New fuel pump, causing Flooding

Iowa409

Well Known Member
Supporting Member 3
I know its easy to get way deep on the simplest of problems, and quickly over think things, I do it everyday.

I would never have changed a thing, it ran great, and it was one of the best sounding engines I have ever heard, that's how well it was running.
But the hairline crack, blew open to point it was dumping raw fuel all over the headers and ground, it had to go bye bye.

Now we all know its a small HSP 409, but, a good running. tuned engine sounds good, I have been up this side of the problem and down the other, and I am willing to bet all the money in Dons, wallet, that this fuel pump is going to fix the issue, right back to where it was running before.

But through the forum, I have learned how to go from a-z testing the entire fuel system, I feel comfortable enough to say, after testing these with the pressure gauge/PSI...........there is nothing, that is STANDARD, rated at 6.0 PSI, does not mean that's what its delivering, I never tested the original, I bought one that was supposed to fit, yada, yada yada. BUT I did test the last 2, both rated the same, both the very same part number/manufacture

The first one reading in the 20+ PSI, flooding carb, that was JUST running perfect, 10 minutes before (The leak/crack in the original was very sudden)
Changed to this one immediately.

Work through troubleshooting with Don and other members, take tests, go buy 2nd Fuel pump, a exact warranty replacement
This reads right at 6.0 PSI on start up and idle, you open the throttle up and you can watch the inline clear fuel filter go dry, and the fun ensues
just before it dies, pressure steadily drops under 3 PSI, under load. Now I don't own a dyno machine that can print out a graph or scale to read
But i do have a pretty darn good idea when I am out of fuel.

Now if I am wrong I will say, when it comes Wednesday. But I think with all I learned here, its been tested out and proven, of course its not on and running yet.
 

boxerdog

Well Known Member
Supporting Member 5
Until I watched that video, I had no idea a fuel pump could run normally under load, then lean out to a dangerous condition at mid-rpm like that. Pressure is important, but gph seems to predict a more stable fuel curve when engine demand goes up. And 5/16" line can also become a problem in many cases.
 

Iowa409

Well Known Member
Supporting Member 3
Quick update:
The new Edelbrock 1721 fuel pump (6 PSI) works perfect, great idle, great flow under load, just goes to show me, not all fuel pumps are created equal, EVEN the same fuel pump with the same part number, there is a real issue with quality control that has been proven out in this situation.

I wont rehash it but you seen in my previous comments, all over the place with output fuel pressure, very sad in my opinion, the rating of the fuel pump SHOULD in my opinion be what it is rated for, if there is some quality control on manufacturing, just my 2 cents, moving on.


Thanks guys, shes alive again.
 

32witha409

Well Known Member
Supporting Member 3
The spring in the mech pump is what determines the dead head fuel pressure. Must have had the wrong spring in it.
I regularly boost reference diaphragm pumps for turbocharging and that will raise pressures but only under boost.
 
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