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Mastertech1, ASE Master Technician
Category: Car
Satisfied Customers: 2261
Experience:  30 years of all phases automotive diagnostics and repair
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The 345 V8 runs great at idle..and when running..60 mph..accelerator

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My 1974 IHC Scout II with the 345 V8 runs great at idle..and when running up to around 60 mph. If you give full throttle at the 55-60 mph mark, or higher, the engine chokes down as if the accelerator is being continually pushed and released. Also, the engins backfires and sputters. If you put the truck in neutral and rev the engine, it continues to do the same thing. If you let off of the accelerator, and slow to a slower speed and then hold the accelerator steady, it will run normal....and then you can accelerate again.

I just replaced the cap, button, wires, and plugs.... The Scout has a Carter AFB carb, and has had electronic ignition installed....What could my problem be?

I WOULD LIKE TO THANK YOU FOR CHOOSING JUST ANSWER, AND FOR ALLOWING ME THE OPPORTUNITY TO ASSIST YOU WITH YOUR AUTOMOTIVE CONCERNS.This sounds to be fuel related, Have you tested fuel pressure, or replaced the fuel filter? Thanks, XXXXX XXXXX know
Customer: replied 6 years ago.

I have not replaced the fuel filter recently, but I did take it loose and look at it. It appeared to be clean. I installed new fuel lines and tank about 3 years ago. The tank isn't a pressurized tank, as it appears to self vent. When I replaced the tank, I also replaced the sending unit.


Does it appear to be too much fuel or too little fuel. The backfiring and choking out confuses me..



When I am talking about fuel pressure,I mean fuel pump output pressure (the fuel delivery from tank to carburator) The issue sounds to be low fuel pressure,or the float level in the carburator , is not allowing the proper amount of fuel in the carb. float bowl, In turn the engine will run like you have decribed it, Thanks, XXXXX XXXXX know!
Customer: replied 6 years ago.
Sounds like I could use a carb rebuild, anyway. How can I check the fuel pressure from the pump?
Remove the fuel supply line from the carb, and connect it to a fuel pressure tester (you can use the old school type tester for this(,most parts houses sell them for $15.00) With the tester connected, crank over the engine and see what the pressure reads, It should be 3 psi to 6psi If it tests good, Then open top of carb. and set float to proper setting (all carb. kits come with the measuring devise and specs. for setting) Thanks, XXXXX XXXXX know if I can be of any other assistance to you with this issue!
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