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Along with lugs/cable size upgrades - it's best to NOT use the engine for the harness/panel ground because heat / terminal and fastener expansion-contraction /corrosion can cause issues.  It's best to run the battery neg cable to the starter bolt (so current goes directly where it's needed), run a heavy alt neg cable to that bolt, and jumper to a buss for (harness and other) lnegative connections directly to the battery cable.  It could jumper from either the starter bolt or Alt neg post.
The battery neg cable on the bell housing is not the best location.

That makes a lot of sense and most likely contributed to the issues I was experiencing. I don't believe my starter has an official ground terminal.
There are two bolts and two screws on the forward side of the motor housing. Which would be best?

Would a grounding bus in the engine bay be a good option, have one place for all of the grounds to land?

My boat came w a dedicated emergency/start battery as bank 2 and a large 4x 6v as bank 1, but I still suffered from slow start under certain conditions (esp when the engine was hot) that I could not diagnose, even when using the fully charged start battery.

I replaced my engine compartment wiring harness connector strip and restripped the wire ends in the process, which improved the glow plug current and start signal.
The fuel pump and fuel gauge would still occasionally flutter, which turned out to be the engine block ground, which had a poor crimp connector and was undersized. The original #4 awg wires were copper only, not tinned.

I replaced the starter positive, alternator positive, and engine block ground with #2 awg tinned copper and high quality crimp connectors, and now absolutely everything works properly under all conditions: fast crank, quick start, and higher current flow when charging.

I had slow crank and intermittent start issues as well.

It was definitely my engine block ground. Once I replaced that, no further issues.

My throttle controls 'slip back' at higher rpms.

Up to ~2300 rpm, the throttle lever stays where I put it.
It will rev higher, but will slip back to ~2300-2400 with the throttle lever physically moving back over a few seconds.

Would love some suggestions where and what adjustments/inspections I should make to resolve this.
Is it the cable itself, the lever at the binnacle, or some other adjustment?

Edit: Seems it can be fixed either way as per KWKloeber's link below. Either tighten the friction screw for the lever in the binnacle or add a 1/4" clamp to the throttle cable in the engine-bay to increase friction. One requires compass removal, the other is easier to adjust in the future. And when I went to install a clamp on the throttle cable, I discovered there was one in place already. I tightened it a smidge, and now my throttle holds all the way to WOT.

@J34 The REG terminal is for the red wire from the internal regulator (looks like it's hanging down inside the case???)

Ahh the old alternator is not wired properly: the red wire from the regulator should be on the Reg terminal. I had taken it apart to see if I could find the problem, saw the diodes visibly cracked, but when I put it back together, I didn't refer closely to my original pictures because I wasn't going to install it again. Sorry if those pictures confuse anyone.

I blew the diodes on my 1988 M25XP 51a Motorola, which is fine: it had a wobble in the shaft and has done its duty.

(I mistook the Reg terminal for a Voltage Sense terminal, and it didn't like that. If someone could explain what that Reg terminal is actually for, I'd appreciate it.)

I ordered a 51a replacement on Amazon from RareElectrical for $165, needed to get one quickly for vacation next week.
I also ordered the 105a replacement and a new pulley from catalinadirect for $210 because it comes with the 2" adapter, but it won't arrive until Monday. I could not find a direct-fitting replacement 90a or 105a on amazon. I expect I will install the 105a and return the 51a.

The new one pictured below has the same connections as the factory with the addition of a sense wire. The one from CD does not have a sense wire, but does have a voltage adjustment on the regulator to compensate for longer cable runs.

Here are some pictures of the two side-by-side.

My house bank is 4x 6v 230ah. We have a 12v fridge, 1500w inverter for a 700w microwave that we use frequently, 12v fans that run many nights on the hook. We also have inflatable paddle boards that pump to 15 psi using a 120w pump. There have been mornings where the house bank did not have enough power to start the engine.

Any thoughts or observations? Should I wait on the 105a from CD and use it?

I used 1" hose and a marelon 1" barb to 3/4" npt at the seacock because it has a large opening all the way through

Just to be precise it must be something else -- Forespar doesn't manufacture a 1" x 3/4" NPT Marleon hose barb.  Nor a 1" x 3/4" tailpipe (w/ straight thread to fit the valve.)

Right here: https://shop.hamiltonmarine.com/products/pipe-to-hose-marelon-tailpipe-44618.html
And here: https://www.fisheriessupply.com/forespar-tailpipes-hose-adapters-tapered-pipe-threads/910160
And here: https://www.forespar.com/product635.html

FOR-910160

I used these: https://smile.amazon.com/Forespar-Drain-Degree-Plastic-Flange/dp/B0942NDKB8

The upper piece goes between the drain and the tailpiece nut, and the lower part threads over the top part.

