Engine hesitation
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
Likes: 420
From: Long Island USA
You need more of an accelerator pump shot probably (or might have TOO much).
When you do this, does it spit black smoke out the tailpipe(s) ?
If not, whatever the Avenger used to adjust the accelerator pump needs to be increased. On the standard vac-sec 750 I have (had) that was done with a pump cam that screws onto the throttle plate lever.
Also, based on what you say, you may need a bigger "shooter" - the actual holes that spray gas into the barrels. This will increase the initial shot of gas into the engine even if you dont' change the pump cam. Check out what to tune on your specific carb.
When you do this, does it spit black smoke out the tailpipe(s) ?
If not, whatever the Avenger used to adjust the accelerator pump needs to be increased. On the standard vac-sec 750 I have (had) that was done with a pump cam that screws onto the throttle plate lever.
Also, based on what you say, you may need a bigger "shooter" - the actual holes that spray gas into the barrels. This will increase the initial shot of gas into the engine even if you dont' change the pump cam. Check out what to tune on your specific carb.
Elder User
Joined: Jan 2004
Posts: 867
Likes: 0
From: Eastern Pa
I agree with Krewat. You need to define your hesitation. Is it just when you nail it from a cruise? Does it kinda sputter and then pick up? Or is it just a brief lag and then go? If it's the latter it's in the accelerator pump somewhere. The cam will change when and for how long the shot comes. But if that doesn't cure it you need the larger squirters.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
First check the accellerator pump adjustment. If It isn't squirting as soon as you move the throttle the motor will stumble off idle every time. Rarely will idle mixture cause a stumble and usually timing won't either unless it is retarded too much and that doesn't sound like your setup.
Thread Starter
|
Senior User
Joined: Sep 2003
Posts: 131
Likes: 1
engine hesitation
Now that i have got the exhaust hooked up and drove it a bit more, i can say i have more of a miss rather than a hesitation. It idles neer perfect, however if i crack it just a tad, less than 1/4 throttle, it has a definate steady miss. at more than 1/4 throttle, it clears up and runs like a champ. So it is near impossible to cruise because the motor just misses. What you think?
Trending Topics
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Ford Super Duty: 5 Things Owners LOVE, 5 Things They LOATHE!
Joe Kucinski
Every 2026 Ford Truck Engine RANKED from WORST to FIRST!
Michael S. Palmer
The Best F-150 Deal of Every Trim Level (XL through Raptor)
Joe Kucinski
FE "Freakin Expensive"
Joined: Dec 2003
Posts: 6,461
Likes: 4
From: Smith Mountain Lake, VA
Yep First off...Check the clearence on the pump..it should be touching..no slack at all...and yet not putting any pressure on the pump arm....And I dont know..If those carbs come with the anti backfire blowout prtection for the Power Valve or not??
But if they didnt?? and it has sneezed thru the carb (backfire) you may have blown out the power Valve....which is located on the Primary metering block...
Good Luck!!
Russ
But if they didnt?? and it has sneezed thru the carb (backfire) you may have blown out the power Valve....which is located on the Primary metering block...
Good Luck!!
Russ
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Originally Posted by tastyklair
The idle mixture screws will have no effect once you crack the throttle. The intermidiate circuit is in control by 1000 rpm.
Elder User
Joined: Jan 2004
Posts: 867
Likes: 0
From: Eastern Pa
Actually the idle mixture screws contol the mixture below the throttle plates when they are closed and there is high manifold vacuum. As soon as the butterfly opens just a couple of degrees the idle transfer holes are exposed allowing more fuel in because the ones below the butterfly now don't have enough vacuum to get enough fuel in by themselves. The further the butterfly is opened the greater the drop in vacuum and the idle circuit and off idle circuit are nearly dead. Velocity now takes over in the venturi and creates high velocity at the center of the venturi that creates a low enough atmospheric pressure that gas is pushed through the main metering sytem into the low pressure zone. In between these two functions there is a gap that needs to be filled and thats where the accelerator pump comes in.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Originally Posted by tastyklair
Actually the idle mixture screws contol the mixture below the throttle plates when they are closed and there is high manifold vacuum. As soon as the butterfly opens just a couple of degrees the idle transfer holes are exposed allowing more fuel in because the ones below the butterfly now don't have enough vacuum to get enough fuel in by themselves. The further the butterfly is opened the greater the drop in vacuum and the idle circuit and off idle circuit are nearly dead. Velocity now takes over in the venturi and creates high velocity at the center of the venturi that creates a low enough atmospheric pressure that gas is pushed through the main metering sytem into the low pressure zone. In between these two functions there is a gap that needs to be filled and thats where the accelerator pump comes in.
New User
Joined: Mar 2004
Posts: 18
Likes: 0
From: Knoxville, TN
Adjust the mixture screws
I had the exact same problem with my carb. All I did was richen up the idle mixture screws. Turn them counter clockwise half a turn at a time and test drive it until it smooths things out.