Force4

I dont have a 5.0 but this could be related to anything so I figure I will also post this here.
In 4th gear at about 4300-4500 RPM's my motor starts to randomly hesitate (feels quite jerky) but then it starts to smooth back out around 5000rpm. I am loosing my trap speed because of this and I dont know what would cause it. I am using a 750cfm 4 barrel carb. (summit street/strip) which is only a year old. My timing is not advance nor retarded(10 degrees). It only does it in 4th which is why I cant figure this out... first-third it just rips right to 6k. Any suggestions?

Force4

Update: Went to the track tonight, out of 3 runs the motor was hesitating in 3rd now also at around 4000-4500. Then I got on the freeway home and got on it a bit and it didnt start till 4th again. Sounds like a lack of fuel to me eh? Timing is exactly at 10 degrees so I do not think its the problem.

TrimDrip

lot a load in 4th, defiantly look at fuel

67mustang302

What do the plugs look like? Could be too lean, could be too rich. Does it get a surging hesitation? If it does then it's lean. If it has a blubbering type of hesitation, or seems to hiccup and stutter without surging or popping then it may be rich.

Has this problem suddenly started? If it's been fine but now this problem is occurring, then something has failed...fuel pressure problem, regulator, torn diaphragm etc.

Is the carb vacuum secondary? Post pics of the plugs.

Force4

Its running a vacuum secondary. Its consistency is leaning heavily towards a lack of fuel. Literally at like 5 grand in 3rd the motor just stops and starts to pop its way up slowly. If i get on it from a roll, the problem wont start until 4th. I am going to start basic and replace my fuel filter and put on a high volume fuel pump.

67mustang302

Check to see if the rubber diaphragm for the secondary activation is torn.

Force4

Good idea I'll check that also thanks