Gives you 1" hose barb. I used 1" hose and a marelon 1" barb to 3/4" npt at the seacock because it has a large opening all the way through, larger than the bronze groco equivalent. Used a 1" wye to combine the two sinks' 1" hoses.

My drains are so fast.

All of the original ones in my 1988 do not have base flanges, only thread onto the thruhuls.

There are equivalents w base flanges that you can buy if you want to confirm to modern standards when doing replacements w backing plates.

All of my original marelon seacocks work as new.

I didn't have a single issue after polishing the pump housing cover: several engine starts, one after some pretty serious heeling and waves.

I have also been starting the engine with 1/4 throttle, so the pump is spinning faster initially.
Maybe that makes a difference, maybe not.

Either way: seems like everything is working properly.

Thank you all so much!

Three of my blocks had come down. I glued them back up w 4200, and they've been happy ever since.

The inside of the pump cover was not clean: had residue from the impeller.
I cleaned and polished the cover w a series of wet sanding pads, first to remove the deposited rubber and then to polish the surface.

I confirmed that the impeller has not separated from the collar: it will not turn without the pump shaft also turning, so it appears the impeller itself is good.

When operating at idle in the slip (which was not a problem in the past), it seems to me that more water is coming out the back, so the impeller seal seems to be the most logical explanation.

Thanks for the advice, and I am sorry for creating yet another impeller troubleshooting thread. :)

I searched, but the words used to describe this are very general terms.

On several occasions after sailing and heeling, we have started the engine only to discover the raw water is not coming out the back.

The fix is to quickly loosen the screws on the Oberdorfer pump housing, which seems to let air escape along with some water. After retightening the
screws, the pump works perfectly, water emerging happily out the back.

I also tried loosening the drain plug this time (before loosening the impeller screws), and nothing emerged at all, which surprised me. Could that indicate that the impeller was not turning?

I cannot reproduce this in our slip: every engine start works without fail.
The impeller is new; the intake filter is clean.
Sailing and heeling seem to be the variable.

Please guide my further diagnosis. :)

Bumping this old thread because I found it when doing galley drain searches, seemed like as good a place as any for another option.
I was inspired by this post as well but could never quite figure out how he did the connection at the seacock.

2x Moen 2" Drain (shallowest I could find)
1x Lasko double sink drain kit
2x Plumb Pak trap kit
1x Lasco branch tailpiece (easy connection for sink drain hose)
2x Plumb Pak elbow
1x 1½" Marvel connector (convert branch tailpiece to 1½" PVC)
1x 1½" to 1¼" PVC insert reducer (convert 1½" PVC to 1¼" FPT)
1x 1¼" MPT to 1" barb (convert FTP to 1" drain hose)

Album w Descriptions

Original Drain ~2002 install. The reducers ensured that there was always water sitting in the drain.
Under the sink, the hoses came together via two separate Ts and six hose fittings below the waterline.
The drains themselves were plastic and broke apart as I attempted to remove them.
New drains are stainless and a significant aesthetic and functional improvement.


I wanted shallow drains and direct threaded connections.
By combining the double sink drain kit with a pair of trap kits, I was able to thread directly onto the sink drains w 1.5" pipe.
The branch tailpiece allows easy connection of the fridge drain hose.


The only odd part is converting the 1.5" slip tailpiece to 1" ID Hose.
The seacock had a 1" ID fitting already, and I wanted to keep that for simplicity but wanted to limit connections below the waterling.
This is my frankenpiece (daughter added the stars): Marvel Connector, PVC 1.5" Slip to 1.25" FPT, 1.25" MPT to 1" ID Hose Barb:


It doesn't look like much outside, but inside it provides a very graceful reduction to 1" hose.

Planning to plumb w white 1" drain hose, and while the real moment of truth is many months away, this is sure to be a huge improvement.

I just bought my boat, but I had an incredible experience moving it.

'Owenoke' is a 1988 C34 that was in Norfolk VA, and I needed to move her up to Worton Creek MD, ~150NM.

The first long weekend in November had an incredible forecast: lows in the fifties, highs in the sixties, and no wind to speak of. Ordinarily, the windless forecast would have been terrible, but when you have a tight timeline and a decent distance, it's exactly what you need.

My father and I drove the boat, completing the purchase Friday morning and arriving in her new slip by mid afternoon Monday. We had a wonderful time navigating fog, had breakfast with a pod of twenty dolphin in a dense sunlit mist, graced by crystal clear nights and beautiful mornings.

By definition, it was terrible sail, but it was an incredible trip and a wonderful way to begin my boat owning experience. https://youtu.be/qgtv8R4bSF8