03 DF140 couple of questions

[Lunchmoney]

I've put about 35 or so hours on the engine since I rebuilt it. Had her 55 miles off about 10 days ago, caught 1 nice wahoo and a slinger mahi. She's been running great. Yesterday, went to take the family for an evening cruise on the local lake and noticed as soon as I cranked it up, it idled higher than normal. Typically she idles about 650 smooth as can be. As soon as it started yesterday it idled about 1100. After 20 seconds or so, I knew this was abnormal so I turned it off. I immediately restarted it and idled at 650 like normal. Any ideas what caused this?
Second thing, I'm getting what I would say is excess oil coming back through the breather hose from the top of the valve cover into the silencer. It's not excessive to the point it's even noticable on the dipstick, but I've got a few drips coming out of the throttle body down into the side cowlings. I've read it's normal to get a little blow back, but it seems a little too much. During the rebuild, I was careful to orient the new rings per the manual. Compression checked out fine. I had to put a brand new head on when I rebuilt it complete with new valves, springs, cams, etc. Cylinders were honed, new rings. Maybe I should have the valve lash checked again?
Third and final thing, This engine won't accelerate beyond 4900 rpms trimmed all the way down. The last 2-3 inches of travel in the throttle control just don't seem to have any affect. If I trim her up a bit she'll hit 5000 but that's the max. I have twin engines and the other one doesn't do this. It'll hit 5300 or so. I tried adjusting the throttle cable thinking it wasn't opening up the throttle all the way. No change. Thanks for any advice.

[Moonlighter]

First issue could just have been a bit of blockage in IAC valve. Monitor.

Second issue - no ideas, but suggest it could be related to third issue.....

Third issue - IMO you are overly lugging those engines with too big pitch props. Lugging engines increases pressure on rings.

These engines should be propped so that they can reach 6000rpm at wot, or at the very least, 5800rom with a moderate load on board. You need to find another 800rpm or thereabouts to get these engines in their optimum operating zone.

So the usual procdure is to check engine heights first, if they are buried too deep they will lose revs so lift them up if the anti-vent plate is under water at cruise speed. Then when height is sorted, then get props sorted.

See the sticky thread at top of forum re engine heights and propping.

The difference between the engines rpms could then be as simple as props not matched - even though they may be marked as same size, they may not actually be.

With twins its a very good idea to have props scanned, tuned and adjusted so they exactly match each other. Its not uncommon to see brand new out of the box props ofthe same brand and size measure quite differently when scanned.

But I would suggest you wait until you get the height sorted first as you probably will need different props as the revs you need to get are too big to get by repitching the current ones.

[Lunchmoney]

Boat is a 95 Seacat SL5C. It feels like it's bow high but I just bought it last summer so I'm still getting used to it. Sure rides and drives different than a V hull. I'll follow your advice and look at the heights first. Thanks Moonlighter, I greatly appreciate your insight.

[Lunchmoney]

Hey Moonlighter. Just to clarify, my hull is a 25`catamaran. I don't have trim tabs. Because the sponsons are so far apart and the engines, neither is counter rotating.
Ran the boat this evening and observed the following...
Starboard engine will max out at about 4900 with the port engine only about 3/4 throttle. When I max out the port engine, it goes to about 5600 and the starboard creeps up to about 5100, no more. I checked the anti ventilation plate positions at numerous rpms levels from 4k and up. They both stayed 1.5" to 2" below the water surface. Trimming up and down didn't have much affect on this. According to the specifications in the manual, I should be seeing anywhere from 5600 to 6200 rpms at wot. One engine is barely getting there and the other isn't sniffing it. Sounds like they need to be raised up a notch or 2 and I may have a bent prop on the starboard side. Am I on the right track?

[Moonlighter]

I do think you are on the right track, yes.

Especially if the motors are not showing any signs of cavitation or slipping ath their current heights, then lifting them at least 1 hole higher should help. Generally lifting one hole ta a time is recommended, and then test again.

When lifted, see what happens to the revs and the motors 'grip' on the water. If still looking low and grip is still good, can go up another hole. It really is a trial and error process.

Then, Once height is good, consider changing prop pitch.

The only other assumption is that both engines are running properly, and generally check out positively (eg compression etc).

Your target is both engines at least 5800rpm, trimmed out, at wide open throttle.

[redlowrey]

Mate it wasn't a rebuild, you put a set of rings on old pistons in a worn bore with a hone, I hope at least you put new big end bearings on the rods. The rings probably have not bed into the bores yet, and that will produce a bit more crank case pressure. for piece of mind why don't you give it a compression test just to see if they are up around two hundred psi.

[aquamort]

Mate it wasn't a rebuild, you put a set of rings on old pistons in a worn bore with a hone, I hope at least you put new big end bearings on the rods. The rings probably have not bed into the bores yet, and that will produce a bit more crank case pressure. for piece of mind why don't you give it a compression test just to see if they are up around two hundred psi.

Am i missing something here? How do we know he only replaced rings on old pistons? From his post he has put a new head on and replaced rings. How many hours on the block and pistons mate? Did you measure bore etc whilst apart?

As Redlowrey suggest maybe rings havent bed in yet? How many hours since rebuild and how did you run in new engine etc? Engine running fine otherwise? Does it feel/smell rich etc? The more info the better people can help

...ah ok i see the previous threads now, still doesnt answer all though.

[Lunchmoney]

Thanks guys. Moonlighter, I'm not having any cavitation or slip even in a hard turn so I'll be raising them a notch or 2 and see how they react.
Have about 35 hours on it since reassembly since it apparently doesn't qualify as a rebuild. I checked compression at about 8 hours and all came out between 185-190psi. New head, new rings, new thrust washer, new main bearings. Did not replace con rod bearings. Have a good shop near me that surfaced and honed my block whilst it was tore down. Mechanic measured by bores and said they were worn but not to the point I needed oversized rings or pistons. He recommended I replace all the rings with original size so that's what I did. Block and pistons have about 1100 hours on them. As far as break in after reassembly, I followed the new engine break in procedure as per the manual.
Again, the engine runs great, idles great. starts right up, no smoke or vibration. It's getting better fuel economy than the port engine. Runs like a top aside from not going beyond about 4900. At those revs, it is smooth as can be. No misses or sputtering.
I find it interesting that when the port engine is maxed out at about 5600 rpms, the starboard engine will creep on up to about 5100 from 4900. I'm no physics expert or mechanic, but that kind of tells me it's got something to do with drag more so than a mechanical issue. Maybe not. Thanks again all.