Engine Cover / Closed Engine Compartment Air Starvation
I have a 21ft Bahner Jet boat with a BBC that I have been battling for a few years now. I rebuilt the engine over the winter and added a couple extra ponies where I can reliably. I took it out the first time without the engine cover just in case I needed to wrench on it and I could take a close eye on everything, it ran great. A couple of weeks later I changed the oil and put the engine cover and rear interior in and took it out and it was having really rough starts, rough idle, loading up etc. Took it home and couldn't find anything wrong with it, I would open the engine cover, turn on the battery, run the fuel pump a couple seconds and it would fire right up I couldn't take my and off the key fast enough. Took It out last weekend an had the same issues, thinking maybe ill turn the idle up and and see what happens. Opened the engine compartment, adjusted the idle, and it ran fine then closed the engine compartment ad it stumbles, open it and it smooths out, close it stumbles again, you get the point. I have the doghouse style engine compartment with the two seats on the side and a rearward facing upholstered air scoop on top and one of those small flame arrestors on the carb. I ended up taking the scoop off and it an great, ran even better with the flame arrestor off too but I didn't feel comfortable doing that with my kids in the boat. But now I have this big hole and a tiny flame arrestor sticking out the top that my kids love to stick their little hands down in. Has anyone else had issues like this? how do people get away with those air intake scoops without any problems? Could it be because my engine has a little more horsepower so its demanding more air than usual?
I have a CVX-20 jet with enclosed engine compartment- Never had any issues with air starvation. But I have Bilge vents and also, the area at the back of each side pocket is open to allow air in. It doesn't sound like you added a ton of power.....Do you have towels and stuff in your side pockets possibly blocking air flow?
There are a couple of other possibilities; Did you put A) a spacer under your carb, or B) a taller manifold? Moving the Carb higher might create interference between it and the engine cover- including the possibility that the engine cover is simply partially covering some of the Flame arrestor's surface area.....I have a 460 with approx' 400 hp (Cam/Weiand Stealth/Mild head porting/Really good quench) and am using a 5 3/4" diameter by 3" high stainless flame arrestor....After 12 years, I decided to have the carb rebuilt- but the spark plugs looked great.
My Bahner has a doghouse with a small rear facing scoop. I’ve got a pretty stock 454. Don’t run my blower much but I wonder if you added a blower on the compartment intake side air vent and fed your doghouse with fresh air, would it help at all?