Hey all, wondering if there's anyone out there who can help me figure out what i need to do to get my fuel system working properly. I'll list some info below, if anyone has any pump curves for a DSR "0" pump that would be great, it's been really tough to get any good info on this since Darryl passed away.

Pump part number: DSR p/n 0-30069 (card says CCR rotation, 1.66 GPM @ 1800 RPM @ 50 PSI)
Engine: Iron block & Head SBC w/ Willy's 4412 carb. I have dyno sheets that show fuel usage in #/hr vs. rpms

Problem: Engine stumbles a lot on lower rpms, especially starts and restarts. It behaves like a rich stumble. I think the pump provides too much fuel to the carb for it to work properly so i'm looking for help on sizing a bypass system that will take the excess flow away from the carb to help it work more effectively. Waterman won't offer any technical help, only rebuild parts, as they don't have any performance data on the DSR pumps.

Any help or suggestions on who to talk to on getting this sized and sorted out would be greatly appreciated. Thanks!

What is the fuel pressure at the carb inlet under full load?

Does your fuel system have a Pill Holder that returns fuel to your fuel tank ?

@ Frank Reiner: I don't have a fuel pressure gauge installed. It's a Willy's Super Bowl carb, which I've heard multiple sources (incl. Willy's themselves) say that their arrangement can cause pressure spikes in the inlet line up to 100psi when suddenly dropping the throttle under full load. Obviously this complicates things.

@ Hustlin Hoosier: No it doesn't but I'm considering adding one to cut down on the flow going to the carb. I'm thinking it just doesn't need this much fuel but I'm struggling to figure out how to size that. Have heard from one friend that a Kinsler 3112 w/ a .100 pill is a good start, no idea where to start with quantifying that though.

1) Does the word "dropping" mean closing the throttle?
2) Can you provide pictures of the fuel system components: pump (as installed), pressure regulator, carb? Can you provide a sketch of the connections between components? What is the displacement of the engine? Gasoline or alcohol?
3) The fuel flow mentioned in your first post would support ~1200HP on gasoline!! Pro Stock territory.

1) yes, especially closing the throttle quickly. This makes it hard to put a pressure gauge on the system, so Willy's recommends that you don't use one at all. The only means you have of limiting your fuel pressure is limiting the restriction on your return line.
2) I've drawn a system schematic to the best of my abilities. The super bowl system is kind of weird, very little info available from it but the intent is to remove the needle & seat system, which i ran last year, varying pressure using a regulator between 3-9 psi. I still experienced similar issues before switching. It's a 355 ci small block chevy, right around 400 hp on the dyno
3) that's what was written on the tag when DSR sent the pump back to me in 2022. I haven't had the pump rebuilt but store it in Marvel Mystery Oil in the offseason and have no reason to believe it's got any issues. I swapped it out for a Waterman 400 for a few races last season and it ran nearly the same.

A very interesting system indeed. Typical floatless carburetors have a standpipe in the bowl to establish the fuel level, with the exit of the standpipe connected to a scavenge pump. The question here is: what in the valving of the Willy's system acts to create a low (below atmospheric) pressure condition at the scavenge connection?

For the immediate problem that you are facing: closing throttle at high rpm, a barrel valve that both closes to an idle flow rate to the bowl, and, diverts excess fuel to the return line (like a high-speed bypass in an injection system) would be required. The key to your problem would seem to be in the connections between supply and return. What guidance does Willy's offer?

Listening back to some GoPro footage from the other day, it's actually acting up on both deceleration and when I'm getting back onto the throttle (unless I didn't let the RPMs drop low enough, in which case it runs OK off the corner).

I'm running the -8 return line as suggested by Willy's. They are good to deal with for what they know (late models and mods) but don't seem to have too much of a response to the questions I was asking. The Super Bowl system doesn't even come with an info sheet on tuning or anything, they recommend having them install it and dyno test it, and it comes back to you with zero info. Calling them, I was able to get the pointers about upsizing the return line and hi flow vent, which i installed. I've now also heard from someone else with a similar issue that the return line needs to have as little vertical rise in it as possible, so I'm going to try rerouting that too.

Is your fuel pump camshaft driven or belt driven? If it is belt driven it could be run at a lower ratio (less than 1/2 speed), so as to reduce the overall flow rates.

The comments about vertical orientation of the return lines do tend to emphasize the desirability of a return scavenge pump. Would class rules permit that?

Could the combined return connections in the Willy's plumbing be separated into two returns, one for the overflow, and a separate one for the supply side to dump the pump output when the barrel valve is closed at high RPM?

To update all on how this ended up working out...

1. I determined that the engine was only ever going to use a maximum of 40% of the pump's output, so i went ahead and installed the Kinsler pill holder with a 0.104" pill. Immediately the car started idling better.
a) Note: It is important to install a shutoff valve for the bypass, otherwise the bowl won't get filled (Super Bowl has a 3psi check valve, and the Pill holder comes with a 2psi spring... pushing off at 750 rpm, the pump didn't create enough pressure to start filling the bowl. Had to install a valve, now i just open it after we push the car off and get it fired, works slick.

2. I tried messing around with different plugs. Initially was running NGK R5673-8 plugs, figured a hotter plug would help with combustion given that we run such low compression. Going to a -7 took all of my problems and made them worse. Going back to -8, everything ran a lot better. Counterintuitive, but the truth.

3. Plug gap made a big difference. With the above changes made, it was running about 80% better than before, but still stumbled if I got the rpms too low. Running a Vertex ext coil Mag by MagTech, I had the plugs gapped at 0.018" as per the recommendation of a local experienced Sprint engine builder, but after chatting with some other guys in the class it became apparent to me that most of em were running double the gap and getting better results. I went up to 0.036" and this immediately helped clean up the starts and firing.

Since we got the above figured out, I've been able to rattle off 4 wins in the last 6 weeks, so it's obviously running better. I figured I'd give you all an update as i appreciate the help in this forum and it's nice to get an update from the OP. Hopefully this can help someone else down the road!

Cheers,

Eric Guyot
#25 WRSS Sprint