engine stumbles when full throttle applied
Thread Starter
|
Senior User
Joined: Jul 2004
Posts: 123
Likes: 0
From: Thorold, Ontario, Canada
engine stumbles when full throttle applied
Hey everyone, I have a 460 that is basically stock and has a Holley 4 barrel carb, not sure if this is stock or not. Anyways she fires up and idles great, starts out at about 1000rpms, then when you tap the gas the idle drops to about 550rpms. MIght need to adjust the idle a bit but its not bad. Anyways when you give it a lot of gas it wants to die out, if you give it gas slowly its fine. Happens whether I am driving or just idling. At first we thought the timing may have been off, I checked it today and my timing is currently at 12 degrees.
Not sure how many miles are on this motor but its looking a little tired, the seals are all starting to leak, the motor is damp everywhere with oil. I just replaced the distributor cap and rotor, as well as the plugs. Any one have any idea why it woudl miss like this with sudden throttle?
Not sure how many miles are on this motor but its looking a little tired, the seals are all starting to leak, the motor is damp everywhere with oil. I just replaced the distributor cap and rotor, as well as the plugs. Any one have any idea why it woudl miss like this with sudden throttle?
Elder User
Joined: Jun 2004
Posts: 679
Likes: 0
From: Orlando, Fla
Your idle is a tad low, should be around 650-700. Sounds like your floats in your bowls need adjusting/sychronizing. Holleys are known for needing attention like that. How big of a Holley is it? I used a 650 on my 460 in a 79' Bronco and it screemed. I had to adjust my floats right out of the box. I believe you can go to Holley and download a schematic w/specs.
Posting Guru
Joined: Jun 2004
Posts: 1,635
Likes: 0
From: Niceville, FL.
Blown out power valve
Try replacing the power valve in the 4180 carburetor. Get the list number off the carburetor body and contact the Carburetor Support team at carburetor@holley.com and ask for the proper Holley power valve part number that is calibrated for your particular unit. Aftermarket power valves may not be set up for activation at the proper vacuum levels. The 4180 uses a two-stage power valve.
To get an idea about accelerator pump operation, remove the air cleaner and look down the front two barrels (engine off!) while rapidly operating the throttle linkage; you shoulg see gasoline being pumped into the carburetor throats.
Piffery1
To get an idea about accelerator pump operation, remove the air cleaner and look down the front two barrels (engine off!) while rapidly operating the throttle linkage; you shoulg see gasoline being pumped into the carburetor throats.
Piffery1
Moderator
Joined: Dec 2001
Posts: 22,436
Likes: 17
From: Louisville,Ky.
Does your vac. adv. have vacuum at an idle? If so, that can cause problems. Your timing will actually retard when you accelerate instaed of advancing.
With the engine off, look down the front barrels, open the throttle, gas should shoot out of the squirter down into the carb.
With the engine off, look down the front barrels, open the throttle, gas should shoot out of the squirter down into the carb.
Thread Starter
|
Senior User
Joined: Jul 2004
Posts: 123
Likes: 0
From: Thorold, Ontario, Canada
OK I did some searching, I should have a Holley 4160 600cfm 4 barrel carb, and from the pics I have found this looks right. A lot of the vacuum ports on the carb are plugged as the guy who had it before me removed a lot of excess stuff not needed, mostly smog stuff I believe so everything is plugged. I will do the checks you guys reccommend and see what happens.
On a side note, the adjustments screws on each side of hte carb, according tot he picture diagram they are called Idle limiter cap and idle adjustment screw, I thought these were the aitr anf fuel mixture adjustment screws? I adjust idle on the throttle stop screw, are the A/F mixture screws just called idle adjustment screws instead? When we turn them it effects the way the motor runs so I am assuming they are the mixture screws. On both sides at the front of the carb.
Sorry guys, I am not old enough to know carbs to well, I am used to EFI motors.
On a side note, the adjustments screws on each side of hte carb, according tot he picture diagram they are called Idle limiter cap and idle adjustment screw, I thought these were the aitr anf fuel mixture adjustment screws? I adjust idle on the throttle stop screw, are the A/F mixture screws just called idle adjustment screws instead? When we turn them it effects the way the motor runs so I am assuming they are the mixture screws. On both sides at the front of the carb.
Sorry guys, I am not old enough to know carbs to well, I am used to EFI motors.
Trending Topics
Posting Guru
Joined: Jul 2003
Posts: 2,232
Likes: 1
From: Colville, Washington
Those two screws are the idle mixture screws, they should be out about 1-1 1/2 turns from LIGHTLY seated. The vac advance can should be hooked to a port above the mixture screw on the pass. side of the carb. It will not have vacuum at idle. The list number( Holleys ID number) is on the front of the choke air horn. Do yourself a favor and get Holley replacement parts when you need them. JMHO
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
Moderator
Joined: Dec 2001
Posts: 22,436
Likes: 17
From: Louisville,Ky.
The two on the sides of the carb are the mixture screws. Sometimes they have plastic inserts that limit how far that you can turn them, but they can be pulled out.
Post the LIST number off of the front of the choke horn and I can give better details.
Post the LIST number off of the front of the choke horn and I can give better details.
Thread
Thread Starter
Forum
Replies
Last Post
black460
Big Block V8 - 385 Series (6.1/370, 7.0/429, 7.5/460)
16
Dec 6, 2004 05:50 PM
riggermortis
1987 - 1996 F150 & Larger F-Series Trucks
14
Sep 29, 2004 05:27 PM
