Today warm up engine then ran in reverse gear to 2550rpm. Steady no issue for 5-10mins. Throttle up to 3000rpm. After couple mins rpm starts waivering. Push throttle up, rpm goes up then drops. Left at 2500rpm in reverse gear, unable to steady in rpm.
So probably I still have air trap in fuel system or I should put in a brand new fuel lift pump.
Probably try clearing air trap first.
Any thoughts anyone?
Ken Y
Yes, I do have some thoughts--but they are the same thoughts I shared before.
I had the identical problem on my 1GM. It was bedeviled by getting in tiny air leaks. It would run seemingly fine--sometimes for over an hour, sometimes much less. The symptoms were much as you described.
I spent HOURS messing with bleeding and rebleeding, checking connections, redoing connections, running the engine only to have it fail in half an hour, 20 minutes, 45 minutes, etc. etc. I finally said to heck with it! I'm going to start from the tank and just redo the entire fuel delivery system. This took much less time than all of the prior nonsense I (and you) did.
I solved it by ditching the mechanical lift pump (unhooking it, actually). I switched to an electric Facet pump, which I plumbed straight from the output of my 10-micron massive Racor 500 directly to the high pressure injection pump. In doing so I also eliminated the dinky on-engine fuel filter because it was an unnecessary point of failure. (On the 1GM, anyway, the on-engine filters can develop tiny cracks at the bleed screw.) I also replaced all my hoses while I had it all apart (though I don't think the leak was from the hose connections).
The system is now as follows:
Tank --> Racor 500 --> Facet electric pump --> Y-valve -->
Output 1: Straight to high pressure pump.
Output 2: Taps into injector return line
I also fitted a switch in the engine compartment so I could energize the fuel pump from down there.
This setup is really slick. It allows me to prime both the filter and the engine with ease.
To prime the filter: Switch to Output 2 and energize the pump. It fills the filter while passing the fuel back into the tank. You can tell when the filter is primed by listening to the sound of the pump, which slows down when the filter is full and no longer sucking air.
To prime the engine: Switch to Output 1. Crack the bleed screw on the high pressure pump. Energize the switch. When solid fuel is coming out of the bleed screw, tighten it and then shut off the switch. Done.
There are so many advantages to this system, but I'll not take the time to list all of them. To mention but a few: (1) Removes failure points. (2) Ease of bleeding. (3) Ease of priming filter. (4) Racor 500 is SUPER easy to change, even in a seaway, without spilling fuel. Filter elements are cheap (once you spring for the more expensive Racor 500 itself). Massive capacity. (5) Mechanical lift pump priming lever doesn't work worth a darn. That's now eliminated. (6) Mechanical lift pump diaphragm can fail, putting fuel in your crankcase. That failure mode is now eliminated. (7) Eliminating on-engine filter is one less filter to change.
[Note: There is, of course, no reason that you *have to* go with a large Racor 500. You can keep whatever filter you've got and still do this conversion. But I highly recommend the Racor 500 for our engines for the reasons stated.]
I'll leave it at that.
!
