ok, 2 scenarios. first one i am using stock style valve covers, i have a k & n air filter/ flame arrestor on a 750 holley so there is no provisions for ventalation inputs on it. the valve covers are stock 502 automotive style valve covers which are exactly what the merc ones are except with grooves in them. so i have a hole on each side like th hp500 for example. what do i need to plumb these? i have a non marine carb with the vent tubes modified to marine so it has the vacume input that would normally be used for like power brakes on a car, can i plumb 2 hoses right into that? just 1? pcv valve?? breather?? i am confused! on my car engines one side has a breather and the other has the pcv valve routed into the carb. can i just throw a couple breathers on here and be done? most of the engines i see have tubes ran to both holes and both appear to have vacum pull on them....

second option, after market hardin style valve covers, no holes besides oil fill, do i need breathers? ventalation? i see allot use those tall breathers centered on the covers but how is that any different then 2 breahers on the stock style covers?

am i making this a bigger deal then it needs to be? this may be a dumb question but i am stumped and wanna wrap up this motor

K & N makes parts to run the hoses to the flame arrestor. Its a separate that you need to order. I used them on a K&N that I had on my Baja.
They are the Marine vent hose adapters. Here is a link http://store.knfilters.com/marine/boats.htm

so do i get 2 of those and run both up to it? i guess i am not understanding the idea of this setup, or do i need a breather on one side to actually get air flow going through the motor? thanks griff, be on the look out for a bright yellow and purple baha down at hayworth really soon, that will be my pain in the butt

I'm kind interestead in hearing about the breather on one valve cover question, also.

Right now I just have one side of the 509 plumbed up to a JAZ breather/can: http://www.jazproducts.com/breather_tanks.html

Figured it'd work just fine with only one side hooked up, but haven't ever bothered asking...

The adapters are for the filter. You just need some type of grommet and insert on you valve covers. You should be able to get those at any auto part store. Here is a pic of the set up on my Baja engine. Same set up on my 525SC also. These are basically stock merc set ups.

ok, i see that most boats have 2 hoses going to the flame arrestor, i guess i dont see how it is pulling anything out of the crankcase.... on the cars i run a breather on one side which allows air in and then the carb pulls air out... and then other boats i see that have breathers only on both sides instead... i am likely gonna run the 2 hoses to the flame arrestor, the k&n adapters are gonna cost about 40 bucks shipped whixh seems outragious to me since they are nothing more then some sheet metal but i gotta have them and my welder needs to go to the shop. i guess i am just confused on how the 2 common systems that i see (the 2 hose vs 2 breathers) are totally opposite of each other, why not one breather and 1 hose like a car?

The prices on them are nuts now. I think they were about $6 each when I got them.

and i have no issue with 6 bucks but 19.99..... dang i need to measure my grommets when i get home ans see what size the hose needs to be.

I was looking into this last year. Originally my crankcase vented out of the bilge with 2 long hoses running from the valve covers. I found a couple of articles that suggested the one breather and one hose for better crankcase cross ventilation. That's what I ended up doing. No complaints yet.
Yes, K&N charges way too much for those adapters.

so you did run it with one hose and a breather? i ended up with emi tall covers for center rise exhaust. no i have the no baffle issue..... i am still not sure what to do