water mist coming up the back of the 300x cowling, see it in the video

[mrcrsr]

just saw the first video of my 21 skater running, you can clearly see mist/water climbing up the back of the cowling, i thought i was having an issue w/ plugs/tuning at hi speed(the motor would start to breakup after awhile at hi speed) but after seeing this the motor is getting wet, i'm dumping the tstat housing water and poppet dump behind the engine, so i need to reroute that, any other suggestions? http://www.youtube.com/watch?v=xKHd9Bct6sc

[Li'l Toy]

Charlie--There is at least one other thread on this issue--maybe on the green engine forum. Negative pressure by the shape of the hood, intake to the rear, the throttle position sensor gets wet and shuts down ignition. Dave Bush is now working with Simon, but doing the injected 3 litres; he has a hood modification that works but is accused of looking like a toaster. Another guy may have just come out with a hood that fixes the issue (he is working with Simon and the other guy), and a third guy has one with NACA ducts that seems to be controversial as to whether it works or not.

I looked briefly for the thread--it is either in the thread "300XS Upgrades" by Simon, or one that has maybe aged out by Bush called something like Best Outboard Ever Built.

[mrcrsr]

thanks pat, i remember something about that now, i think i'm gonna try introducing some air into the front of the cowling to see if it will keep positive pressure in the cowling

[native2]

Slow down a little and that won't happen.

[mrcrsr]

now what fun would that be cawley,lol!

[nate.]

get an e-tec, problem fixed. ;-)

seriously though, maybe some of yall can help me with this.... the 300 merc motors were pretty much designed to make small boats go fast right? now when those small boats go fast the motor sucks mist up into the hood doing bad things right? what is merc doing to address this design flaw? please forgive my ignorance and all but im just some overweight fla cracker with a fishing bote that will only do 60..........

[mrcrsr]

there was a post about someone w/ a merc under warranty trying to get the problem adressed, merc did nothing

[native2]

There was a guy who had a River Rocket w a 300xs. I remember he had a snout made that attached to the mid section where the water dumps out. It would divert the water out further down. Wonder if someone has a pic of it? It seemed to work. Hope I am making sense...

[BUZZIN' DOZEN]

http://www.youtube.com/watch?v=sV3ZoYscXVM

[nate.]

wow! what kinda speeds is this happening at? ill be buying a bayboat in the near future and the 300xs is on my "possible motor" list.

[Riverman]

This amazes me. Didn't Merc do any testing prior to offering the motor for sale?

[baddjonny]

How about a mini spoiler made out of plastic held on with double sided tape just as experiment , just use hotglue to hold it together that should break up the vacum that's pulling the spray up the back of the engine. you could also try a V wedge like the truckers use on top of the cab.

my 2
jon b

[Mike Nass]

We (HNR aka Haulin Nass Raceboats) have just release for sale through Dave Bush Racing only, two new drop on cowls that solve this problem and combined with Daves upgrades significant HP improvements. See link... http://www.screamandfly.com/showthre...NR-NEW-RELEASE

[Chaz]

The reason it's an X - XS problem is cuz there's nuttin else out that that run the speeds those mules produce ..
Packing the cowl with air would force feed the motor as well as keep "most" of the water from entering , but would do nothing to keep the water from being pulled up into the low pressure area behind the flat of the cowl and mid . Running the cowl backwards with the wide cross section facing forward and the trailing edge being narrower as well as shorter would help , but without coming to a point to bring both sides or the air stream back together evenly , all you would do is prolong the time (speed) where it would happen again .
As mentioned , the fix would be to "trip" some of the air into pressurizing the back side of the cowl to fool it into thinking that it was somewhat tear drop shaped .
On my rear engime dragster , I had a bit of a leak develop at the rear main seal , the only place that was wet was the deflector plate four feet ahead of the leak. The 18" open area between the driver box and engine would become a low pressure area from the air wizzing past , that it had enough power to suspend oil droplets for the trip against the grain . The fix was to add a couple of NACA ducts to pack some air in the offending area. ( that and fix the leak lol )
I think that there is some speed to be had in cleaning up the transom and cowling's trailing edge on these boats as speeds increase . I just hate the look of these "Euro" tails .. guess ya just cant have it both ways ..

[Instigator]

Charlie, the V-6 loopers do the same thing and I also have videos of it happening. The OEM air intake is at top/rear of cowling so the motor is ingesting partial exhaust w/air and water mist. On my hot rod motors I seal the rear opening and add vents to the front and or top of cowling. Doesn't stop it from happening but keeps it out of the p.head.
The cowling is forming a vacuum behind it at speed which sucks the air/water/exhaust up the back of the motor.