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  1. #1

    Flame arrestor or air filter?

    Several of you guys being concerned about running my new setup, and questioning it on the fear of water intrusion, and or, a lack of filtering the air headed straight to the pistons has prompted this post.
    This is all just my opinion..
    Lets think about what a flame arrestor is actually doing on a jet ski to begin with.
    A long long time ago marine engines were the same as their landlubber cousins and had ignition systems comprised of mechanical components such as, points, condensers, distributors, rubbing blocks, etc. As these components moved, they wore and pitted slowly but surely and changed the timing dwell, which changed the timing itself, the point contacts pitted, distributor shafts wore and started to wobble, points actually bounced at hi rpms, so to counter that we put really strong springs on our points, which made them not bounce as soon but radically accellerated the pitting process.
    All this mechanical action and the wear involved in it created one problem that mandated the installation of the good old flame arrestor. The ever hated, backfire, cough, sneeze, misfire, are the more common names it had.
    In a marine engine, usually in a sealed area, this backfire could cause a hull, or engine compartment explosion from even a small amount of fuel/oil vapor if not extinguished before it blew back out from the intake manifold.
    So in essence, it is actually a fire extinguisher. Flame arrestor, flame stopper, flame extinguisher, all the same. That is its sole purpose in life.

    Enter electronic computer controlled ignition and fuel systems. Accuracy beyond belief, repeatability without wear at infinite rpms. When is the last time anyone heard a fuel injected, computer controlled ignition jet ski do the good ole backfire? I never have. Doesnt mean it couldnt happen though.
    Thats why are they still on there... Fear.. And liability lawyers i guess.
    Its real hard for a manufacturer to leave off such a saftey blanket after using it for so long.

    Flame arrestors and water intrusion.
    It seems there are many who think the flame arrestor will protect the engine in the event of water intrusion. It wont. Pour water on one and watch what happens. It goes right through it.
    Ok, so its also an air filter though.. Wrong again. I guess if you call something with the porosity of chicken wire an air filter you can. It will stop big rocks from falling into your engine, but it pretty much stops there.
    Most jet skis factory air inlet systems have a maze of plumbing that is simply designed to keep water out of the motor in the event of a complete roll over, it has zero filtering capability for either dirt, bugs, or water, or those pesky rocks.

    Water intrusion will only damage your engine if it takes a big gulp of water suddenly, or you decide to turn your ski into a submarine for extended periods.
    If you have minor amounts of water in the bottom of your hull, and are riding in chop, that water is being shaken around and atomized into the air your motor is eating for lunch, and you dont even realize it.

    Water can actually be beneficial in that form though.
    Anyone remember the water injection kits that simply used a windshield washer pump to squirt water in the intake manifold of race cars on WOT? Its purpose was to prevent detonation!
    How about driving your car when its super foggy out. Does the air filter stop water intrusion into the combustion chamber. Nope. Literally gallons and gallons of water are ran through your car engine and you dont even realize its happening. Even on really humid days it happens, on a lesser scale.
    So that means that on a jet ski, in here in florida, where the himidity reaches disgusting levels, as we ride, our engines are ingesting, you guesed it, gobs and gobs of atomized water.

    So my conclusion on the value of flame arrestors is based on these opinions.
    1- It is worthless as an air filter.
    2- It does nothing to stop water intrusion in my motor.
    3- It suffocates the engine as its trying so hard to pull in that incoming charge, and costs us that thing we love more than anything in this world---Horsepower and Torque!
    4 The chance of my ski backfiring and causing any kind of problem is equal to my chance at winning the lottery.
    Ill take that chance and throw mine in the trash,, or,, i mean sell em on ebay!!

    Another thought. Just as 2 stroke engines are super sensitive to any negative restrictions in the intake system, and a flame arrestor is a restriction, it also responds positively very quick to the enhancement of the incoming airflow. 3 weeks ago i saw a 70 rpm gain on a gp1300 by removing aftermarket flame arrestors only, and running bare naked throttle bodies.

