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Author Topic:   fuel pressure problems...getting $$expensive$$
posted July 29, 2004 09:42 AM
We are running a 383 in our Mod with a CSE bypass. I am pretty certain this is your typical bypass. Fuel supply coming from the Edlebrock mechanical pump, to the fuel log. First hose goes to the bypass, second and third hose goes to the carb, back of the fuel log goes to the pressure gauge. Bypass is mounted between the intake and carb. To control the bypass, there is a rod from the throttle linkage to the bypass box. Does this sound like a normal setup?

My main question is what we should set the fuel pressure to at idle (adjusting the rod length to the bypass), and what the pressure should be at full throttle?

Feel free to skip the following section. Iíll just be rambling trying to figure out why we are having engine problems:

We burned #3 and #5 pistons one week, and last time out we burned 2 valves (#2 and #3). The engine builder thinks the reason for this last problem was the spark plugs. We are running Champion J6ís and have been for a long time with no problems (slight possibility that we got the wrong plugs from the parts store Ė he said they almost look like glow plugs???). The electrode on #2 and #3 plugs were completely gone and I guess pieces got stuck between the valve and the seat. That last time out we turned 7600 in hot laps with no problems. When I went out for the heat race, the engine was cutting out from lap one. I probably stayed out one too many laps. We checked the fuel pressure at idle and it was at 10psi. Iíve heard it needs to be around 3-5. So we backed it down to 5 by adjusting the bypass rod, then reset the floats. A TON of adjustment was needed. Went out for the feature and only got 4 laps before burning the valves, temperature gauge pegged. Iím wondering if it started in the heat race. Did we lean out the motor because of the pressure being 10psi at idle? As I mentioned, we had the raise the floats a lot once we backed the pressure down to 5psi. Just a stab in the dark, I could be WAY off. Thanks for reading.

posted July 29, 2004 10:15 AM
Ditch the mechanical pump and use a good belt drive pump. The mechanical pumps just can't keep up with the flow you need. The fuel pressure should be about 3-5 psi at idle and 9-10 and the end of the straight. I've use both the system you use and the other ones that have the reguator on the end of the fuel log. both will work,in fact the current system I have has both the throttle bypass and the bypass at the end of the fuel log. One other thing run a good size fuel log mines about a 1 1/2" you should not have the problems, with the cheapy aluminum ones out you have no volume for the carb to draw from and your working on the bottom of the float bowls all the time .

posted July 29, 2004 02:16 PM
Dluna- I've experienced a similar problem with 2 of my engines lately. I kept fire slotting the block between #3/#5 and melting the edge of the piston. We too ran the same edelbrock pump. My fuel pressure was around 9psi off idle. Not sure what it really was under a load.

I've ran the same two engines numerous nights and never had any problems. The only difference with my car currently than in the past is now I'm a lot more hooked up than ever before, I'm running higher rpm's and the tires aren't spinning. I feel these type of conditions generate the need for more fuel to be delivered and the edelbrock mechanical pump just can't keep up.

I finally decided to change over to a KSE belt drive tandem fuel pump. All the old guys and engine builders that have been doing this forever will tell you the same thing.

I also changed to an MSD ignition and new carb. My car is also going on the dyno when we get the new engine put together so the jetting and timing can be analyzed. No more messing around.

Good luck to you.

posted July 29, 2004 02:17 PM
what did the plugs look like?

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