My car stumbles and noses under load. Mainly when I put my foot into it, seemingly when I would anticipate the secondaries opening up. I have had the same hesitation problem since I bought the car. I went from an edelbrock 750 to a rochester qj and the problem remained. This kind of leads me back to fuel pressure issues. I replaced the fuel pump some time ago but installed it the same as the other. I capped off the fuel return line. Could it be that my carb is flooding itself out because of this? Would I be putting myself & car at risk to temporarily mount a recovery bottle under the hood to test whether of not this may be the solution? I recently had a HEI dist build and curved. I do not think I have ignition problems.
Check the fuel tank vents and the fuel tank pick up. I assume you checked the filter in the neck of the Q jet.
The tank is not vented but I do have a vented cap. I have run with it off and that made no difference. Fuel filter is new, carb is new, dist is new, fuel pump is new, sending unit is new, plugs are also new. I have new ignition wires headed to me from Summit. I'm wondering iif my fuel pressure gets too high because I do not have a fuel return line?
You say the carb is new. Is it a remanufactured carb? Q-jet? If so, have you tried adjusting the secondary air valve opening tension?
Q-jet 800 cfm it was rebuilt and offered up here by another member. Been through all of the adjustments. Timing, advance, vacuum ect. Is the fuel recovery line nessesary?
If it is a fuel pressure problem, you need to test for that. Rig up a gauge that you can tape to the windshield, and then go drive it. 4-6 psi is what you want at all times. Do that and we will go from there. Otherwise, this thread will go on and on and we won't get anywhere.
I do not know if it's a fuel pressure issue or not at this point. I'm not trying to draw this out. Just looking for suggestions. trust me I'm more interested in performance than I am this thread. My main question pertains to a fuel recovery line which nobody has yet shared an opinion on. I like your thinking on the FPG. I'm on it.
OK, not to be a jerk, but you haven't even told us what your're working on. How can you expect to get good help if you haven't told us year, make, model, engine, perf mods, etc.? The more info you can give us, the better the answers will be. Bosch spark plugs are the worst spark plugs ever. Period. I'd HIGHLY recommend replacing them with the correct A/C plugs for your application, even if they aren't causing your problem. And if you are talking about a typical Stage 1 style fuel pump, using the search feature you would find that blocking off the return line has only a very minimal effect on fuel pressure ( maybe 1/2 PSI). It was more of a "feel good" modification. If you feel that your problem is too much fuel, it would smell pig rich and foul plugs. Have you inspected the plugs lately and what were your compression readings?
Nobody is a jerk for trying to help me. I'm just trying to figure things out in an open discussion. I will try to limit my discussion by providing more details. the engine is a 1973 455 with stock heads, QJ 800 carb and a RV cam.
I don't run the return lines on my Buicks. Like Jim first recommended, double check all the rubber lines in your fuel lines from rear to front. If the rubber areas are cracked, it could be sucking air in and that would be a problem. Also mentioned, was the tightening of the secondary flaps. My guess is, a quarter turn tighter and you will see an improvement.
See that's exactly what it sounds like to me. The fuel pressure test will go a long way to narrowing down the cause. If this happened with 2 different carburetors, it stands to reason that the problem lies outside the carburetor. Blocking off the return line will not cause you any problems other than possibly increasing the likely hood of vapor lock.
I'll go gack out and evaluate it based on you suggestion. I appreciate your input. I'll have to research the vapor lock thing. I'll have to take a close look at my lines too. Thanks for the help. Lastly I apologize if my comments were abrasive to anyone. I do appreciate every ones contribution. This website has been a blessing to me.
Seems to me that if you have thr right fuel pressure at idle that there should be enough fuel in that bowl till give you a shot when you stomp on it and then it should die with lack of fuel pressure. If the fuel pump couldn't supply I would think you would notice this when you need gas under load while moving. If you punch it from stop and it immediatly dies I think you are looking at something else. Just my opinion.
Is there any chance that your problem could be caused by a vacuum leak somewhere, such as carb/manifold gasket or a vacuum line? Do your spark plugs show signs of lean or rich fuel mixture? Does the engine idle normally?
No updates yet. I'm waiting for my new wires to arrive from Summit. I'm going to throw them on and then put it on a wideband.