    4 stroke motors have the force of a piston going down in a cylinder to suck in the incoming charge with authority, regardless of minor restrictions.
    2 stroke engines rely only on the vaccum created by the exiting exhaust gases to suck in the incoming charge, known as scavenging.

    Big difference in the two.. Learning the difference is the challenge..
    Once again, all just my opinion guys... Ross

  2. #2
    I would agree with that Ross. I have had a backfire through the throttle bodies before, but it was a quick flash and gone (not like its breathing fire for long periods). As for trapped fuel vapors, between the openings on the sides of the cowlings and many people have the windscreen modified and bucket removed. The vapors can not get concentrated enough to ignite anyway.

  3. #3
    All hail the Chief! fullboogie's Avatar
    Join Date
    Nov 2005
    I don't understand why on the one hand you say FA's are worthless as an air cleaner or to prevent water intrusion because they are as porous as "chicken wire", and on the other hand you say they are an inlet restriction. Hard to see how they can be both.

    I don't know what you've been running, but my R&D FA's have a cotton gauze lining that I believe does perform a function - keeping large debris and water out of the engine. And a backfire may be once in a blue moon, but I'd rather have the FA's in place in the event it happens. To each his own, though.

  4. #4
    I think the flame arrestors he's refering to are the thick metal basket flame arrestors sitting directly on top of the throttle bodies.

  5. #5
    flyboy's Avatar
    Join Date
    Nov 2005
    Destin, FL
    If you start telling the younger Forum members, to not run F/As and/or water jackets, you are about to have quite a few blown motors on this board.

    This MOD will Allow water intrusion more so than if you have a F/A installed.

    this is the same thing as saying cut 3 inch holes in the side of your ski for more air, but hope it don't sink. I't wont sink as long as you are on flat water, but who wants to worry about it?

    If nothing else, the F/A keeps water from "splashing" in the TBs.

    I will promote this MOD if some type of plate is put infront of the V-Stacks to keep water from directly entering the TBs


  6. #6
    My son (mohawk man) jeffsntx's Avatar
    Join Date
    Sep 2006
    Belton TX
    I think the board members here have enough common sense to determine if they need to be running F/A's or not. If your boat has a history of taking on any considerable amount of water the velosity stacks are probably not for you. If the hull stays dry, you arent going to hurt anything by getting rid of the F/A's.

  7. #7
    Happily Self-Employed WFO's Avatar
    Join Date
    Nov 2005
    Houston, Texas

  8. #8
    All hail the Chief! fullboogie's Avatar
    Join Date
    Nov 2005
    Considering all the places that are known to have the potential to leak (jetworks fittings, flush valve, exhaust coupler, cylinder head dumps, etc.), I wouldn't be comfortable running without *some* kind of protection over the induction. Not sure how much it helps, but I sure won't promote running without them. It isn't worth the .1 mph to me.

  9. #9
    (Hard to see how they can be both.) Thats always the problem when dealing with airflow, you cant see it.. Thats what makes it so weird..

    Back to my original post, i mentioned this is a race only mod, and hey, different srtokes for different folks, just throwing some debateable theory out there for everyone to chew on a while.

    Remember also, im testing on a fuel injected gp1300. You guys with carbs may not see anything if you try this. Carbs have boosters inside them which changes everything. The throttle bodied are a hollow straight shot through.
    Carbs and throttle bodies are very different in what they have to do...
    All my throttle bodies have to do is fill the motor with air. The carbs must also mix the potion properly.
    Only testing will tell the truth..
    Love seeing all the thinking going on...

  10. #10
    flyboy's Avatar
    Join Date
    Nov 2005
    Destin, FL
    Quote Originally Posted by jeffsntx View Post
    I think the board members here have enough common sense to determine if they need to be running F/A's or not.
    I agree 100% but when people talk about something new, sometimes the "need 4 speed" blinders only allow people to see the + and not the -.

    What WFO has looks to be like a good item to go with this MOD

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