Flame Arrestor for Outboards?

[Chrisravosa36]

I realize that inboards are required to have one, but not outboards. Im wondering if this is something I should worry about? Also with this motors, if there was a backfire, would it be best to have a pressure tank? Id think because there is no oxygen in the pressurized tank the fumes cannot ignite? Would a flam arrestor help this? The reason I ask is because there is some light scoring on the cylinders, not deep but can you barley feel it with a fingernail.

 

[interalian]

Inboards use flame arrestors to prevent bilge explosions. Not a problem on an outboard. And a pressurized tank will still be full of oxygen...

 

[jimmbo]

What would light scoring have to do with a flame arrestor?

 

[sutor623]

You sound paranoid Chris. More paranoid than me!!!

Make sure all your safety gear is in check, make sure you arent leaking fuel under the hood, and that all your electrical connections are clean and coated with liquid tape and let 'er fly!!

 

[F_R]

Outboards do not have flame arrestors on the carburetor because they cannot backfire through the carburetor. They cannot because the reed valves prevent backflow. OK, somebody will point this out anyway, so I will now. Outboards didn't have reeds till around 1950's. Prior to that they often had rotary valves, and yes they did backfire through the carburetor, and yes they sometimes caught fire.

Your thoughts about pressure tanks are not reasonable. They are pressurized with air and fuel vapors--very explosive. But because they are sealed, there is no way for an ignition source to get in them to set them off, so no danger. Contrary to what some people write, they do not blow up. If ANY tank leaks, it is a fire hazard though.

 

[Don Hansen]

Four stroke outboards don't have reeds, do they?

 

[flyingscott]

Four stroke outboards don't have reeds, do they?

Inboards and inboard outboards are in an enclosure in the boat much higher chance of an explosion and fire. An outboard is more open and has a much lower chance of fire/explosion. That is why you have spark arresters and blowers on I/O and inboards, If you don't believe that, the insurance is actually higher on I/Os and inboards. The airbox on outboards is more for quieting the intake noise than for spark arresting. When I say inboards I include jets. Since fuel vapor is heavier than air when it gets loose in an outboard it falls out the bottom of the motor into the atmosphere. If fuel vapor gets loose in an I/O or inboard it falls to the bottom of the boat and stays there as a fire hazard. That is why spark arrestors on those and not on outboards.


Are you worried about this, because you are worried about blow by combustion getting into the fuel line because of the scoring. Tell you right now that will never happen.

 

[Chrisravosa36]

Are you worried about this, because you are worried about blow by combustion getting into the fuel line because of the scoring. Tell you right now that will never happen.

Yup. Thats what I thought.... my motors a 69' so will a presurized tank work the same as a non?

 

[Chinewalker]

Your motor doesn't use, and can't use, a pressurized tank... Go ahead and run it as it was designed. And if the blow-by bothers you, tear it down and fix it.

 

[flyingscott]

Stay with the regular tank and don't worry about it. A pressure tank is a waste of time and money for your motor

 

[F_R]

Four stroke outboards don't have reeds, do they?

I didn't think the OP was talking about 4-strokes. But no they don't have reeds. As far as I know they don't have open carburetors either.

 

[StarTed]

combustible gasses have a lower explosive level and a upper explosive level. That means that under a certain ratio of gas and air there is no explosion and above a certain ratio of gas and air there is no explosion. The only way a tank can explode is if it is empty or near empty. On top of that the flame front would have to get through the fuel line to the tank. Can't happen, not enough air in the line (the ratio would be above the upper explosive level).

 

[nabiul]

Tanks and fuel trains have filters, sometimes these are fine mesh screens. You can call these flame arrestors if that makes you feel better.

Also on the hazards of using pressurized tanks.

http://outboard-boat-motor-repair.com/Johnson/Pressureized Fuel Tanks.htm

 

[F_R]

That article on pressure tanks is well known, and while I highly respect the writer, I dispute the idea that they blow up. If they are weakened by rust-out, yes they can rupture under pressure. But so can the non-pressurized tanks if they are likewise rusted. Non-pressurized tanks have a one-way vent valve and can build pressure when sitting in the hot sun. The one-way valve is required under law in order to prevent fuel vapors entering the environment.

I also respect Star Ted's comment on combustible mixtures. He is right on everything he said. Except for one minor detail. The motors that have pressurized tanks pressurize them by pumping air/fuel mix from the crankcase into the tank. That is the same fuel mix that is going to the cylinders and it is a combustible ratio. If it were not combustible ratio, it wouldn't run.

Long story short, these tanks just do not explode because there is no way for an ignition source to get inside them.

 

[fhhuber]

And...

If you've ever been running a vented system and forgotten to open the cap vent, you know what happens. You can run for a while then the engine starves. Wait 5 minutes and you can run again for a while. (repeat until you figure out you need to open the vent)
This is your most likely result from trying the incorrectly installed pressurized tank with a non-pressurized type (mechanically pumped fuel) engine
No crank pressure line... no air getting in the tank...

Not many have run into the pressurized tank boosting a fuel pump. It gives excess pressure in the fuel lines which may or may not overcome the carb float trying to keep the carb from flooding. Might be fine... might flood out in under 30 seconds.

 

[Chrisravosa36]

And...

If you've ever been running a vented system and forgotten to open the cap vent, you know what happens. You can run for a while then the engine starves. Wait 5 minutes and you can run again for a while. (repeat until you figure out you need to open the vent)
This is your most likely result from trying the incorrectly installed pressurized tank with a non-pressurized type (mechanically pumped fuel) engine
No crank pressure line... no air getting in the tank...

Not many have run into the pressurized tank boosting a fuel pump. It gives excess pressure in the fuel lines which may or may not overcome the carb float trying to keep the carb from flooding. Might be fine... might flood out in under 30 seconds.

When I first ran the motor, i DID use a presureized tank, and it worked great. But I will try the metal one out first to see if there is a diffrense.

 

[jimmbo]

When I first ran the motor, i DID use a presureized tank, and it worked great. But I will try the metal one out first to see if there is a diffrense.

How did you manage to hook up a pressurized tank to your engine? As for trying out 'the metal one' what was the pressurized tank made of?

 

[jimmbo]

Tanks and fuel trains have filters, sometimes these are fine mesh screens. You can call these flame arrestors if that makes you feel better.

Also on the hazards of using pressurized tanks.

http://outboard-boat-motor-repair.co...el%20Tanks.htm

That article has several errors

" It is difficult to get these tanks to seal properly, even when new. If the tanks leaks, gas and oil will escape into your boat and into the air."

The tanks do seal very well

"If you are out on the water and your tank fails to hold pressure, the only way to run your motor is to hold the tank up above the level of the tank and let fuel gravity feed to the motor."

You can use the primer button to supply fuel to the carb

"These tanks were not simple to operate. You have to pressurize the tank with a hand pump before you can start your motor. You also have to depressurize the tank before taking the cap off."

Pushing the primer button does not pressurize the tank, it just pushes some fuel to the carbs. It will work with the cap off the tank. The cap has to be unscrewed several turns and it will depressurize as you unscrew it. I guess if you can remove the cap in less than 2 seconds it might pop off​

 

[Chrisravosa36]

How did you manage to hook up a pressurized tank to your engine? As for trying out 'the metal one' what was the pressurized tank made of?

I just hooked it up to the motor. IT clipped on. It was plastic

 

[ondarvr]

I think you may be confused on the style of tank you used, let's see some pics.