There already is a check valve in every mechanical pump.
That primer bulb needs to go on the suction side of the pump. From pump to carb should be a one-piece all metal line. Cuz if you ever have a catastrophic failure at rpm, you fuel pump can flood the underhood with gasoline which usually ends badly. Yeah I know people say to not put a filter on the suction side. And if you put a generic 5/16 on on there I would agree. But those days are long gone! Just put a big ol' hi-capacity,metal-canister, EFI filter at the back, and yur golden. Mine was new in about 1999,lol, and is still filtering just fine.
My mechanical pump is rated 80gph, so in 8 seconds say, that would be ~23 ounces. But the 80gph rating is not specified at any particular rpm. You know that a can of coke is 10 ounces right, I mean just so you can get an idea of what 23 ounces looks like covering everything under your hood. the lightest gasoline molecules vaporize at about 95*F, so if it remains a liquid under your hood, that would be a miracle.
Jus saying.
IMO, a marine primer bulb under the hood is a really bad idea.
I solved my problem with a 750DP carb. Only after a week or so do I need to prime the carb, and I have a little squirt can I use for that, I mean the guy with the primer bulb has to open his hood just like me so ....... I just splash some gas down the primaries, jump in and floor it, then hit the start button, problem solved. And no risk of fire.
I spent several years in a marine shop, and have personal experience with primer bulbs, and I sure wouldn't install one under the hood of my hotrod. They are designed to lay in the back of the boat, for a few hours, every once in a while. When you get home, the first thing you do is unplug the fuel line, and put the tank in a cool safe place, away from the sun. I mean that is why the hose has a QD on it, for heaven's sake.
But under your hood, the engine is running close to 200*F and the headers idle at double that. And the fan is pumping hot air as hard as it can. When the engine gets to working, you can read the pipes with an IR gun and see 800/900/ and perhaps 1000 degrees on them. Do you really want a rubber primer bulb full of fuel, just inches away?
I sure don't.
I park my car in the carport I built on the NORTH side of my house, out of the sun. and , I ventilated my hood, so within a few minutes of shutdown, the engine is cooling off nicely.
But to be fair, daytime temps here in Manitoba seldomly exceed 37*C or about , lessee, that would be 99*F.
