i just put together a stock 454, mercruiser, used a 350 hp cam, 049 heads, stock intake, qjet, thunderbolt 5, etc, w/ stainless marine exhaust, with the motor running i can see it pulling water back into the engine, if i take the riser off the inside of the manifold is wet, both sides- all parts pressure test good, if i use a piece of 3" hose and extend the dry side of the riser i see no water coming out( doesn't have a chance to mix w/ water), so i know it is not an internal leak in the engine or exhaust, compression and leakdown are good, i don't have any tight rocker arms-why is it doing this??? could it have something to do w/ the egr passage??? i mean, it roughly joins the 2 banks together, should i close off this passage??

nobody has any suggestions???

what are the specs on your cam, and what is your idle rpm?

You need a 14" drop from the top of the riser to the bottom of the tailpipe. That is what Mercury Racing calls for.

Gregg Reichman

What are the exact numbers on the cam????

this motor is stock, it has a mercruiser 350 hp cam

That cam shouldn't give you problems. Did you get a valve job? Leakiing exhaust valves make reversion worse. Too low idle speed will too. Try 800 rpm.

You have something going on. We sell that set for the 365 Magnum and the EFI motors. If your risers are very old, they might be the old style where the inner pipe doesn't extend beyond the outer pipe. If you would take a digital picture and forward it to '[email protected]', I'll try to help you.

i'll try to post some pics tonite, the inner pipe extends beyond the outer by roughly 2"

Is the engine/boat sitting at the same angle as it would be if its in the water??? If the bow is down, the lesser angle will allow water to revert.