Alright boys, I need some help, ideas, maybe an exorcism at this point...
The system: 427’s, Holley (red) electric fuel pumps, Racors before the pumps, fuel pressure gauges at carbs, Edelbrock 1409 carbs. Electronic ignition with rebuilt distributors with new Pertronix units. I’ve put about 12 hours on this set-up without any sign of what’s currently happening. Tanks at about 3/4 full (filled-up last weekend).
What’s happening: On Friday start-up and idle was normal, and did about 10mins at 1000RPM to open water. About 20mins after getting up on plane, I checked my fuel pressure. Starboard side good at about 6psi, but the port was reading 0-1 psi. Shortly thereafter, the port motor started “bobbing” from our 3000RPM cruise down to 25-2600. “Bob” is the best description as it was like the fuel pump was cutting in and out. Come down to 1500, everything smooths out, and fuel pressure returns. Try to run up again, and the pressure drops again, and shortly thereafter the “bobbing” comes back.
What I’ve done so far:
- Tried running with the fuel caps open.
- Tried running with crossover opened.
- Instead of quality family time at the pool, I spent Saturday changing the fuel filters, disassembling and cleaning both pumps (there was some gunk in the pump screen), and swapping them (port for starboard).
This Morning: Start-up, idle, and 1000rpm to open water was flawless. Did fine at 1500. Went to get on plane, and within a few minutes, the “bob” returned. It would let me run for short periods of time at about 2700, but then wouldn’t even allow that. Required we finish the last hour at 1500 to get home.
This afternoon: Knowing valves can cause weird power issues, I checked those while they were hot. Also confirmed timing was good. Then I swapped the carbs. At this point, I fully expected the problem to switch over to the starboard engine (thereby making the carb the culprit). But it didn’t. The port motor yet again responded the exact same way.
So now what? It’s not the carbs, fuel pumps, or filters. I also don’t think it’s a problem with the crossover or siphon as the motor responded the same way with every combination of open/closed.
Please help. I’m approaching the end of my pitiful rope.
If it was a ground issue, wouldn’t it be misbehaving all the time and not just above about 2000RPM?
And the temps are within a degree between the two pumps. Good suggestion, though, that was one of the things Holley suggested too when I talked to them yesterday.
I don't like the pump downstream of the filter, just one more potential problem. With the volatility of the fuel and warm engine room a weak pump may find difficulty. Almost all pumps are happier with flooded suction. Can you bypass the filter?
Matt, last time I used an electric pump was late 1960's. It built to pressure and the clicking of the pump would stop. Is that the case with yours and if so does the offending pump quit clicking, key on engine off? If so it may or may not be the problem but if it continues to click even occasionally it could have been damaged running nearly dry. Just musing, no expertise.
The Red Holley is a gear pump that runs continuously. It also has a strainer in the base on the inlet side that you might want to verify is not plugged. One problem with this pump as Tim mentioned, is that having the filter in front of the pump does allow for vapor lock-cavitation issues, especially with the fuels available today.
As far as the 100 micron filtration level, that is very wide open. Standard hydraulic system metal strainers are rated at 40micron and a good pleated filter will get you to 10micron but be susceptible to rapid plugging.
Racor rates their primary filter element at 30microns and offer secondary elements all the way down to 2 micron.
I tend to agree with your thinking that an electrical power issue to the pump would likely occur at more then just the higher fuel flow periods, especially on this particular pump as the current draw will actually decrease slightly as the pressure drops
So here is a question, "If you have the Racors between the fuel tank and the fuel pump, how is it that you had gunk on the pump inlet strainer?" This tells me that all is not well in the fuel filter portion of your setup.
Either the element is not seated properly and allowing fuel to bypass around the element or you have some internal issues with the filter. The o-rings are also problematic in a filter before the pump setup in that a bad o-ring can experience a vacuum and allow air to enter the system which would give you the symptoms that you are experiencing.
The gunk on the pump strainer also suggests that you might also have gunk in your fuel tank. Was the gunk on both pump strainers or just the port side pump?
