4500 RPM... something's wrong

[Tweek]

I put new 373 rear in my 80 over the winter, now when I go WOT somewhere in the 4500 rpm range the car falls flat on its face, like its running out of fuel. I replaced the distributor, coil and module, after the problem started, and no resonse, the same thing. The motor has about 7000 miles on since a rebuild, so I pulled the valve covers and checked to see if maybe I had valve float, or to much lash, and all where fine. Now I need to check the fuel system, and I don't know where to start. I was going to pull the line at the fuel pump and blow compressed air into the line back to the fuel tank to free any deposits that may clog the line, and check the fuel filter....anything else? My carb is a stock Q-jet that has always ran perfect, not sure on the fuel pump, it was on the car when I bought it. Someone told me today that it sounded like a float level problem, and that Q-jets where known for not being able to provide enough fuel under heavy acceleration...Sound right?

Hope someone has some better ideas than what I'm coming up with, I'm getting fustrated!


Ron

 

[mike weyman]

it sounds like fuel to me also,maybe plugged filter, weak pump,collapsed line.if it ran before the swap, it should run now.it's not crossfire injection??or a 305 is it??both tend to run out of air too soon.i really think it is not related to the swap.mike

 

[George Black]

I agree with Mike: (1) filter (2) pump or (3) fuel line. Check those then go from there.--G.P.Black

 

[Jack]

Sounds like a fuel problem ... but OE & OE-type replacement modules tend to go limp about 4500. Hot rod modules good thru higher revs.
JACK:gap

 

[Chuck-75]

I have a 75 and I pulled the smog pump and installed new sidepipes, Im having the same problem. step on the gas and around 3/4 of the way throught acceleration (around 4500rpm) my car just stalls.I also thought about the fuel?, but Ive been told that I need to adjust the Vacum secondary upper butterfly ,so that it opens a little sooner.(i also have a quadrajet on my stock l-48,400 auto.)my car ran just fine before I made the changes.ask around and post what you here about the secondary butterfly therory?,,,,,,,,,, to adjust you need a mirror and look under the passenger side of the rod that holds the upper butterfly in place,theres an allen screw that needs to be losened and then with a small standard screwdriver turn the set screw .. (i was told 4 times how to do it.I still had trouble so I finally took the car in and after they showed me where these screws were I finally figuredout what they were telling me) but I still havent worked on this problem just yet, other projects were in the works.... if the filters dont solve yr problem then this might be the next place to consider?,
just my $.02 save the wave.

 

[mike weyman]

tweek, it could be possible the catalatyc convertor is partially plugged and won't let full exhaust flow.just a thought, ive had this happen myself on another vehicle.mike

 

[Tweek]

Thanks for all the ideas guys, it turned out to be a fuel pump! I changed it out thursday, and in 2 days I have run a tank of gas out of it. I think its drinking the stuff now, the old pump must have been going bad for a long time. But anyhow, it runs great again!

 

[George Black]

Thanks for the report back identifying the source of the problem (fuel pump). That is one of the great values of this forum--we all benefit!--George B.

 

[norvalwilhelm]

If you suspect a fuel feed problem and the motor always falls flat on it's face at 4500 why not run it slowly up to about 4000 then punch it. You will have enough fuel in the floats to carry you past this 4500 limit if it is just a fuel feed problem.
I had the same problem with a holley 850 and it turned out the floats were collapsed. My motor fell flat on it's face every time but by bringing up the rpm slowly close to the rpm limit then stomping it I found it would leap past the old problem spot and just fall flat at some higher rpm.