I'll tell you how much a flame arrester makes..a couple of years ago ran a blower(177) and when first ran it would make 0 boost even though everything checked out...called weiand 1st thing he said run with out the flame arrester...did went right to 6 psi...and this was a H/P unit..ended up with a K&N only dropped the boost to 5.5...so they are not the same...somebody did a test of several here a while back...but just how the air flows down the carb will effect lean/rich. also watch out for not enough air into engine compartment...

Thanks for the info,
Iam going to pick up one of thoses 12in long 5in high oval flame arrestors and also cutting a hole in the engine hatch and fiberglassing a marine grade hood scoop. That should be plenty of air getting in there once the hood scoop is on I hope.
Erik

I'm mounting my scoops backwards this time around. keeps the long haired gals safe from being sucked into the blowers, less noise, no water intrusion from spray and will still do the job intended.

Intresting way of doing scoops. Email me the pics.
Erik

I'm not that far yet still have to build the hatch. K.C.

Who makes that 5" flame arrestor?? Very nice.

K&N makes some pretty big ones

gaffrig makes them !!!!! Also on a 509 you need to go bigger then 850 carb !!!! the 509 sucks atleast 1000 CFM air if run over 5500 RPM , mine did !

Did the HVH spacer help the h.p or hurt it, what was ur gains with the spacer. I have a 2" HVH spacer on my 502. just wondering if I should take it off or leave it. My motor has not been dynoed so I dont know if it helped or not.

The reason it leaned out is you created a vacuum at the bowl vents because of the restricted airflow. This causes less pressure differential between the fuel in the bowl and the venturi it is being pulled through, so flow of fuel slows down.