390 Hesitates on takeoff

[Youngkidoldtruck]

i got a 390 in my 68 F-100 it starts up and everything but when i put my foot on the gas pedal, it hesitates alot like if it wants to stall before it accelerates, if i press the gas real slow it will slowly accelerate but if i try to accelerate fast, it will hesitate, i just rebuilt the carb so i have no idea whats wrong

[HIO Silver]

The hesitation is caused by needing a bit more fuel because it is leaning out at sudden acceleration. Assuming ya got a 2100, 2150, or 4100 carb, move the accelerator pump arm to the outboard hole...

[Youngkidoldtruck]

Im 15 so im kinda new to all this stuff, can i have like a schematic or a pic to show me what pump to move where plz

[HIO Silver]

I thought your generation is supposed to be versed in using Google.

See the rod at the right of the picture below? The rod connects to the arm on the accelerator pump cover. The arm has two holes... move the rod to the outboard hole on the arm.

[Dr Casti]

Im 15 so im kinda new to all this stuff, can i have like a schematic or a pic to show me what pump to move where plz

Well I'm 44 and I stil don't get this instructions....I have also the same problem when i step on the gas....maybe I'll replace the fuel pump....any other ideas in how to fix this....more clear please?

[Youngkidoldtruck]

I thought your generation is supposed to be versed in using Google.

See the rod at the right of the picture below? The rod connects to the arm on the accelerator pump cover. The arm has two holes... move the rod to the outboard hole on the arm.

[ Image ]

I have searched google and i cant find a way to move the pump arm, i have tried with pliers but it wont work and i think i may break it

[TNIceWolf]

You will need to remove the four screws holding on the accelerator pump housing....spring...and diaphragm as shown above. Of course while you are in there you should check the diaphragm itself for any wear...holes....cracking or other damage. You might find that it needs replaced as well. Also check the carb body and pump housing carefully for wear or erosion and when replacing the housing be very attentive to carefully retighten the screws in small increments one at a time in a criss cross fashion the prevent warping the plate for the pump.

[Youngkidoldtruck]

You will need to remove the four screws holding on the accelerator pump housing....spring...and diaphragm as shown above. Of course while you are in there you should check the diaphragm itself for any wear...holes....cracking or other damage. You might find that it needs replaced as well. Also check the carb body and pump housing carefully for wear or erosion and when replacing the housing be very attentive to carefully retighten the screws in small increments one at a time in a criss cross fashion the prevent warping the plate for the pump.

I dont think i really need to replace anything, i just rebuilt the carb since it was leaking, so everything else is good ill take your advice, hopefully my truck wont hesitate anymore

[colnago]

I had this problem in a Mazda pickup once. Tore the carb out, and took it to the local AutoZone for a rebuild kit. It ended up being a three dollar in-line fuel filter. The sudden need for gas caused sediment in the line to be picked up, and it clogged the filter. As soon as I let off the pedal, the vacuum went away, which let the sediment settle back down again, and the fuel could flow. It's a cheap, easy fix, and if it doesn't solve the problem, you're only out three bucks.

Joseph

[Dr Casti]

I had this problem in a Mazda pickup once. Tore the carb out, and took it to the local AutoZone for a rebuild kit. It ended up being a three dollar in-line fuel filter. The sudden need for gas caused sediment in the line to be picked up, and it clogged the filter. As soon as I let off the pedal, the vacuum went away, which let the sediment settle back down again, and the fuel could flow. It's a cheap, easy fix, and if it doesn't solve the problem, you're only out three bucks.

Joseph

That's a good thought!

[Youngkidoldtruck]

I had this problem in a Mazda pickup once. Tore the carb out, and took it to the local AutoZone for a rebuild kit. It ended up being a three dollar in-line fuel filter. The sudden need for gas caused sediment in the line to be picked up, and it clogged the filter. As soon as I let off the pedal, the vacuum went away, which let the sediment settle back down again, and the fuel could flow. It's a cheap, easy fix, and if it doesn't solve the problem, you're only out three bucks.

Joseph

actually, i just replaced the fuel filter,

[R.Smith]

I had a similar problem that turned out to be where my vaccum advance line was attached to the carb. I had it attached to the lower carb port. When a friend told me to put it on the upper carb port, the problem went away.

might also be a timing issue.