1200 MAG meltdown... possible causes?

[ripcuda]

Howdy Gang,
I'm sad to say, the 1200 carby in my Rio had a catastrophic failure this evening. I melted down and holed the MAG piston.

The boat ran great last year. I winterized it with Stabil in the tank... fogging oil in the cylinder via carb throats until nearly stalled and a squirt in the plug holes too. All water (MAG water cover too) drained.

I've started it a couple times on the trailer this Spring without any fuss. Seemed to run good as I remembered... albeit smokey as it burned out the fogging oil. 3/4 tank of fresh fuel was added... yes... regular 87 octane.

Put it in the lake yesterday for the first time. Started fine, ran fine, no noticeable difference in power. Took the kids tubing... out on it for over an hour. With multiple shut-offs and restarts. Only thing I did notice was it took an extra second cranking to start when warm. I didn't remember that from last year. Big marine battery is still strong. Parked it for the night (at the dock).

My Bro-in-law took it out this evening to take his kids... and mine... tubing again. He's "checked out" on the boat... having used it a bunch in seasons past. He said it started fine and idled out fine. He then he put it on plane while pulling the tube for a number of minutes when all of a sudden it just lost power (no throttle change)... and came off plane. He throttled down and could tell it wasn't running right. Then shut it off. Upon restart attempt... it only would click... not turn over at all. They flagged down another boater and got a tow back to our dock.

This has happened many times to me... watching my watercraft get towed back... always seems to be when others are using them! Ah...

So my first thought was bilge pump might have stuck on and drained the battery or something battery related. Nope. Battery reads a strong resting voltage. And the engine will not turn over. I noticed right away the plugs looked weird... white-ish around their base. I pulled the closest plug (MAG) and doom... trouble.


I pulled the CEN and PTO plugs and they looked good... I dare say ideal. I used my tiny extendy flashlight and scoped out the piston washes. CEN and PTO looked great. Finger-nail sized clean spots at the ports. The MAG has a gapping hole in it. Bummer. I pulled the MAG head off...



So at this point... just looking for possible causes. Does this look like a lean burn? It is so powdery looking. Notice there are NO indent divot marks in the head. It's like it dissolved into powdery chunks. Not like the time this engine holed the CEN piston (I bought it that way). Could it be an overheat issue? My exhaust temp sensor/switch never triggered... sounds a buzzer in the Rio. I checked the oil lines and couldn't see any air bubbles in any of the oil lines... so I don't think it's an oil issue.

Thanks for the ideas and comments... and things to check.

[Mr. GP1800]

My guess is that the load on the engine pulling the tube combined with 87 octane fuel led to detonation. Have you ever checked the timing on this motor? Thats the first place i would look.

My guess is the motor was running in the 4000 to 5000 RPM range where the timing is still somewhat advanced. The load of pushing a bigger hull than a PWC and add in the load of the tube and BOOM. This is where i would be looking.

Of course i would check the carbs out as well.

[CrazyA]

My guess as well, would be the 87 octane with all the extra load. Did it have ethanol in it as well? Either way, low octane with extra load will take out the mag cylinder every time. Especially loading it in the mid range like Bryan said. Obviously as Brian said too, timing and carburetors should be thoroughly checked.

[ripcuda]

Good advice guys... thanks.

I honestly had not considered the extra load of tubing, bigger boat, slow speeds (mid-range)... and how that would affect the engine. But makes sense.

So this looks more like a detonation issue... verses a lean-burn issue?

I'm curious... is there a reason the MAG is the common victim of detonation related? Because it's runs the hottest?

Well... one good thing I guess... pulling the engine out of my Rio is pretty easy!

Cheers!

[K447]

...

So this looks more like a detonation issue... verses a lean-burn issue?

... is there a reason the MAG is the common victim of detonation related? Because it runs the hottest?
...

TXpro1200 has done some experimenting with altering the water flow balance through the red engines. I think he has also swapped ends on the water bar manifold and adjusted the flow restriction hole sizes, so the result is similar to the MSX 140.

After the changes I think he was happy with the more even cooling across all the cylinders.

See if you can find his posts on the subject

[CrazyA]

It seem to be fine all of last year, so I doubt anything is wrong with your timing. I just threw that out there because it never hurts to make sure everything is 100% spot on. One thing you could consider, if using this boat mostly for multi passengers and water toys and sports, is taking a little pitch out of the prop. I only say this if getting good gas is an issue for you on the water. An old trick for using watercraft primarily for water sports is to take a degree or two of timing out of it and a little bit of prop pitch out of it. I'm only suggesting this for people that are going to have heavy loads with 87 octane and cruising around in the 4 to 5000 RPM range as many do when towing water toys.

[ripcuda]

Good advice... thanks Crazy!
You described the normal operating use of my Rio. We don't need to go 50mph. We only tube and cruise around 20-30mph... so part throttle. And usually have multiple passengers (kids) and the tube to pull around... so extra load and drag for sure.

I can get better gas... just never thought it was needed since I wasn't racing or even WOT much at all. I'm used to worrying about detonation at full boost and high rpms. Didn't think mid-rpms on a non-turbo engine would be that demanding of octane. But as described... the timing advance being max at 3k rpms... in addition to the extra load... makes sense.

Thanks for the tips. I'll have to see which impeller # I have. Say I have the Virage TX (17-25 swirl)... would a Genesis (17-23 swirl) be a little less pitch? (I'm a little unclear on all the impeller #s).

I also need to check timing. I bought a used CDI when my original went out a few years ago. Retarding a degree or two of timing sounds like good insurance too for my usage.

Cheers!

[CrazyA]

In theory, yes, your impeller number examples are correct. The 17/23 would be LESS pitch. It will be interesting to see what impeller you have in there. I would assume that when they designed the boat that they took all of this into account. But who knows? A tiny bit of timing and a little less pitch won't absolutely kill your top end. Sure, you're going to lose some, but it sounds like you're not in it for all out speed. In all honesty, it sounds like you like to load the crap out of it with kids and cargo and pull water toys with a few more people on top of that. LOL. And there's nothing wrong with that. We just have to make sure you're safe. The gasoline of today is not what the gasoline of yesterday was/is… That's for sure. First lets see where you're at.

[HiPeRcO]

Put a Weber in it!

[ripcuda]

Put a Weber in it!

Haha! I gave it *very* serious consideration... swapping the heart of the MSX 150 and the Rio. But the Weber engine is too deep below the crank/driveshaft/jet-pump axis. It won't sit low enough to line up.

Shakey Big Red I guess it will stay.

Cheers!