Hesitation Problem
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Freshman User
Joined: Jul 2003
Posts: 28
Likes: 0
From: Akron,OH
Hesitation Problem
Hey guy's, I am having what I believe is some carburetion problems and wondered if you could help. Well, I just bought a 77 F100 and the previous owner put in a 351C 2V and it has a motorcraft 2 barrel carb on it. The truck starts fine, idle is a little high, and on take off it hesitates for a split second then picks up and takes off, then it is fine. and the only other time it does this is when you go to kick it into passing gear it hesitates the same way. I have changed plugs,wires,fuel filter,dizzy cap,rotor,points,air filter and still the same thing, I also noticed that whoever changed out the motors never re connected the "throttle selonoid" and i have no idea where to plug it in at? so i am assuming it is a carburetion problem. I am not much of a carb ace so any advice is greatly appreciated 
Thanks in advance,
Thanks in advance,
Posting Guru
Joined: Aug 2000
Posts: 1,127
Likes: 3
From: (near) Denver USA
Hesitation Problem
Throttle-opening hesitation is usually (95% of the time) caused by a lean out condition because air flow responds faster than fuel flow when you open the throttle.
It is most likely caused by an accelerator pump problem. You can try moving the accelerator pump rod to a hole farther away from the throttle shaft on the over-travel lever. Also, make sure the acc pump lever on the front of the carb is touching the diaphragm shaft when the throttle is closed (at idle). If not, re-bend the acc pump rod to adjust the lever position.
If those adjustments don't cure the problem, you may need to replace the acc pump diaphragm, the elastomer one-way valve, or the check valve ball. (All of those parts come in the carb rebuild kits.)
It is most likely caused by an accelerator pump problem. You can try moving the accelerator pump rod to a hole farther away from the throttle shaft on the over-travel lever. Also, make sure the acc pump lever on the front of the carb is touching the diaphragm shaft when the throttle is closed (at idle). If not, re-bend the acc pump rod to adjust the lever position.
If those adjustments don't cure the problem, you may need to replace the acc pump diaphragm, the elastomer one-way valve, or the check valve ball. (All of those parts come in the carb rebuild kits.)
Laughing Gas
Joined: Apr 2002
Posts: 846
Likes: 2
From: Bakersfield Ca.
Hesitation Problem
Originally posted by F100_77
I am not much of a carb ace so any advice is greatly appreciated
Thanks in advance,
I am not much of a carb ace so any advice is greatly appreciated
Thanks in advance,
With the engine off, pop the hood and remove the air cleaner. Climb up so you can look directly down into the carb. Now, grab the throttle linkage on the carb. and open it wide open quickly. If the accelerator pump is working you should see a healthy squirt of gasoline squirting down into the carb. from the nozzles in the top. If not, then that's you problem. Check to see if the accelerator pump is connected properly as suggested above by bubbaf250. If everything looks good, you'll have to replace the accelerator pump. Everything you'll need comes in a rebuild kit including instructions. Not a hard thing to do. Take your time and good luck. With everything you have done so far, this will be the last thing to do to complete your tune up. Keep us posted.
Thread Starter
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Freshman User
Joined: Jul 2003
Posts: 28
Likes: 0
From: Akron,OH
Hesitation Problem
Well, I checked the accelerator pump and it is working fine supplies the gas to the carb just fine. the accelerator pump rod is allready in the hole farthest away from the throttle shaft on the over-travel lever, and the accelerator pump lever is resting against the diaphram shaft while the throttle is closed ( at idle ) So you guys think its time for a trip to the parts store for a re build kit 
Senior User
Joined: Jun 2003
Posts: 439
Likes: 0
From: Burnsville, MN
Hesitation Problem
Throttle solenoid is the anti-runon (dieseling) solenoid that was common for smogger engines. This should be connected to a 12 volt source that is hot while the key is in the run position. Failure to make this connection, sets the carb in an overly lean condition due to the postion of the butterfly. You usually have a very slow idle that is a bit rough. This may explain some of your issues.
Since you say the accelerator pump is OK, I would then suspect that the float level in the carb is too low, this will increase the amount of time that it takes for the carb main system to supply fuel through the venturi.
Since it sounds like you have the wrong carb installed (throttle solenoid issue) and a potential carb issue - I'd suggest that you obtain the correct carb for the motor. If you want to save a few $ you can play around with some of the items suggested here.
Good luck to you!
Since you say the accelerator pump is OK, I would then suspect that the float level in the carb is too low, this will increase the amount of time that it takes for the carb main system to supply fuel through the venturi.
Since it sounds like you have the wrong carb installed (throttle solenoid issue) and a potential carb issue - I'd suggest that you obtain the correct carb for the motor. If you want to save a few $ you can play around with some of the items suggested here.
Good luck to you!
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