I suspect that there is something not right on how the port side Racor is put together. Since you tried the crossover with no effect, that tells us that the problem is probably not in the fuel system up to the crossover valve.
Tims idea to bypass the port side Racor is a good one in that it would positively determine if the problem is in the port Racor filter. I suspect that you will find that it is in the Racor.
The Racors also do have an internal check valve that can become partially plugged that is on the inlet side of the filter. To get to this requires totally disassembling the bottom portion of the filter.
I think you will find either a bad o-ring or else an obstructed inlet flow on the port Racor.
You're getting some good advice here, but let me add a couple of things. Any old drag racer can tell you what can happen to an engine under heavy load (like planing a heavy Commander) that starves for fuel due to a fuel delivery problem. Once it starts to "bob" or stumble, your pistons are in mortal danger. If it would have been me seeing 0 - 1 psi of fuel pressure I would have immediately taken this engine down to 1200 rpm or so and would not take it anywhere near planing rpm till I had found the problem and could observe a nice solid fuel pressure at least above 3 psi. I think you're really lucky you got away with loading up an engine that obviously is starving for fuel at higher rpm's. I agree with Ron, I don't like filters in front of gear pumps. Who told you these pumps pull better than they push? It's usually the other way around, which is why most electrical fuel pump installations are close to the fuel tanks. BTW, what is your port engine fuel pressure at lower rpm's not under load ? You can check this at the dock. It should be about the same as the stbd. engine. Do you still have the Carters so you could do a temporary swap ? I have a few other thoughts, but save these old arthritic fingers some keyboard pounding. Give me a buzz.
At least it seems like we’re narrowing in on how to continue to close the scope of the problem here.
I did mean “push rather than pull” when I mentioned the pumps earlier - typo.
Overall, perhaps I’m too focused being the same set-up I’ve run fine with (aside from a piston breaking apart) for 4 seasons. Just with different pumps. Those Carters were pretty beat-up, so they both got tossed when the one failed.
Ron - I didn’t consider your point that with me filtering better than what Holley recommends, I should find absolutely nothing in that’s screen inside the pumps. Yet both pumps had some stuff in there. Certainly points to those Racors. The only other difference to this whole set-up that I didn’t think relevant but maybe could be a contributing factor is I’m currently running my second tank of Valvtect Octane Boost. I wonder if the Racors, having never been exposed to this stuff, is part of the problem.
Dick/Tim - Definitely sounds like I may need to reconsider the overall set-up here with the next step being a full bypass of the Racor. Fuel pressure under load is 6-7 at idle, about 6 at 1000, 4-5 at 1500 (I will note, at this point the port psi will flutter a bit, but usually levels out I always figured it was the gauge), then be in the 3-5 range at cruise. But now that I think about, that’s low for these motors, isn’t it? Shouldn’t that be closer to 6-7 given the pumps capacity and engines need? Good lord - has this set-up been starving these motors of fuel all along?
Dick, I had every intention of giving you a ring, but didn’t want to bother you on Sunday. Will call today.
Good Morning Matt
I consulted my son on this, as he is a mechanic and is familiar with electric fuel pumps. His first thought is a fuel supply issue. He would start at the pump and work back to he tank checking fuel lines, and the in tank pickup. Having the pressure drop under load is typical of a fuel supply issue. Also if there are any rubber lines in the fuel supply, change them. E10 deteriorates the rubber and it could be collapsing under load. His opinion was that a voltage drop would likely show up all the time, not just under load. Checking this with a multi-meter at he pump would be his second choice. Hope this helps.
Anybody think it could be a Bad/Restricted Antisiphon? I would either bypass the racor or if that makes you nervous Run the line to the other racor. ( He has twin engines) and test run. that would rule out the racor. If you run a line to the other racor, it would rule out tank supply. This screams of supply issues.
Thanks as always, Lee. And thanks as well for letting me pester you earlier on your day off.
Tonight I intend to check for an anti-siphon on the tank and bypass that Racor entirely and see what she does.