance via a shot of compressed air as it had before. Several constant clicks from the pump,then slowing as it always has. Engine fired right up, the pressure regulator glass bowl filled with fuel and the mechanical pump took over, running the engine for several minutes without issue. Everything appears to be functioning as it should and I think Dyke's diagnosis of an air leak on the suction side of the system was spot on. Thanks again for your assistance. Although the mechanical pump appears to be operating properly I will move on to measuring the fuel pressure coming from it, making any necessary adjustments and post my results under the thread entitled Fispa Mechanical Fuel Pump.
Thanks for your great advice Wheels1 as well. Close to getting back on the road and will certainly do as you suggest after my first long run.

 

Thanks Dyke for verifying this. I thought that might be the case when I was checking each fuel connection after allowing some time for the sealant to set up before running the engine. I could tell from the appearance and texture of the cured excess 518 that had squeezed out that it would not be wise to tighten any weeping fittings where I had used 518 for the reason you suggest. As such, I left everything alone and ran the engine. Located a fuel pick up tube filter which is on its' way here. I plan to use new crush washers and sealant when I install the filter on the tube and back into the tank. Should I find anything weeping in the future that was sealed with 518,it will be disassembled and redone. Thank you again for your much appreciated assistance.

Ed