High RPM + Long Duration = Crappy Performance

[Supertoys-Adventures]

When I'm on the gas hard for an extended period of time the truck bogs down or loads up or spark plugs stop sparking or I don't know what and then it dies. I thought it was a spark plug wire problem when it first happened or other issue but when I let it sit a while it drives as good as ever. I thought it was the carb but now I'm wondering if it's the spark. Why won't it stay running?:mad:

[CADTech]

sounds like a fuel pump problem or fuel filter problem.

[Sparky]

I agree that it sounds like fuel. Have you pulled the plugs to see what color they are when it dies? And how about some other info - make, model, engine, carb/efi, etc...

[scottm]

I agree its probably running out of fuel. Ideally you want to see the fuel pressure under load. About 5 psi at idle is normal, but you need at least 2 psi at the carb inlet at full throttle. Fuel press gauges are common on hi perf vehicles where running lean will quickly toast the engine, like blown offshore boats or nitroused drag cars. Putting a permanent gauge on it is not necessary of its obviously a clogged filter or worn out pump.

[Supertoys-Adventures]

88 Suburban with a 383 stroker GM Performance. Used to be TBI since changed to Carb Holley 870. I'm using the stock electric fuel pump with a regulator. Never checked the fuel pressure after running a while. Why does it pull hard if ran for a short time though? Filter has been replaced.

[scottm]

You have fuel stored in the bowls of the carb, and a pump that cant quite keep up. The stock tbi pump puts out more pressure than the carb needs, but the volume is only enough for about 200 hp.

[07FJRog]

You have fuel stored in the bowls of the carb, and a pump that cant quite keep up. The stock tbi pump puts out more pressure than the carb needs, but the volume is only enough for about 200 hp.

way more pressure,

get a diff pump and regulator, low pressure high volume pump

up to 7psi

[bigtex]

May be float levels set to low.What size fuel line do you run?? Sounds like a volume issue, do a flow test on your fuel pump.

[85yota]

I had same problem, switched out to -8 fuel lines and a bigger holley pump and it fixed it.

[offrdrob]

You have fuel stored in the bowls of the carb, and a pump that cant quite keep up. The stock tbi pump puts out more pressure than the carb needs, but the volume is only enough for about 200 hp.

Scott nailed it. The stock fuel pump is set up for an injected engine, High pressure-Low Volume.
You need to change to a fuel pump for a carb application. You would be fine with a 140 gal per hour pump, set up with a regulator at 6-7 psi.

[1audiohack]

The stock tbi pump puts out more pressure than the carb needs, but the volume is only enough for about 200 hp.

Yes to the first, no on the second part. I have run more than 500 crank HP on those pumps at low pressure, if they are not weak.

What have you got for a fuel pressure regulator? That pump is designed to run full flow against a bypass regulator sending what is not used by the engine back to the tank. An adjustable regulator set low for a carb is that fuel pumps dream. If you have it on a dead head regulator it will overheat and stop, and eventually fail.

It's also easy to accidentally circumvent (pun intended) the fueltank vent when "retrofitting" the fuel system. Try a test drive with the gas cap loose to eliminate the possibility that you are pulling a vacuum in the tank that the pump can't pull against. A small possibility with an in-tank pump but a very easy test.

All the best,
Barry.