Engine Issues

[Rusten]

Doing everything I could to restore my Moomba after an overheat/engine replacement (it only had 90 hours usage prior to this), I took a long breather -- and just returned to the task. I have two interesting observations and I wondered if any Moomba owners can chime in on their experiences or whether any of this is normal:

(1) The Indmar/GM 350 carburated utilizes a Holley 4bbl. Since replacing the engine, I haven't been able to get past 4,000 RPM (approx). Someone suggested the carb's secondaries might not be opening. This week, I tested the boat, keeping an eye on the secondary valves. They didn't appear to open, at least not more than possible 1/10th of a turn (if at all).

TO MOOMBA OWNERS: If you watch your secondaries on the Holley 4bbl -- at what RPM range should I notice them start to open, generally. Keep in mind these are vacuum driven and the boat needs to be in the water (under load) rather than being run with a flush-kit. Otherwise the 350 engine will rev easily to 5,500/redline without opening them. But under load, should these start opening before 4,000 RPM?

(2) I purchased a new HEI ignition module from SkiDIM that matches the original. This module is supposed to have the advance-curve on-chip, just like the original module from Indmar. First task after installing the new module, I set the BASE timing in "freeze mode" (the advance is turned off by providing positive to the shunt wire). To verify, I increase RPM's in freezed-mode and the advance remains locked. With base timing set, I return to "norma" mode and the advance now reads 20 degrees faster than where it was set.

In other words, I set advance at 10 BTDC in "freeze mode" and I wind up with 30 BTDC after the module comes out of the freeze. This makes perfect sense since the module actually provides 20 degrees of retard, in order to emulate 20 degrees of advance (e.g. an electronic module can't actually provide "advance" so instead it starts out advanced, and merely retards less as RPM's increase, effectively providing an advance curve).

The funny thing is... Although the module clearly has 20 degrees of retard (because immediately out of "fixed mode" there is 20 degrees additional advance), the module does *not* provide more than 10 degrees of advance at 5,000 RPM (actually all 10 degrees are provided at 3,000 RPM and it doesn't get any higher).

The reason I replaced my original INDMAR module is that it too only gave me <10 degrees added advance up to 3,000 RPM and nothing more. I don't know what it did before, but since I replaced my engine (short block only), I tested it and realized it didn't meet the specs provided by Brian Raymond. I thought this might be the source for my performance problem.

I once read a post by Brian Raymond that explained the INDMAR ignition module should provide 20 degrees more advance over 4,500 RPM (if memory serves), providing a 10 BTDC that reaches 30 BTDC upon WOT. This makes sense as GM specifis this engine to run at roughly 10-to-30 curve.

MOOMBA OWNERS: Have any of you noted that your advance is only 10 degrees maxing out at 3k RPM? Am I just crazy?!

Thank you in advance for any information,
Rusten

[smokedog2]

You know more than I do, but in an effort to delay my 2000 m swim here ya go.

There are books on this stuff, big, big books that cost a few $100 (last I heard), they target a motor. The boat mods may be in another book. Your dealer MIGHT have them, but they will be for the motor that came with the boat. They may be on CD now. These books have updates. I know you have the book if you are doing this but you might not have the updates. Are they on CD now?

If you are replacing a motor, why not go to fuel injection, esp if you are doing the work? Carbs are not simpler than FI and always fussy. I’ve never liked them ever since a leaking Carb lit my Plymouth Duster on fire 20 years ago.

Someone here will know more about the RPMs settings etc IF the motor is one they use on the boats. If it is one used by Sanger etc. I’d check there. I know I run WOT at about 4000 RPM (EFI Engine) and that they have crept up as the boat hours have gone up.

Why/how did the engine overheat in the first place? 90 hours is not expected status.


SD2


One other thought. If the Carb is definitely the problem IF there is a problem why not just press on. You can fuss all you want with the carb after you get the boat running. If you are using the original carb, changing the thing may be just adding to your work later.

Be sure it does not leak.

[Rusten]

Thank you for the reply, Smokedog. I'm a bit confused by some of the content in your post and I'm hoping mainly to find answers to the two main questions, based on other people's experience here. I am running the standard INDMAR 350 Carb engine that is default with the non-V-drive Moombas (Outback & older models).

One update. I explained the advance numbers incorrectly. When I set the advance in 'freeze mode" at 10 BTDC, this changes immediately to 21 upon "un-freezing" which yields up to 30 total advance at 3,000 RPM (and never goes any higher). In other words this would cause my engine to idle in 21 degree advance, which I feel is much too high. Could SkiDIM be wrong -- is this not the matching module used by INDMAR?

Thanks again for any suggestions,
-Rusten

[Buttafewcoe]

I'm a bit confused by some of the content in your post

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sd.....he has that effect on ppl. But still provides excellent insight
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Truth be known, me?......not so much
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lmao
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My '04 Outback DD revs to factory specs. so I am not sure of the issue. I think I've read somewhere that the V-drives are pinched off simply because of the V-drive configuation. More complicated drive train = more fragile components? It could be the trans, with bevel / angle gearing cannot stand the rpm's that a DD can.......4200 on a V vs. 4600 on a DD.
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Hope this helps
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B

[zabooda]

My 98 Mobius, 350, the 4bbl seems to kick around 3200 rpm. I can tell they're kicked in by pulling back from full throttle and you can hear the 4bbl closing up. It sounds like the hiss from an air hose for a second.

[Buttafewcoe]

And it may simply be a linkage problem. Check to see how far you have to engage the throttle lever before linkage @ the carb starts to move. If lever moves a quarter travel or more b4 linkage do, take out some of the play and test again.
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Hope this helps
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B

[Rusten]

Thank you Buttafewcoe & zabooda.

I have the straight shaft. I believe it previously maxed at 5,200 RPM before the new engine; now I'm maxed out at about 3,900 - 4,100. Buttafewcoe, you mentioned that yours revs to spec; I didn't see a spec for max RPM's in my literature -- can you tell me where that is?

The first thing I checked is the linkage, although maybe I'm not doing it right. I had removed the throttle cable and instead used my hand to push the carb-throttle all the way down, making sure it is absolutely maxed -- same result.

It revs easily to redline *without* load. Is there something that could be putting too much load on the motor? I checked the alignment of the shaft and the prop is perfect.

Anyone have a Indmar 350 Carburated (310hp) in a similar boat (Outback, Kanga)? Do you happen to know what your WOT RPM's are?

Thank you in advance,
Rusten

[Buttafewcoe]

According to the book, 4800 RPMs. At WOT 4800, 46 mph. But that is for my '04 Outback.
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Hope this helps
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B

[Rusten]

That does help -- and confirm my original experiences, thank you.

Assuming the engine works fine (which isn't entirely true, but assuming for now). Is there any reason why I could have exessive load on the engine. For example, is there something that could be incorrectly linked to the transmission to make it more difficult to turn the prop?

I've checked the prop and it's fine -- I'm just wondering about other issues that could create excessive load, that would in-turn would limit the engine's ability to perform.

Thanks again!

[Buttafewcoe]

A freshly rebuilt engine that has been put together 'tight' (minimum clearance on the journals, et. al.) may not rev to capablilty as a broken in one would.
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You may want to try a 10w-30 or 5w-30 oil during the break in. Think carefully about that before you do.
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Does the prop turn by hand? Or is it a struggle to get it to move?
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Engine to shaft alignment?
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Do you have the stock prop or an aftermarket one? All things being equal, to get more revs (and maybe loose some top end) you could reduce the pitch of the prop (aren't these 13 x 13?) to gain rpms, don't know if that's the answer, tho
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Hope this helps.
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B