454 stumbles at 2500 rpm

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

wjvineyard865

Junior Member
Joined
Sep 8, 2022
Posts
13
Reaction score
0
Location
knoxville, Tn
First Name
Wesley
Truck Year
1984
Truck Model
k10
Engine Size
454
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

Full Access Member
Joined
Dec 31, 2021
Posts
1,589
Reaction score
2,150
Location
Spokane, Washington
First Name
Brian
Truck Year
81,85
Truck Model
K20
Engine Size
350
It's possible. Start with simple stuff.
 

85K304SPD

Full Access Member
Joined
Mar 29, 2022
Posts
386
Reaction score
571
Location
Las Cruces, NM
First Name
Richard
Truck Year
1985
Truck Model
K30
Engine Size
383
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

Junior Member
Joined
Sep 8, 2022
Posts
13
Reaction score
0
Location
knoxville, Tn
First Name
Wesley
Truck Year
1984
Truck Model
k10
Engine Size
454
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

Full Access Member
Joined
Dec 31, 2021
Posts
1,589
Reaction score
2,150
Location
Spokane, Washington
First Name
Brian
Truck Year
81,85
Truck Model
K20
Engine Size
350
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.
 

wjvineyard865

Junior Member
Joined
Sep 8, 2022
Posts
13
Reaction score
0
Location
knoxville, Tn
First Name
Wesley
Truck Year
1984
Truck Model
k10
Engine Size
454
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
 

wjvineyard865

Junior Member
Joined
Sep 8, 2022
Posts
13
Reaction score
0
Location
knoxville, Tn
First Name
Wesley
Truck Year
1984
Truck Model
k10
Engine Size
454
Ok awesome I’ll give that a try!…and yeah both are hollys haha
 

Matt69olds

Full Access Member
Joined
Jan 8, 2018
Posts
2,338
Reaction score
3,571
Location
Central Indiana
First Name
Matt
Truck Year
81
Truck Model
GMC 1/2 ton
Engine Size
455 Olds
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

Junior Member
Joined
Sep 8, 2022
Posts
13
Reaction score
0
Location
knoxville, Tn
First Name
Wesley
Truck Year
1984
Truck Model
k10
Engine Size
454
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
 

Forum statistics

Threads
41,859
Posts
903,686
Members
33,372
Latest member
83elcowes
Top