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.

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Your pump is a positive displacement pump that is rated by Holley as 67gph at 5psi. Free flow is rated as 97gph at close to zero psi but that also means zero vacuum at the pump inlet.

If your fuel system was operating correctly, you should never see less then 5psi at the carb inlet unless you have raw gas coming out of the engine exhaust which would then be a carb problem..

What  this means is that you apparently have had a problem for an extended period of time that is getting worse. I suspect that if you put a vacuum gauge on the fuel pump inlet you would see around -15in.. of vacuum. This is the hairy edge where the pump will be cavitating.

Somewhere between the fuel pump intake and the bottom of the gas tank, you have a serious restriction. Lee's idea of the anti-siphon is a good idea but I would also extend that to some foreign material that is partially blocking the free flow of fuel in the suction tube. The anti-siphon is designed to work with minimal vacuum at the ant-siphon port. If there is vacuum present at the device, it will bleed air at a much greater rate then what the system was designed for.

Pieces of rust like to get caught in the tubes and will act as a point to collect other smaller particles that would normally pass through to the filter but instead get caught and start to create an even greater restriction under load. When the engine quits or is shut off, A lot of this debris will fall free until the engine is re-started and it all gets caught again.

I would try running a wire up through the tube and see if it can go all the way through.

Matt Cowles said:

Thanks all!

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.

Ronald. The vacuum gauges on the racors are reading zero at high speed Which is why we were checking all other avenues. But in my mind the guage is suspect.


I would agree. Unless the gauge is verified to work, it should be suspect at this point. Nothing worse than a gauge that is defective.

The fact that Matt is getting gunk on the fuel pump strainers tells me that all is not well with the Racors. The suggestion by multiple people to bypass them is probably the prudent thing to do at this point and see if this is a multiple layer problem or just one problem.

Captain  Matt ..........  did you check the anti siphon valve at the fuel tank line ?  that  is a designed air leak of approx. .oo7   ?   That  air leak must be plugged when converting to electric pumps  .  Your  Holley pumps are a bit  low for gph .  The  mechanical  pumps  for the 427  were rated at 120 Gph  ,  a big difference from the electric pumps you have .  You are heading to uncharted water by running to lean !   More  gph is better. 



And the answer is...anti-siphon valve. 

Since the primer bottons for my carbs are in the engine room, I could test everything without leaving the dock. First I needed a baseline, so I disconnected the fuel line to the starboard motor, started the stopwatch on my phone, and held the primer button until I reached a line on a little bucket I had. Righty gave me 32oz in just under 15 seconds. Empty bucket back into the tank...

Great, now onto the port side. Same thing...disconnect the fuel line at the carb, start stopwatch, and hold the primer button. I got a good burst at first, but by the 12 second mark, I barely had 5oz. It just sputtered and spit with and occasional burst. To quote a famous Commander curmudgeon, “like an old guy trying to take a leak.”

So next, I bypassed the Racor and tried it again. Same result. 

Went to the top of the fuel tank, and found the anti-siphon valve. This was the obvious problem as there were little bits of what was probably solder, and the normal gas goo. Before running out to replace it, I put a normal nipple on, and tried my test again...whoosh! Fuel like crazy! So off to the store, bought two new anti-siphons, cursed whoever designed the placement of those on the 35, and put Humpty back together with new valves for both sides just to be safe. It got too late to do a test run, so that will be tomorrow, but I’m anticipating good results. 

Planned changes:

- Fuel pressure gauges will be run to the helm so I can see them at all times. 

- New, lined fuel lines (I’m sure my old rubber hoses and ethanol aren’t getting along)

- To Tim’s point, I’ll be closely monitoring said pressure to assess the need for a more powerful pump. I want these girls to get what they need, so if it’s means going to the next size up pump with an adjustable regulator, so be it. 

Thank you all for your help. It means the world to have access to all you guys, and when I can post a problem and get a bunch of helpful responses in addition to phone calls from brainiacs like Dick, Lee, and Tim, I know I’m keeping good company!

Will report back again tomorrow after seatrial. 

Great to hear you found the problem. Are these a standard/easy to find item? This post has got me thinking. I replaced the engines in my 360 commander last year. I think it might be worth replacing mine. 454 crusaders w/edelbrocks and electric pumps. Still babying her, so this may not have shown up yet. Doing the senders this week, might as well do both. I think I have good access.

Very easy. I normally frequent my local boat store, but they were closed by the time I figured out what was going on. Worst Marine had several in stock - $18 each. 

Steve V said:

Great to hear you found the problem. Are these a standard/easy to find item? This post has got me thinking. I replaced the engines in my 360 commander last year. I think it might be worth replacing mine. 454 crusaders w/edelbrocks and electric pumps. Still babying her, so this may not have shown up yet. Doing the senders this week, might as well do both. I think I have good access.
Thanks Matt. I think I'll do it for the peace of mind. I'm gonna be in there anyway.
Here is a # for you. I have no connection to this business but they did a great job for me and they are pretty hard to find. They cleaned my gas tanks and filtered all the fuel in them. Northeast based, so I don't know how far he will travel.
Fuel solutions 978-423-5306. My old tanks look like new inside. He went through the sender, so access was easy on mine. Good luck and enjoy the rest of the boating season.

I noticed that Matt didn't chime in with a picture but here was his problem on the fuel pressure drop. These pieces were lodged in both the Fuel shutoff valve and Anti Siphon valve. They are Solder or Wire weld bits from inside the fuel tanks that were built about 8 years ago. Just wanted to add the picture 

Thanks Lee! I got so excited about thenboat running again, I forgot to close the loop here.

Of course the victory was not without some drama. Went down for my seatrial and had a couple small things to double check. Sadly, I left the ignitions hot while I did this and burned out my starboard coil. No damage is worse than those that are self-inflicted wounds.

Then once I replaced that, and was finally on seatrial, the port engine suddenly died on me and wouldn’t restart. My heart sank. Once I went through and checked everything, it had just been my cell phone that slid off the helm, and bumped the key just enough for it to kill power but still look like it was “on.” Had to laugh at myself on that one!

But once all that was cleared-up, had a great pair of runs this weekend down to our favorite spot. Fantastic weekend, and the old Battle Wagon fully cooperated!!

Thanks again for everyone’s input here. Always appreciate you guys!!


This was a most informative and interesting discussion!

Two questions: Why would fuel starvation damage a piston? 

And, do you remember our discussion regarding my Port Engine not staying Synchronized after running on plane for a couple of miles?  I think I called it "fluttering" but this "Bobbing" sounds awfully close except not as severe as described here.  I'm only talking a few RPM's, just enough to not stay in Sync.  BTW, both Distributor Caps are working great!  The one I modified originaly and the one you sent me.  I don't know how many hours but no problems.  I haven't heard much from the forum about other folks switching over.  Have you?

All the best,

Tim G.

Dick Morland said:


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.

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