On the last trip to S.C. the vapor lock problem seemed to be getting worse, and last weekend I couldn't get gas to the carb at all, so after some diagnosis and talking to Steve, I got a Mr. Gasket 4-7 pound in line pump. Did a test run before final installation and it starts and runs perfect. Now I just have to bolt it to the frame and run the permanent wiring and we'll be ready for Valdosta Bike Drags next weekend at South Georgia Motorsports Park.
I installed it just in front of the selector switch, which is a ways from the rear tank, but it primed in about 2 seconds so I'm sure it's OK.
Steve mentioned by-passing the mech pump but isn't that where the overflow return line originates?

Danny you are right about the bypass. On the earliest versions there was no bypass from the pump. Later ones had the return line off the pump as you found. This was an attempt by GM to reduce vapor lock in the long suction line from the tank to pump. By using a return line, the circulating fuel was less likely to boil. (I thought yours was the earlier style.)

You can still bypass the mechanical pump if you want to. Doing so would simply abandon the return lines. Since your pusher pump has the pressure regulator built in, the line is under pressure, unlikely to vapor lock.

The other argument concerns the possible failure of the engine pump. The rubber diaphragm is the most common cause of failure. In the standard arrangement when the pump fails you know it (insufficient fuel, suction leak) With the pusher pump, it is possible for fuel to be pushed through the fuel pump into the engine crankcase without knowing, very bad for engine. (Usually they leak externally as well so you do get some warning)

I bypassed my pump and abandoned the return system without any problem. (As it turns out, when I went to the recirculating fuel injection system I had to return it to service, but with the QJet it was fine.)

PS sorry I didn't get back to you last night, got tied up here.

Thanks Steve. I'm still unsure about the overflow if the pump just keeps on running, so for now I'll just run it through the mech pump and see how it goes. Didn't have time to work on it today but tomorrow I'll finish the install and test drive it. Then I'll see if I can figure out the fuel to the Onan problem.

My Carter rotary fuel pump runs whenever the ignition is on and there is oil pressure. I use a Mercury marine switch to do this. It goes directly to the carb.

I have towed our 4WD SUV up some steep hills at 100 degree temps with no vapor lock. Heck, even the genset vapor locked, but not the coach itself. My backup plan has been to use a higher pressure pump and a regulator right at the carb, but it has not been needed. A return line is good because it increases the volume of fuel going through the line so it can't absorb as much heat as it rushes through the lines.

I should add that a little heat shielding in the area underneath where exhaust heat can affect the fuel lines can be beneficial.

I understand the concept of wiring it to the OP sending unit, so if you lose OP the pump stops, but without pressure at start-up, the pump won't prime the carb. Probably not a problem if you run every day, but if the coach sits for a month or so it's going to need a shot. Steve mentioned a push button on the dash for this purpose, but that's a little complicated for this simple mind to figure out. I was going to wire it to a keyswitched hot spot with a toggle in the dash so it could be turned off if I needed the switch on but the engine not running for some reason.

Danny if you install a relay to be activated with your starter that applies power to fuel pump you will be fine.

The PO of my barth put a switch on the dash for the electric fuel pump . so , I flip the switch before turning the key for ignition . this lets me turn the key on (without the pump turning on) to listen to the radio . Bob

I did the same thing today. I used a lighted toggle so if it's on the handle lights up red. The hot is a switched circuit, not sure what, but it works perfectly. In the 12 or so years I've owned this coach it has never run better.

quote:

Originally posted by Danny Z:
I was going to wire it to a keyswitched hot spot with a toggle in the dash so it could be turned off if I needed the switch on but the engine not running for some reason.

That works for start up, but in a collision, the engine is likely to shut off, preventing a fire from the fuel pump keeping on running. A better set up is a collision/impact fuel shut off. My Jags have have all had them, and I like the idea. But, so far, I have not put one on the Barth.

The 6.5L TD in my coach has the oil pressure switch for the lift (fuel) pump. I would guess that the same would work for gassers.

Just convert your carb to a fuel injection system and the computer will turn the pump off for you!

Of course, you'll need the injector body, adapter, new distributor, fuel pump, MAP sensor, coolant sensor, O2 sensor, throttle position sensor, and harness, but besides that, it would be a snap!

Plus the cost of Steve installing all that.

I have a two electric pump set up with an oil pressure switch. It does take a few seconds of cranking to get the oil pressure to ground the relay after it has sat for a while. It has never been a problem and I think it prevents unnecessary wear on the engine from starting with no oil pressure after sitting. I thought of installing a momentary push button switch but like it like it is. It may have saved my engine when a oil cooler lines failed and I lost my oil. I dont know if I would have noticed the oil pressure gauge in time.

NT

quote:

Originally posted by Neil T.:
I have a two electric pump set up with an oil pressure switch. It may have saved my engine when a oil cooler lines failed and I lost my oil. I dont know if I would have noticed the oil pressure gauge in time.

NT

A BB chevy gets serious lifter clatter when a line bursts. I experienced this in a boat with open exhaust but a covered engine. I suspect one would hear it in a motor home.

Having said that I use a pressure switch, too. My Barth needs to be cranked anyway to fill the float bowl. The fuel seems to evaporate overnight.

Another way to go is to use a regular idiot light switch to illuminate a really bright idiot light or (better yet) a buzzer or horn. I did that on a racing dune buggy to be sure that it got my attention in the middle of a whole bunch of noise and activity.

I have an LED bar across the top of my dash that Lenny gave me. It's wired to the idiot light sensor and is very bright. With a splitter from NAPA I was able to retain my gauge also.