Gas Explosion in Muffler

[RyanB]

We finally got our boat ready to fish, so I took the family down to the boat to clean her up and meet a carb guy to adjust the ratios on the Rochester's (they were running a bit rich after a recent rebuilds). I was starting up the stbd engine to warm her up and, mistakenly, gave it one too many pumps to prime the carb. When I hit the ignition on the 2nd or 3rd attempt to fire BANG! Like a big bang, that everyone around noticed.

Whether it was me priming once too many times or it was the carb being out of adjustment and was pumping too much gas, the end result was the same - my muffler is F'd.

I have the side exhaust, which I believe is the "under water exhaust" with the aqualift or vernalift mufflers, are these the same thing? (see pics below). My first question is how do these mufflers work? The one that I took out appeared to to be a two piece mounted at the bottom with a gasket wedged between the can and base plate. The port muffler appears older and looks like a one piece and also seems to be leaking, so I had planned on replacing.

After this incident I've read a bunch of threads on here and see some questions on whether or not this style muffler is a wise choice for gas motors. The design, if I understand it correctly, pushes water up and out which obviously created enough pressure that caused the damage when the motor backfired. The weak link appears to be the gasket, vs. just backfiring out the side of the boat. Is there a better option?

Lastly, any idea who makes these mufflers? I'm replacing both at once, to just get it done. I'd like to get them ASAP to get on the water. Is Sams the best place to try?

This whole thing really put a damper on our excitement to finally get out on the lake, after months of work (wife is less than pleased). But, it could have been worse. Kids weren't on the boat and my wife was in the front state room should anything gone worse. At the end of the day, I suppose any problem that can be fixed with $$ isn't that big of a problem.

Any advice is greatly appreciated!

STBD Muffler:

STBD Muffler Blown Gasket:

Port Muffler: Different Bottom mount and looks like leaking

 

[rustybucket]

What boat is this in? year/model? What models are the engines? Pics of the exhaust flow setup might be helpful.

 

[RyanB]

What boat is this in? year/model? What models are the engines? Pics of the exhaust flow setup might be helpful.

That would have been helpful. Its an '86 36' Sedan. '86 Crusder 454 (350hp). Here is the best picture I have of the exhaust flow, I can try to get a better picture later this week.

 

[MadHatter53]

I have these for a pair of 454’s if you think you can use let me know. They do need to be mounted horizontally. From what I see in your pics I can’t see anything real bad. Maybe it backfired thru the carb?

 

[RyanB]

View attachment 50056I have these for a pair of 454’s if you think you can use let me know. They do need to be mounted horizontally. From what I see in your pics I can’t see anything real bad. Maybe it backfired thru the carb?

Thanks but I’m not sure I have the length to accommodate those. The damage is in the bottom of the muffler, it blew out a gasket or plate. You can actually see where the screws pulled out of the plywood when it happened,So no being loose when I turn over the motors water will pour into the bilge, out of the bottom of the muffler. Everywhere I look online, I thing looks close to the mufflers I have. I’ve called and texted Sam’s too but can’t get a reply/answer.

 

[BOATER BOB]

Its a vernalift muffler Centek makes them .

 

[Captain Ralph]

Contact Centek and give them all the data on your boat you can. They more than likely made the original muffler.

https://www.centekmarine.com/contact/

Find another mechanic. This one risked your lives and near lost your boat for you.
Probably has no idea how to work on marine fuel systems.
He's not working on Papa's old Chevrolet.

There is a reason for MARINE carburetors. There is a reason for MARINE fuel technicians. There is a reason for factory MARINE specifications on marine gas engines.

Lives depend on these reasons.

 

[RyanB]

Contact Centek and give them all the data on your boat you can. They more than likely made the original muffler.

https://www.centekmarine.com/contact/

Find another mechanic. This one risked your lives and near lost your boat for you.
Probably has no idea how to work on marine fuel systems.
He's not working on Papa's old Chevrolet.

There is a reason for MARINE carburetors. There is a reason for MARINE fuel technicians. There is a reason for factory MARINE specifications on marine gas engines.

Lives depend on these reasons.

So far Centek is the only place that can make them from scratch. The problem is that their lead time is 2 1/2 months, with a ship date somewhere in August. Being that I'm in NY this was very bad news. They aren't cheap either, but at this point it really doesn't matter, I'd like to leave the slip!

In the mechanics defense, he didn't even touch the carbs when this happened. He was just a friend of a friend that was down adjusting the mixture screws on another boat. Being that I was running rich, little smoke out the exhaust, I wanted him to take a look at mine to dial them in. The back fire occurred when I was cranking the stbd motor, just to get it warmed up and to temp.

Two separate mechanics have told me that there should be no way for that amount fuel to be engine to back fire that bad. The only person to touch the carbs so far has been myself to increase the idle slightly, as the stbd motor was so low it would stall out at dead idle.

I'm going to yank the muffler tomorrow to see if the bottom can be repaired, perhaps there was a blockage of sorts in there and the pressure caused the damage? Will know more soon!

 

[Captain Ralph]

(they were running a bit rich after a recent rebuilds).

Running rich or leaking or flooding.
Q-Jets are notorious leakers. Worse when automotive attitudes are involved.
Un-ignited fuel passed thru a cylinder or two and was ignited in the exhaust manifold, from one of a few sources..
With the same energy it makes to drive a piston down, the expanding explosion blew out your water flooded muffler, possibly with more fuel & fumes in it's voids, continued to expand like a hand grenade.
I have witnessed lots more damage than this.

Sorry if I appear to be bashing you, I get real excited about gas boat issues.
The best of all of this, everybody is safe and O K,

Some times it does not turn out that way.

 

[RyanB]

Running rich or leaking or flooding.
Q-Jets are notorious leakers. Worse when automotive attitudes are involved.
Un-ignited fuel passed thru a cylinder or two and was ignited in the exhaust manifold, from one of a few sources..
With the same energy it makes to drive a piston down, the expanding explosion blew out your water flooded muffler, possibly with more fuel & fumes in it's voids, continued to expand like a hand grenade.
I have witnessed lots more damage than this.

Sorry if I appear to be bashing you, I get real excited about gas boat issues.
The best of all of this, everybody is safe and O K,

Some times it does not turn out that way.

I'll take the bashing, honestly it scared the hell out of me hear that. This was one of my main reasons for wanting diesels. The only think that I can think of is that I had the idle up too high and held the throttle cable open and it flooded?

I've had several different carb guys tell me that the amount of gas it take to pop a muffler that far downline, is very unlikely. Still, I'm a bit hesitant to push the start button again....

 

[Captain Ralph]

I'll take the bashing, honestly it scared the hell out of me hear that. This was one of my main reasons for wanting diesels. The only think that I can think of is that I had the idle up too high and held the throttle cable open and it flooded?

I've had several different carb guys tell me that the amount of gas it take to pop a muffler that far downline, is very unlikely. Still, I'm a bit hesitant to push the start button again....

It takes very little gas, It is the fumes that could started a flash rite at the exhaust manifold, and like a flash going down a gun barrel, your flash traveled until it hit something hard; non-compressible pool of water in the muffler bottom.
IMO; Your carb guys don't know much about marine systems and what little it takes to cause such damage.

Just had an idea, an example maybe; race cars engines, that pour the gas in, with straight exhaust popping and flashing.

You may have experienced just one of those exhaust pops.
Just one....