Misfire

Hey guy's, back again,,, And I want to thank all the people who have helped with everything so far, With the oil pressure and cooling issues taken care of we can actually drive the 442 clone with fresh 455 a good bit now but apon hard acceleration for a couple seconds, she takes a severe nose dive, put a fuel pressure gauge on and have 6 PSI normal drive that falls off to around 3 to 4 PSI on kicking it and is real slow to return back to 6 PSI, question) whats the small third hose for? a return? I want to clamp it off see what happens, just looking for thoughts or advice on feeding the small fuel bowl of Rochester Q-jet.

Olds64

Have you adjusted your carburetor at all? It sounds to me that your float level might not be set right. I your float is too low and the bowl runs empty on hard acceleration your fuel pump will have to work extra hard to feed the engine fuel.

If you have good fuel flow at idle your fuel pump should be fine. I've never heard of a fuel pump being "sort of" broken." They either work or they don't.

bccan

Some other things to check-

Check the rubber lines between gas tank & steel gas lines. Not unusual for the supply line to collapse after a few seconds of heavy draw by the fuel pump. Easy to replace & recheck.

Clogged pickup sock in tank?

oldcutlass

I'd also check the steel lines for corrosion and pin holes at the tank and along the frame. Check the hose to the fuel pump from the main line. The drop in fuel pressure is normal, what is important is flow.

Take the air cleaner off your carb, and look down the throat with the engine off. Operate the throttle linkage and ensure that you get 2 solid streams of fuel spraying when you move the linkage from idle to WOT.

Misfire

Not to sound like a Primadonna, but carb is all my handy work and is fine, I use to do road side rebuilds on Rochesters in high school, lol. Not had a chance to mess with it any today, its raining. But,,, what does the smaller third hose do that's on the pump?

455man

Third hose is a return line.

Misfire

Ahhh, any one ever pinched it off? see what happens? I'm not use to that on my Chevy's. And as far as the sock in the tank go's,,,, while installing the engine and hooking the fuel lines back to pump,,,that thing was self bleeding all over the place by it self, lol.

oldcutlass

You can block it off with no problems.

matt69olds

The 3rd hose is a return line. It bleeds off a small amount of fuel to keep the fuel pump cool (prevents vapor lock) and helps with hot restarts. With the return line capped the pressure with the engine off can go high enough to push the needle off the seat, flooding the engine. The return line style pump was used on cars equipped with A/C, they can get pretty warm under the hood.

Tedd Thompson

This is not my era car so if I'm sounding ignorant it is because I am but it sounds to me that you may have an unvented gas cap on a vented system. Just a thought....Tedd

MDchanic

Since running out of fuel under hard acceleration is a classic symptom of fuel pump failure, I'd recommend testing the fuel pump output as recommended in the Chassis Service Manual, and going from there.

- Eric

Misfire

Holy Shazbot, pinching off the small return nearly got me killed, stopped in parts store for things on another car, was there 10,15 min's, probly took 1.5 min's get on the road from parking lot, normal driving pulling out in traffic flat falls on its face, quick look at gauge....3PSI. feathering the hell out of throttle pressure slowly comes back and I move on.
while on way home, stop pick up pizza, in store same amount time, start car an just sit and watch gauge, with the line pinched it does hold residual pressure, but after few min's of just idle, pressure drops to 3 PSI and then climbs back up and is fine, never done that till pinching, WOW! there for reason? I'm gonna eat my pizza, then im going to reinstall return line, crank it for a min, shut off, unhook main fuel line and put it in catch can, start car an let it run till bowl is dry and see what I have.
All else, I do have a vac sec Holly 750 I can plop on, but trying to avoid it,

oldcutlass

I think you have a bad fuel pump? Capping off the line should not cause problems.

Misfire

OK, well,,,,Did what I said and car ran about a minute and pumped a good half gallon fuel before dyeing from fuel starvation, Guess this ones one me, lets go Rochester diving an find where float level is, more to come, hehe

Misfire

Well the float was off, I went ahead and dreameld out the needle seat some, ( while your there) and used a hand pump and made a float holder downer so I could visually see where fuel level was. find out tomorrow.

Misfire

well dadburnit, after all that, got little better, Carter pump time!