454 stumbles at 2500 rpm

[wjvineyard865]

Hey guys I’m new here from Tennessee. I’m need some help! I have a 84 k10 4wd with a 85 454 in it. I bought this truck a few months ago and the owner wasn’t the original builder so I don’t know much about the motor. But it starts great and runs great. Until the engine warms up and I hit 2500 rpms cruising. It will lose power and almost die. I can let out of the throttle and stay below 2500 rpm and it’ll run fine again. Here is what I’ve tried so far….replaced plugs, wires, fuel filer, dizzy, carb (Holley 850 Dp to 750 vac secondaries), played around with the timing. Right now it’s at 16* and 35* @2700, and also drove it with vac adv plugged to make sure it wasn’t too much vac.

 

[fast 99]

Check fuel pressure and volume

 

[wjvineyard865]

Think it’s sucking it dry?

 

[fast 99]

It's possible. Start with simple stuff.

 

[85K304SPD]

Clogged fuel line or sock in the tank. Maybe at the valve to change tanks . Open up the fuel line and see if you can blow air through it. Check it in sections until you find the clog. Make sure the system has a vent as well.

 

[wjvineyard865]

Ok thanks guys! I’ve got a fuel pressure gauge but that definitely doesn’t mean it’s reading right. But I haven’t messed with the lines yet because of that. I should know better then to assume something like that by now haha

 

[fast 99]

The truck can have pressure without flow, be sure and check that.

Had the same problem as your describing, new pumps and all sorts of unnecessary work/money later still had the issue. Turned out to be 2 defective pumps. Only found it by checking flow.

 

[Catbox]

Possible secondary tuning needed as well.

 

[wjvineyard865]

How did you check the flow?

 

[wjvineyard865]

And I haven’t messed with the secondaries on the new carb yet besides adjusting the float. I bought a quick change kit for the springs. I need to put it on tonight

 

[Bextreme04]

How did you check the flow?

unhook the fuel line from the carb and stick it in a container of some kind with a known volume. Crank the engine for a set number of seconds and see how much fuel came out

 

[82sbshortbed]

I know it's that dang ol holly. Get ya a good quadrajet, right @Paladin. Lol

 

[wjvineyard865]

Ok awesome I’ll give that a try!…and yeah both are hollys haha

 

[Matt69olds]

The cause is simple and obvious, it has a Holley on it. The solution?

Put a Q-Jet on it!!!

Your problem sounds like fuel delivery. Before spending too much time on it, remove the fuel cap. If that fixes the problem, the tank Indy venting. You can’t pull fuel out without letting some air in.

If that doesn’t solve it, start with the basics. Is the float level good? Fuel filter? Kinked fuel line?

If that’s all good, put a fuel pressure gauge on it. If you have fuel pressure when it’s acting up, you know it’s not a fuel starvation problem. It’s time to tear into the carb.

 

[wjvineyard865]

Well I had a buddy come over last night. Drove the truck around with gas cap cracked. Stil cut out at 2500 rpm while driving. Pulled mechanical fuel pump off and just quickly rigged up a holly blue electric pump with a regulator. Same problem…I’m at a loss here